WO2019233876A1

WO2019233876A1 - Light concentrator module

Info

Publication number: WO2019233876A1
Application number: PCT/EP2019/064078
Authority: WO
Inventors: Simon Eme Kadijk; Ludovicus Johannes Lambertus HAENEN; Diego VERMEULEN; Cornelis Johannes Maria DENISSEN; Vinicius BRAUN DE BORTOLI; Riff Jf SHI; Johannes Martinus Jansen; Roelof Koole
Original assignee: Signify Holding B.V.
Priority date: 2018-06-05
Filing date: 2019-05-29
Publication date: 2019-12-12

Abstract

The invention provides an arrangement (500) of an elongated light transmissive body (100) and a beam shaping optical element (224), wherein: - the elongated light transmissive body (100) has a side face (140) and a radiation exit window (112), wherein the elongated light transmissive body (100) comprises a luminescent material (120) configured to convert at least part of light source light (11) into luminescent material light (8); - the beam shaping optical element (224) comprises a beam shaping light transmissive body (210) having a radiation entrance window (211) optically coupled with the first radiation exit window (112) and part of the side face (140) for receipt of at least part of the luminescent material light (8).

Description

Light concentrator module

FIELD OF THE INVENTION

The invention relates to a light generating device comprising a light source and an arrangement of an elongated light transmissive body and a beam shaping optical element. Further, the invention relates to such light generation device for use in a projector, or for use in stage lighting, or for use in a luminaire. The invention also relates to a method of producing such arrangement.

BACKGROUND OF THE INVENTION

Luminescent rods are known in the art. W02006/054203, for instance, describes a light emitting device comprising at least one LED which emits light in the wavelength range of >220 nm to <550 nm and at least one conversion structure placed towards the at least one LED without optical contact, which converts at least partly the light from the at least one LED to light in the wavelength range of >300 nm to <1000 nm, characterized in that the at least one conversion structure has a refractive index n of >1.5 and <3 and the ratio A:E is >2:1 and <50000:1, where A and E are defined as follows: the at least one conversion structure comprises at least one entrance surface, where light emitted by the at least one LED can enter the conversion structure and at least one exit surface, where light can exit the at least one conversion structure, each of the at least one entrance surfaces having an entrance surface area, the entrance surface area(s) being numbered Ai ... A_n and each of the at least one exit surface(s) having an exit surface area, the exit surface area(s) being numbered Ei ... E_n and the sum of each of the at least one entrance surface(s) area(s) A being A = Ai +A₂ ... + A_n and the sum of each of the at least one exit surface(s) area(s) E being E = Ei +E₂ ... +E_n.

W02003/009012A2 discloses a light source with a light collector comprising a sheet of material having a fluorescent substance incorporated therein and an optical element juxtaposed adjacent the collector. Light incident on the collector induces fluorescence that is trapped by total internal reflection, concentrated, and radiated from an edge of the collector. The size of collector plate with respect to its thickness is such that it provides an intensified image along its edge that is readily visible during both daytime and nighttime. The optical element modifies the distribution of light output from an edge of the collector. The optical element is preferably configured to decrease divergence of light emitted from the edge. The optical element may also direct the light emitted from the collector above or below the plane of the collector.

SUMMARY OF THE INVENTION

High brightness light sources are interesting for various applications including spots, stage-lighting, headlamps and digital light projection, etc.. For this purpose, it is possible to make use of so-called light concentrators where shorter wavelength light is converted to longer wavelengths in a highly transparent luminescent material. A rod of such a transparent luminescent material can be illuminated by LEDs to produce longer wavelengths within the rod. Converted light which will stay in the luminescent material, such as a

(trivalent cerium) doped garnet, in the waveguide mode and can then be extracted from one of the (smaller) surfaces leading to an intensity gain.

In embodiments, the light concentrator may comprise a rectangular bar (rod) of a phosphor doped, high refractive index garnet, capable to convert blue light into green light and to collect this green light in a small etendue output beam. The rectangular bar may have six surfaces, four large surfaces over the length of the bar forming the four side walls, and two smaller surfaces at the end of the bar, with one of these smaller surfaces forming the “nose” where the desired light is extracted.

Under e.g. blue light radiation, the blue light excites the phosphor, after the phosphor start to emit (green) light in all directions (assuming some cerium comprising garnet applications). Since the phosphor is embedded in - in general - a high refractive index bar, a main part of the converted (green) light is trapped into the high refractive index bar and wave guided to the nose of the bar where the (green) light may leave the bar. The amount of (green) light generated is proportional to the amount of blue light pumped into the bar. The longer the bar, the more blue LED’s can be applied to pump phosphor material in the bar and the number of blue LED’s to increase the brightness of the (green) light leaving at the nose of the bar can be used. The phosphor converted light, however, can be split into two parts.

A first part consists of first types of light rays that will hit the side walls of the bar under angles larger than the critical angle of reflection. These first light rays are trapped in the high refractive index bar and will traverse to the nose of the bar where it may leave as desired light of the system. A second part consists of second light rays (“second light rays”) that will hit the side walls of the bar at angles smaller than the total angle of reflection. These second light rays are not trapped in the bar but will leave the bar at its side walls. These second light rays may be bounced back into the (garnet) bar, but in such cases these light rays will always enter the (garnet) bar under angles smaller than the total angle of reflection, will traverse straight through the (garnet) bar and leave the bar at the opposite side wall. Such, these second light rays will never channel to the nose of the bar. These second light rays are lost and will limit the efficiency of such illumination systems. Typically, in current systems, 44% of the converted light is trapped and will leave the (garnet) bar at its nose, while 56% of the converted light is lost at the side walls of the bar.

It appears that an arrangement of an elongated luminescent body with a collimator at an end face, and with especially illumination at a side face, may have light losses when the collimator has a different index of refraction than the material of the luminescent body, especially when the index of refraction is lower. Further, it appears that an arrangement of an elongated luminescent body with a collimator at an end face, and with especially illumination at a side face, may have an increase in etendue when the collimator has a substantially same index of refraction as the material of the luminescent body, compared to an arrangement wherein the indices of refraction are different.

It appears therefore desirable to provide an alternative arrangement wherein the light loss is decreased and/or wherein the etendue (change) is at desirable values. Hence, amongst others, it is an aspect of the invention to provide an alternative arrangement of luminescent body and beam shaping element and/or light generating device, which preferably further at least partly obviate(s) one or more of above-described drawbacks and/or which may have a relatively higher efficiency. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

In a first aspect, the invention provides a light generating device comprising a light source configured to generate light source light and an arrangement of an elongated light transmissive body (“body” or“elongated body” or“luminescent body”) and a beam shaping optical element (“beam shaping element” or“optical element”), wherein the elongated light transmissive body having a first face and a second face defining a length of the light transmissive body, a side face and a first radiation exit window, wherein the second face comprises the first radiation exit window, and wherein the elongated light transmissive body comprises a luminescent material configured to convert at least part of light source light into luminescent material light, and wherein the beam shaping optical element comprises a beam shaping light transmissive body (“beam shaping body”) having a radiation entrance window optically coupled with the first radiation exit window (“light exit window”) and part of the side face along the full circumference of the second face and for less than 5 % of the total area of the side face, for receipt of at least part of the luminescent material light. The beam shaping optical element is a compound parabolic concentrator.

Herein, the arrangement is especially further elucidated with reference to the use of a light source that generates the light source light. The combination of arrangement and light source is also part of the invention. A light generating device is provided comprising a light source configured to generate the light source light and the arrangement as defined herein.

It appears that with such arrangement, the light that is outcoupled from the beam shaping element within the desired etendue can be increased relative to an arrangement wherein the beam shaping element is only in optical contact with the light exit window. Further, it appears that additional modifications, such as using a non-planar radiation exit window may further increase the light outcoupling. The invention, while optionally also using a non-planar radiation exit window, may also facilitate alignment of the elongated body and the beam shaping element. The present invention also allows a more robust arrangement.

In the arrangement, the elongated light transmissive body is configured to receive light source light and convert that into luminescent material light (“luminescent light”). Especially, when a plurality of light sources is applied (see also below), (luminescent material) light may be concentrated and a strong light beam may be generated. The elongated light transmissive body especially has light guiding properties for the luminescent material light (and also for the light source light). Light source light may be coupled into the elongated light transmissive body via a side face and/or via an end face, especially via (at least) a side face (see further also below). Light source light may also be coupled into the elongated light transmissive body via a plurality of side faces.

Hence, especially the elongated light transmissive body has a side face and a radiation exit window, wherein the elongated light transmissive body comprises a

luminescent material configured to convert at least part of light source light into luminescent material light. As will be further elucidated below, light source light, especially from a plurality of light sources, may enter the elongated light transmissive body via a side face of the elongated light transmissive body, is (at least partly) converted into luminescent material light, and at least part thereof escapes from the elongated light transmissive body via a radiation exit window (of the elongated light transmissive body). The radiation exit window is especially comprised by an end face. In embodiments, the end face of the elongated light transmissive body is the radiation exit window.

Light that escapes from such radiation exit window is especially beam shaped with a beam shaping element. The beam shaping element is configured downstream of the radiation exit window. The beam shaping element may especially have a collimation function. For instance, the beam shaping element may be a compound parabolic concentrator (CPC) or similar kind of concentrator (see also below).

Especially, the beam shaping element comprises a massive light transmissive body, and optionally further optical elements, like a reflector surrounding part of the light transmissive body. Surprisingly, it appears that when the shape of the light transmissive body is choses such that a small part, sometimes even a tiny part, extends beyond the radiation exit window over the side face, light outcoupling can be enhanced, while etendue may be maintained.

Therefore, especially the beam shaping optical element comprises a beam shaping light transmissive body having a radiation entrance window optically coupled with the first radiation exit window and part of the side face for receipt of at least part of the luminescent material light. As indicated above, especially the beam shaping optical element is configured to beam shape the received luminescent material light. As the term“side face” may also refer to a plurality of side faces (such as four side faces in embodiments wherein the elongated light transmissive body has a rectangular cross-section), the beam shaping optical element may in embodiments also be optically coupled with one or more parts of one or more (of the plurality of) side faces, respectively.

The elongated light transmissive body may especially be based on a cerium comprising garnet material (see also below), which has a relatively high index of refraction. The beam shaping element may - in embodiments - be based on the same type of material, with no or a very low cerium concentration. However, using such type of material, especially for the purposes of the invention, appears challenging. For instance, the etendue may increase and the use of an optically useful suitable adhesive material appears very difficult. Hence, it appears to be useful to use a material for the beam shaping element transmissive body that is different from the material of the elongated light transmissive body. In general, the beam shaping light transmissive body has an index of refraction that is lower than of the elongated light transmissive body, which may be useful in view of minimizing the etendue, though less useful in view of outcoupling efficiency. Therefore, in embodiments the elongated light transmissive body has a first index of refraction ( ), and the beam shaping light transmissive body has a second index of refraction (n₂) which is smaller than the first index of refraction. For instance, the difference in index of refraction may be larger than 0.1 (at 500 nm light), such as even larger than 0.2. For instance, the index of refraction of YAG (see also below), is about 1.86 at 500 nm, of polycarbonate about 1.61 (at 500 nm), and of silicone about 1.4 (at 500 nm). Herein, indices of refraction especially refer to those indices when using light of 500 nm.

Suitable materials for the elongated body are described below. Such materials may also be used for the beam shaping light transmissive body (i.e. for the beam shaping light transmissive body material). The material of the beam shaping light transmissive body is thus not necessarily the same as of the elongated body. Especially, its index of refraction (n₂) may especially be lower than of the elongated light transmissive body (material) ( ).

The length of the elongated body may essentially be any length. When the light sources are small, like micro type LEDs, the elongated body may be short, if desired. The longer the elongated body, the more light source light can be coupled into a side face. In general, the length of the elongated body will be at least about 2 cm (see also below). As already indicated above, the length over which the beam shaping light transmissive body may have optical contact with the side face may be very small, such as lower than 10 mm, in general lower than 5 mm. Therefore, in embodiments the length over which the beam shaping light transmissive body may have optical contact with the side face may be in the range of 0.05-5 mm, such as at least about 0.1 mm, like selected from the range of 0.1-5 mm, like especially selected from the range of 0.1-0.5 mm.

In specific embodiments, assuming an elongated body having a rectangular cross-section with height h and length w, and a first refractive index nl, the length over which the beam shaping light transmissive body having a second refractive index, may have optical contact with the side face may be about a*sqrt(h²+ w²)/tan(asin(ni/n₂)), wherein a is a factor indicating a marge and is selected from the range of 0.9- 1.1 , such as 1.0.

Optical contact may especially imply that the average distance between the indicated elements is equal to or smaller than 1 pm, such as equal to or smaller than 0.5 pm, like equal to or smaller than 0.4 pm. Alternatively, or additionally, there may be an intermediate light guiding material configured between elements, such as a light transmissive adhesive. For instance, silicone glue may be used to provide optical contact. In general, the layer thickness of the intermediate light guiding material between the two elements is limited, such as in average in the range of 5-5000 pm, like in the range of 5-1000 pm, such as especially 5-500 pm, like especially 20-100 pm. In other embodiments, however, the elements may be in physical contact with each other.

One way to control the extend of overlap of the beam shaping light transmissive body with the elongated body may be to provide the beam shaping light transmissive body with an indentation. This may also facilitate alignment of the beam shaping light transmissive body and the elongated body. Therefore, in embodiments the radiation entrance window comprises an indentation hosting part of the elongated light transmissive body. In specific embodiments, the indentation has a depth selected from the range of 0.05-10 mm, such as especially from the range of 0.1-5 mm.

It further appears to be beneficial in terms of outcoupling from the elongated body (into the beam shaping element) that the first radiation exit window is non-planar. In embodiments the first radiation exit window is one dimensionally curved. In yet other embodiments, the first radiation exit window is two dimensionally curved. In yet other embodiments, the first radiation exit window is facetted. Combinations may also be possible, such as curved facets, or facets that are joined by curved edges.

In embodiments, the first radiation exit window comprises facets thereby creating different facet angles relative to a plane of the first radiation exit window. In embodiments, the plane has at least two facets, e.g. a wedge-shaped window. Even more especially, the plane has at least four facets, such as a tetragonal pyramid shaped window. However, with e.g. four facets, also a kind of checker board structure or saddle shape structure can be provided, with two faces forming a top and two faces forming a cavity. However, many more shapes are possible, including multi-faceted shapes and curved shapes (see also above). In specific embodiments, the plane comprises n/cm² facets, wherein n is selected from the range of 1-10,000, such as 1-1000. The plane may be configured essentially perpendicular to a body axis of the elongated body.

Using a non-planar first radiation exit window may be done in combination with a radiation entrance window of the beam shaping element that is planar. However, such radiation entrance window may also include an indentation, as indicated above. In specific embodiments, the radiation entrance window may include a structure (or shape) that is complementary to the non-planar radiation exit window. Thereby, a male-female coupling may be facilitated.

Hence, in embodiments the first radiation exit window is non-planar, and the indentation (in the beam shaping element) may have a shape corresponding to the non-planar first radiation exit window (thereby allowing a male-female configuration). As indicated above, optical contact may in embodiments be via physical contact. Therefore, in embodiments the beam shaping light transmissive body may be in physical contact with one or more of the first radiation exit window and part of the side face. The beam shaping light transmissive body may be in physical contact with both the first radiation exit window and part of the side face. In specific embodiments, the beam shaping light transmissive body may be in physical contact with only one of (i) the first radiation exit window and (ii) part of the side face, especially with only the first radiation exit window.

As indicated above, the beam shaping element comprises beam shaping light transmissive body material, which may be selected from the same light transmissive materials as herein defined in relation to the elongated body.

In embodiments, the beam shaping light transmissive body is a monolithic body comprising a beam shaping light transmissive body material is selected from the group of quarts, glass, ceramic and polymer. When the beam shaping light transmissive body is of polymeric material, the beam shaping light transmissive body may be overmolded on(to) the elongated body. In specific embodiments, PMMA or PC (or a combination thereof), or COC, may be applied as beam shaping light transmissive body material.

Hence, embodiments the beam shaping light transmissive body is an overmolded body. Especially, in embodiments the beam shaping light transmissive body material comprises a polymer material. Yet further, in embodiments the polymer material comprises silicone. Silicone material may be relatively transmissive for visible light.

As indicated above, optical contact may be achieved by physical contact between the elements that are (thereby) in optical contact. Alternatively or additionally, there may be a light guiding material be configured between the elements. In this way, also optical contact may be achieved. The light guiding material may be a material as defined below, especially in relation to the elongated body. Especially, however, here the intermediate material, intermediate between the two elements that are optically coupled, may be used as (kind of) adhesive. Hence, the intermediate material may e.g. be frit material, such as in case that both elements are selected from the group consisting of quartz, glass, and ceramic, or may be adhesive material, such as a silicone adhesive. Therefore, in embodiments between one or more of (i) the beam shaping light transmissive body and the first radiation exit window, and (ii) the beam shaping light transmissive body and the part of the side face, a light transmissive material is configured, wherein the light transmissive material is selected from an adhesive material and a frit material. In specific embodiments, as (kind of) adhesive material, in embodiments also a thermoplastic polymer can be applied, such as e.g. PMMA or PC, or COC. For instance, the elements may be joint-melted. Hence, by welding a polymeric material, the elements may be connected.

When the beam shaping light transmissive body is a monolithic body, e.g. an adhesive material (or frit material) may be used to provide a connection between the two elements, which connection provides the optical coupling. In such embodiments, the material of the beam shaping light transmissive body may provide the kind of sleeve which allows the optical coupling with part of the side face.

In yet other embodiments, the part of the beam shaping light transmissive body that provides the optical coupling with the side face may be another material than the remainder of the beam shaping light transmissive body. For instance, this may be the case when a truncated beam shaping element, such as a truncated collimator (like a truncated CPC), is applied. In such embodiments, the radiation entrance window may be larger than the first radiation exit window. The shape of the truncated beam shaping light transmissive body may be supplemented by material that is light transmissive, such as light transmissive polymeric material, like the herein described adhesive material or frit material.

Therefore, in embodiments the beam shaping light transmissive body is a composite body, comprising a first part that is in physical contact with the part of the side face, and a second part that is in optical contact with the first radiation exit window. In specific embodiments, the first part is selected from an adhesive material, such as a silicone glue, and a frit material, such as a frit glass. Polymeric material other than adhesive material may also be applied to provide the optical coupling with the side face.

The second part, or main part, may e.g. essentially consist of PMMA or PC (or a combination thereof), or COC.

The first part may in embodiments be silicone. Further, in embodiments the monolithic beam shaping light transmissive body may be silicone. Therefore, in

embodiments the beam shaping light transmissive body material comprises silicone. Suitable silicones may e.g. be Dow Coming MS-1002, MS-1003 or silopren momentive LSR7060, LSR7070FC, or LSR7080J. Another suitable silicone may be Wacker Elastosil LR7600.

In embodiments, the first part comprises equal to or less than about 10 vol.% of the total volume of beam shaping light transmissive body, and the second part comprises equal to or more than 90 vol.% of the total volume of the beam shaping light transmissive body. The beam shaping light transmissive body is especially a solid body. Especially, the silicones that are herein described are optical grade silicones that can e.g. also be used for optical lenses (on e.g. LEDs). Further, in specific embodiments herein silicones are applied that have an index of refraction of at least 1.45, such as at least 1.5.

As indicated above, the beam shaping optical element is configured to shape a beam of light of the luminescent material light that escapes from the radiation exit window and enters the beam shaping optical element via its radiation entrance window. The type of beam shaping may depend upon the desired use. Hence, in embodiments the beam shaping optical element is selected from the group consisting of a compound parabolic concentrator (CPC), an adapted compound parabolic concentrator, a dome, a wedge-shaped structure, and a conical structure.

As indicated below, the term“light source” may also refer to plurality of (different) light sources.

Such light generating device may be used as or may be comprised by a luminaire. Such light generating device may also be applied in a projection system.

Therefore, in yet a further aspect the invention also provides a projection system or a luminaire comprising the light generating device as defined herein. The light generating device may especially be configured to provide light generating device light. This light may comprise the luminescent material light.

In yet a further aspect, the invention also provides a method for producing such arrangement. This may be done in several ways, such as gluing together, overmolding, arranging in physical contact, etc. etc. Especially, the arrangement may be provided as single (composite) element consisting of the elongated light transmissive body and the beam shaping optical element. Therefore, the invention further provides a method comprising providing the elongated light transmissive body and providing the beam shaping optical element by one of (i) overmolding the beam shaping optical element to the elongated light transmissive body and (ii) connecting the beam shaping optical element and the elongated light transmissive body with an adhesive material or a frit material, such that the radiation entrance window is optically coupled with the first radiation exit window and part of the side face. Alternatively (or additionally), a support structure may be provided, wherein the elongated light transmissive body and the beam shaping optical element are hold, whereby the arrangement is provided (and optical contact is guaranteed).

Below, some further embodiments are elucidated. In embodiments, the arrangement of light generating device comprises a luminescent element. The luminescent element comprises an elongated light transmissive body having a first face and a second face defining a length (L) of the light transmissive body, the light transmissive body comprising one or more radiation input faces and a first radiation exit window, wherein the second face comprises the first radiation exit window; the elongated light transmissive body comprising a luminescent material configured to convert at least part of light source light received at one or more radiation input faces into luminescent material light, and the luminescent element configured to couple at least part of the luminescent material light out at the first radiation exit window as converter light.

The first radiation exit window may have a first radiation exit window surface area (Al).

Especially, the beam shaping optical element is optically coupled with at least the first radiation exit window, the beam shaping optical element comprising a radiation entrance window configured to receive at least part of the converter light.

Especially, the radiation entrance window has a radiation entrance window surface area. As indicated above, in embodiments wherein a truncated beam shaping element is applied, the radiation entrance window surface area is larger than the first radiation exit window surface area (A2).

As indicated above, the light generating device may comprise a plurality of light sources to provide light source light that is at least partly converted by the light transmissive body, more especially the luminescent material of the light transmissive body, into converter radiation. The converted light can at least partially escape form the first radiation exit window, which is especially in optical contact with the optical element, more especially the radiation entrance window thereof.

The optical element may especially comprises a collimator used to convert (to “collimate”) the light beam into a beam having a desired angular distribution. Further, the optical element especially comprises a light transmissive body comprising the radiation entrance window. Hence, the optical element may be a body of light transmissive material that is configured to collimate the converter radiation from the luminescent body.

In specific embodiments, the optical element comprises a compound parabolic like collimator, such as a CPC (compound parabolic concentrator).

A massive collimator, such as a massive CPC, may especially be used as extractor of light and to collimate the (emission) radiation. Alternatively, one may also configured a dome with optical contact (n>l .00) on the nose of the rod or a hollow collimator, such as a CPC, to concentrate the (emission) radiation.

The optical element may have cross section (perpendicular to an optical axis) with a shape that is the same as the cross-section of the luminescent body (perpendicular to the longest body axis (which body axis is especially parallel to a radiation input face). For instance, would the latter have a rectangular cross section, the former may also have such rectangular cross section, though the dimension may be different. Further, the dimension of the optical element may vary over its length (as it may have a beam shaping function).

Further, the shape of the cross-section of the optical element may vary with position along the optical axis. In a specific configuration, the aspect ratio of a rectangular cross-section may change, preferably monotonically, with position along the optical axis. In another preferred configuration, the shape of the cross-section of the optical element may change from round to rectangular, or vice versa, with position along the optical axis.

As indicated above, first radiation exit window (of the elongated light transmissive body) is in optical contact with the radiation entrance window of the optical element. The term“optical contact” and similar terms, such as“optically coupled” especially mean that the light escaping the first radiation exit window surface area (Al) may enter the optical element radiation entrance window with minimal losses (such as Fresnel reflection losses or TIR (total internal reflection) losses) due to refractive index differences of these elements. The losses may be minimized by one or more of the following elements: a direct optical contact between the two optical elements, providing an optical glue between the two optical elements, preferably the optical glue (adhesive material) having a refractive index higher that the lowest refractive index of the two individual optical elements, providing the two optical elements in close vicinity (e.g. at a distance much smaller than the wavelength of the light), such that the light will tunnel through the material present between the two optical elements, providing an optically transparent interface material between the two optical elements, preferably the optically transparent interface material having a refractive index higher that the lowest refractive index of the two individual optical elements, the optically transparent interface material might be a liquid or a gel or providing optical Anti Reflection coatings on the surfaces of (one or both of) the two individual optical elements. In embodiments, the optically transparent interface material may also be a solid material.

Further, the optical interface material or glue especially may have a refractive index not higher than the highest refractive index of the two individual optical elements. Instead of the term“in optical contact” also the terms“radiationally coupled” or“radiatively coupled” may be used. The term "radiationally coupled" especially means that the luminescent body (i.e. the elongated light transmissive body) and the optical element are associated with each other so that at least part of the radiation emitted by the luminescent body is received by the luminescent material. The luminescent body and the optical element, especially the indicated“windows” may in embodiments be in physical contact with each other or may in other embodiments be separated from each other with a (thin) layer of optical glue, e.g. having a thickness of less than about 1 mm, preferably less than 100 pm. When no optically transparent interface material is applied, the distance between two elements being in optical contact may especially be about at maximum the wavelength of relevance, such as the wavelength of an emission maximum. For visible wavelengths, this may be less than 1 pm, such as less than 0.7 pm, and for blue even smaller, such as at maximum 0.5 pm (see also above).

Likewise, the light sources are radiationally coupled with the luminescent body, though in general the light sources are not in physical contact with the luminescent body (see also below). As the luminescent body is a body and as in general also the optical element is a body, the term“window” herein may especially refer to side or a part of a side. Hence, the luminescent body comprises one or more side faces, wherein the optical element is configured to receive at the radiation entrance window at least part of the converter radiation that escapes from the one or more side faces.

This radiation may reach the entrance window via a gas, such as air directly. Additionally or alternatively, this radiation may reach the entrance window after one or more reflections, such as reflections at a mirror positioned nearby the luminescent body. Hence, in embodiments the light generating device may further comprise a first reflective surface, especially configured parallel to one or more side faces, and configured at a first distance from the luminescent body, wherein the first reflective surface is configured to reflect at least part of the converter radiation that escapes from the one or more side faces back into the luminescent body or to the optical element. The space between the reflective surface and the one or more side faces comprises a gas, wherein the gas comprises air. The first distance may e.g. be in the range of 0.1 pm - 20 mm, such as in the range of 1 pm - 10 mm, like 2 pm - 10 mm.

Especially, the distance is at least wavelength of interest, more especially at least twice the wavelength of interest. Further, as there may be some contact, e.g. for holding purposes or for distance holder purposes, especially an average distance is at least l,, such as at least 1.5* h like at least 2* h such as especially about 5* h wherein h is the wavelength of interest. Especially, however, the average distance is in embodiments not larger than 50 pm, such as not larger than 25 pm, like not larger than 20 pm, like not larger than 10 pm, for purposes of good thermal contact. Likewise, such average minimum distance may apply to a reflector and/or optical filter configured at e.g. an end face, or other optical components as well. Optionally, in embodiments an element may comprise both heat sinking function a reflection function, such as a heat sink with a reflective surface, or a reflector functionally coupled to a heat sink.

The light generating device may be configured to provide blue, green, yellow, orange, or red light, etc.. Alternatively or additionally, in embodiments, the light generating device may (also) be configured to provide one or more of UV, such as near UV (especially in the range of 320-400 nm), and IR, such as near IR (especially in the range of 750-3000 nm). Further, in specific embodiment, the light generating device may be configured to provide white light. If desired, monochromaticity may be improved using optical filter(s). The definitions of near UV and near infrared may partly overlap with the generally used definition for visible light, which is 380-780 nm.

The term“light concentrator” or“luminescent concentrator” is herein used, as one or more light sources irradiate a relative large surface (area) of the light converter, and a lot of converter radiation may escape from a relatively small area (exit window) of the light converter. Thereby, the specific configuration of the light converter provides its light concentrator properties. Especially, the light concentrator may provide Stokes-shifted light, which is Stokes shifted relative to the pump radiation. Hence, the term“luminescent concentrator” or“luminescent element” may refer to the same element, especially an elongated light transmissive body (comprising a luminescent material), wherein the term “concentrator” and similar terms may refer to the use in combination with one or more light sources and the term“element” may be used in combination with one or more, including a plurality, of light sources. When using a single light source, such light source may e.g. be a laser, especially a solid state laser (like a LED laser). The elongated light transmissive body comprises a luminescent material and can herein especially be used as luminescent concentrator. The elongated light transmissive body is herein also indicated as“luminescent body”. Especially, a plurality of light sources, such as a plurality of solid state light sources, may be applied.

The terms“upstream” and“downstream” relate to an arrangement of items or features relative to the propagation of the light from a light generating means (here the especially the light source(s)), wherein relative to a first position within a beam of light from the light generating means, a second position in the beam of light closer to the light generating means is“upstream”, and a third position within the beam of light further away from the light generating means is“downstream”.

The light concentrator comprises a light transmissive body. The light concentrator is especially described in relation to an elongated light transmissive body, such as a ceramic rod or a crystal, such as a single crystal. However, these aspects may also be relevant for other shaped ceramic bodies or single crystals. In specific embodiments, the luminescent body comprises a ceramic body or single crystal.

The light transmissive body has light guiding or wave guiding properties. Hence, the light transmissive body is herein also indicated as waveguide or light guide. As the light transmissive body is used as light concentrator, the light transmissive body is herein also indicated as light concentrator. The light transmissive body will in general have (some) transmission of one or more of (N)UV, visible and (N)IR radiation, such as in embodiments at least visible light, in a direction perpendicular to the length of the light transmissive body. Without the activator (dopant) such as trivalent cerium, the internal transmission in the visible might be close to 100%.

The transmission of the light transmissive body for one or more luminescence wavelengths may be at least 80%/cm, such as at least 90%/cm, even more especially at least 95%/cm, such as at least 98%/cm, such as at least 99%/cm. This implies that e.g. a 1 cm³ cubic shaped piece of light transmissive body, under perpendicular irradiation of radiation having a selected luminescence wavelength (such as a wavelength corresponding to an emission maximum of the luminescence of the luminescent material of the light transmissive body), will have a transmission of at least 95%.

Herein, values for transmission especially refer to transmission without taking into account Fresnel losses at interfaces (with e.g. air). Hence, the term“transmission” especially refers to the internal transmission. The internal transmission may e.g. be determined by measuring the transmission of two or more bodies having a different width over which the transmission is measured. Then, based on such measurements the contribution of Fresnel reflection losses and (consequently) the internal transmission can be determined. Hence, especially, the values for transmission indicated herein, disregard Fresnel losses.

In addition to a high transmission for the wavelength(s) of interest, also the scattering for the wavelength(s) may especially be low. Hence, the mean free path for the wavelength of interest only taking into account scattering effects (thus not taking into account possible absorption (which should be low anyhow in view of the high transmission), may be at least 0.5 times the length of the body, such as at least the length of the body, like at least twice the length of the body. For instance, in embodiments the mean free path only taking into account scattering effects may be at least 5 mm, such as at least 10 mm. The wavelength of interest may especially be the wavelength at maximum emission of the luminescence of the luminescent material. The term“mean free path” is especially the average distance a ray will travel before experiencing a scattering event that will change its propagation direction.

The terms“light” and“radiation” are herein interchangeably used, unless clear from the context that the term“light” only refers to visible light. The terms“light” and “radiation” may thus refer to UV radiation, visible light, and IR radiation. In specific embodiments, especially for lighting applications, the terms“light” and“radiation” refer to visible light.

The term UV radiation may in specific embodiments refer to near UV radiation (NUV). Therefore, herein also the term“(N)UV” is applied, to refer to in general UV, and in specific embodiments to NUV. The term IR radiation may in specific

embodiments refer to near IR radiation (NIR). Therefore, herein also the term“(N)IR” is applied, to refer to in general IR, and in specific embodiments to NIR.

Herein, the term“visible light” especially relates to light having a wavelength selected from the range of 380-780 nm. The transmission can be determined by providing light at a specific wavelength with a first intensity to the light transmissive body under perpendicular radiation and relating the intensity of the light at that wavelength measured after transmission through the material, to the first intensity of the light provided at that specific wavelength to the material (see also E-208 and E-406 of the CRC Handbook of Chemistry and Physics, 69th edition, 1088-1989).

The light transmissive body may have any shape, such as beam (or bar) like or rod like, however especially beam like (cuboid like). However, the light transmissive body may also be disk like, etc. The light transmissive body, such as the luminescent concentrator, might be hollow, like a tube, or might be filled with another material, like a tube filled with water or a tube filled with another solid light transmissive medium. The invention is not limited to specific embodiments of shapes, neither is the invention limited to embodiments with a single exit window or outcoupling face. Below, some specific embodiments are described in more detail. Would the light transmissive body have a circular cross-section, then the width and height may be equal (and may be defined as diameter). Especially, however, the light transmissive body has a cuboid like shape, such as a bar like shape, and is further configured to provide a single exit window.

In a specific embodiment, the light transmissive body may especially have an aspect ratio larger than 1, i.e. the length is larger than the width. In general, the light transmissive body is a rod, or bar (beam), or a rectangular plate, though the light transmissive body does not necessarily have a square, rectangular or round cross-section. In general, the light source is configured to irradiate one (or more) of the longer faces (side edge), herein indicated as radiation input face, and radiation escapes from a face at a front (front edge), herein indicated as radiation exit window. The light source(s) may provide radiation to one or more side faces, and optionally an end face. Hence, there may be more than one radiation input face.

Especially, in embodiments the solid state light source, or other light source, is not in (direct) physical contact with the light transmissive body.

Physical contact (between the light exit window(s) of the light source(s) and the light entrance window(s) of the light transmissive body/bodies) may lead to undesired outcoupling (from the light transmissive body) and thus a reduction in concentrator efficiency. Hence, especially there is substantially no physical contact. If the actual contact area is kept small enough, the optical impact may be negligible or at least acceptable.

Therefore, it may be perfectly acceptable to have some physical contact, e.g. by some small points as resulting from a certain surface roughness, or non-perfectly flat surface, or by some intentionally created“highest spots” on a surface that will define a certain average distance between the two surfaces that don’t extract substantial amounts of light while enabling a short average distance.

Further, in general the light transmissive body comprises two substantially parallel faces, a radiation input face and opposite thereof the opposite face. These two faces define herein the width of the light transmissive body. In general, the length of these faces defines the length of the light transmissive body. However, as indicated above, and also below, the light transmissive body may have any shape, and may also include combinations of shapes. Especially, the radiation input face has an radiation input face area (A), wherein the radiation exit window has a radiation exit window area (E), and wherein the radiation input face area (A) is at least 1.5 times, even more especially at least two times larger than the radiation exit window area (E), especially at least 5 times larger, such as in the range of 2- 50,000, especially 5-5,000 times larger. Hence, especially the elongated light transmissive body comprises a geometrical concentration factor, defined as the ratio of the area of the radiation input faces and the area of the radiation exit window, of at least 1.5, such as at least 2, like at least 5, or much larger (see above). This allows e.g. the use of a plurality of solid state light sources (see also below). For typical applications like in automotive, digital projectors, or high brightness spot light applications, a small but high radiant flux or luminous flux emissive surface is desired. This cannot be obtained with a single LED, but can be obtained with the present light generating device. Especially, the radiation exit window has a radiation exit window area (E) selected from the range of 1-100 mm². With such dimensions, the emissive surface can be small, whereas nevertheless high radiance or luminance may be achieved. As indicated above, the light transmissive body in general has an aspect ratio (of length/width). This allows a small radiation exit surface, but a large radiation input surface, e.g. irradiated with a plurality of solid state light sources. In a specific embodiment, the light transmissive body has a width (W) selected from the range of 0.5-100 mm, such as 0.5-10 mm. The light transmissive body is thus especially an integral body, having the herein indicated faces.

The generally rod shaped or bar shaped light transmissive body can have any cross sectional shape, but in embodiments has a cross section the shape of a square, rectangle, round, oval, triangle, pentagon, or hexagon. Generally the ceramic or crystal bodies are cuboid. In specific embodiments, the body may be provided with a different shape than a cuboid, with the light input surface having somewhat the shape of a trapezoid. By doing so, the light flux may be even enhanced, which may be advantageous for some applications. Hence, in some instances (see also above) the term“width” may also refer to diameter, such as in the case of a light transmissive body having a round cross section. Hence, in

embodiments the elongated light transmissive body further has a width (W) and a height (H), with especially L>W and L>H. Especially, the first face and the second face define the length, i.e. the distance between these faces is the length of the elongated light transmissive body. These faces may especially be arranged parallel. Further, in a specific embodiment the length (L) is at least 2 cm, like 3-20 cm, such as 4-20 cm, such as at maximum 15 cm. Other dimensions may, however, also be possible, such as e.g. 0.5-2 cm.

Especially, the light transmissive body has a width (W) selected to absorb more than 95% of the light source light. In embodiments, the light transmissive body has a width (W) selected from the range of 0.03-4 cm, especially 0.05-2 cm, such as 0.1 -1.5 cm, like 0.1-1 cm. With the herein indicated cerium concentration, such width is enough to absorb substantially all light (especially at the excitation wavelength with maximum excitation intensity) generated by the light sources. The light transmissive body may also be a cylindrically shaped rod. In embodiments the cylindrically shaped rod has one flattened surface along the longitudinal direction of the rod and at which the light sources may be positioned for efficient incoupling of light emitted by the light sources into the light transmissive body. The flattened surface may also be used for placing heatsinks. The cylindrical light transmissive body may also have two flattened surfaces, for example located opposite to each other or positioned perpendicular to each other. In embodiments the flattened surface extends along a part of the longitudinal direction of the cylindrical rod. Especially however, the edges are planar and configured perpendicular to each other.

The side face is especially such flattened surface(s). The flattened surface especially has a relatively low surface roughness, such as an Ra of at maximum 100 nm, such as in the range of 5-100 nm, like up to 50 nm.

The light transmissive body may also be a fiber or a multitude of fibers, for instance a fiber bundle, either closely spaced or optically connected in a transparent material. The fiber may be referred to as a luminescent fiber. The individual fiber may be very thin in diameter, for instance, 0.1 to 0.5 mm. The light transmissive body may also comprise a tube or a plurality of tubes. In embodiments, the tube (or tubes) may be filled with a gas, like air or another gas having higher heat conductivity, such as helium or hydrogen, or a gas comprising two or more of helium, hydrogen, nitrogen, oxygen and carbon dioxide. In embodiments, the tube (or tubes) may be filled with a liquid, such as water or (another) cooling liquid.

The light transmissive body as set forth below in embodiments according to the invention may also be folded, bended and/or shaped in the length direction such that the light transmissive body is not a straight, linear bar or rod, but may comprise, for example, a rounded comer in the form of a 90 or 180 degrees bend, a U-shape, a circular or elliptical shape, a loop or a 3-dimensional spiral shape having multiple loops. This provides for a compact light transmissive body of which the total length, along which generally the light is guided, is relatively large, leading to a relatively high lumen output, but can at the same time be arranged into a relatively small space. For example luminescent parts of the light transmissive body may be rigid while transparent parts of the light transmissive body are flexible to provide for the shaping of the light transmissive body along its length direction. The light sources may be placed anywhere along the length of the folded, bended and/or shaped light transmissive body. Parts of the light transmissive body that are not used as light incoupling area or light exit window may be provided with a reflector. Hence, in an embodiment the light generating device further comprises a reflector configured to reflect luminescent material radiation back into the light transmissive body. Therefore, the light generating device may further include one or more reflectors, especially configured to reflect radiation back into the light transmissive body that escapes from one or more other faces than the radiation exit window. Especially, a face opposite of the radiation exit window may include such reflector, though in an embodiment not in physical contact therewith. Hence, the reflectors may especially not be in physical contact with the light transmissive body. Therefore, in an embodiment the light generating device further comprises an optical reflector (at least) configured downstream of the first face and configured to reflect light back into the elongated light transmissive body. Alternatively or additionally, optical reflectors may also be arranged at other faces and/or parts of faces that are not used to couple light source light in or luminescence light out. Especially, such optical reflectors may not be in physical contact with the light transmissive body. Further, such optical reflector(s) may be configured to reflect one or more of the luminescence and light source light back into the light transmissive body. Hence, substantially all light source light may be reserved for conversion by the luminescent material (i.e. the activator element(s) such as especially Ce³⁺) and a substantial part of the luminescence may be reserved for outcoupling from the radiation exit window. The term “reflector” may also refer to a plurality of reflectors.

The one or more reflectors may consist of a metal reflector, such as a thin metal plate or a reflective metal layer deposited on a substrate, such as e.g. glass. The one or more reflectors may consist of an optical transparent body containing optical structure to reflect (part) of the light such as prismatic structures. The one or more reflectors may consist of specular reflectors. The one or more reflectors may contain microstructures, such as prism structures or saw tooth structures, designed to reflect the light rays towards a desired direction.

Preferably, such reflectors are also present in the plane where the light sources are positioned, such that that plane consist of a mirror having openings, each opening having the same size as a corresponding light source allowing the light of that corresponding light source to pass the mirror layer and enter the elongated (first) light transmissive body while light that traverses from the (first) light transmissive body in the direction of that plane receives a high probability to hit the mirror layer and will be reflected by that mirror layer back towards the (first) light transmissive body. The terms“coupling in” and similar terms and“coupling out” and similar terms indicate that light changes from medium (external from the light transmissive body into the light transmissive body, and vice versa, respectively). In general, the light exit window will be a face (or a part of a face), configured (substantially) perpendicular to one or more other faces of the waveguide. In general, the light transmissive body will include one or more body axes (such as a length axis, a width axis or a height axis), with the exit window being configured (substantially) perpendicular to such axis. Hence, in general, the light input face(s) will be configured (substantially) perpendicular to the light exit window. Thus, the radiation exit window is especially configured perpendicular to the one or more radiation input faces. Therefore, especially the face comprising the light exit window does not comprise a light input face.

For further improving efficiency and/or for improving the spectral distribution several optical elements may be included like mirrors, optical filters, additional optics, etc.

In specific embodiments, the light generating device may have a mirror configured at the first face configured to reflect light back into the elongated light

transmissive body, and/or may have one or more of an optical filter, a (wavelength selective) mirror, a reflective polarizer, light extraction structures, and a collimator configured at the second face. At the second face the mirror may e.g. be a wavelength selective mirror or a mirror including a hole. In the latter embodiment, light may be reflected back into the body but part of the light may escape via the hole. Especially, in embodiments the optical element may be configured at a distance of about 0.01-1 mm, such as 0.1-1 mm from the body. This may especially apply for e.g. mirrors, wherein optical coupling is not desired.

When optical coupling is desired, such as with an optical element, like a CPC or a mixing element, downstream of the (part of the) body where the luminescent material is located, an optically transparent interface material may be applied. In yet other embodiments, when no optically transparent interface material is applied, the average distance between two elements being in optical contact may especially be about at maximum the wavelength of relevance, such as the wavelength of an emission maximum. Hence, when optical contact is desired, there may be physical contact. Even in such embodiments, there may be a non-zero average distance, but then equal to or lower than the wavelength of interest.

In specific embodiments, especially when no optical contact is desired, the average distance may be as indicated above but at a few places, for instance for configuration purposes, there may be physical contact. For instance, there may be contact with the edge faces over less than 10%, such as over less than 5% of the total area of the side faces. Hence, the minimum average distance may be as defined e.g. above and if there is physical contact, this physical contact may be with at maximum 10% of the surface area of the surface with which the element (mirror and/or heat sink) is in physical contact, such as at maximum 5%, like at maximum 2%, even more especially at maximum 1%. For instance, for the side faces an average distance may e.g. be between ca 2 and 10 pm (the lower limit basically determined as being a few times the wavelength of interest; here, assuming e.g. visible light). This may be achieved by having physical contact (to secure that distance) over less than 1% of the total area of that respective side face.

For instance, a heat sink or a reflector, or the relevant surface may have some protrusions, like a surface roughness, by which there may be contact between the surface and the element, but in average the distance is at least l; (or more, see also above)(in order to essentially prevent optical contact), but there is physical contact with equal to or less than 10% of the surface of the body (to which the element may be thermally coupled and/or optically not coupled), especially substantially less.

In embodiments, optical elements may be included at one or more of the side faces. In particular, anti-reflection coatings may be applied to enhance coupling efficiency of the (excitation) light source light and/or (wavelength selective) reflection coatings for the converted light.

Downstream of the radiation exit window, optionally an optical filter may be arranged. Such optical filter may be used to remove undesired radiation. For instance, when the light generating device should provide red light, all light other than red may be removed. Hence, in a further embodiment the light generating device further comprises an optical filter configured downstream of the radiation exit window and configured to reduce the relative contribution of undesired light in the converter radiation (downstream of the radiation exit window). For filtering out light source light, optionally an interference filter may be applied.

In yet a further embodiment, the light generating device further comprises a collimator configured downstream of the radiation exit window (of the highest order luminescent concentrator) and configured to collimate the converter radiation. Such collimator, like e.g. a CPC (compound parabolic concentrator), may be used to collimate the light escaping from the radiation exit window and to provide a collimated or pre-collimated beam of light. Herein, the terms“collimated”,“precollimated” and similar terms may especially refer to a light beam having a solid angle (substantially) smaller than 2p.

As indicated above, the light generating device may comprise a plurality of light sources. These plurality of light sources may be configured to provide light source light to a single side or face or to a plurality of faces; see further also below. When providing light to a plurality of faces, in general each face will receive light of a plurality of light sources (a subset of the plurality of light sources). Hence, in embodiments a plurality of light sources will be configured to provide light source light to a radiation input face. Also this plurality of light sources will in general be configured in a row or a plurality of rows. Hence, the light transmissive body is elongated, the plurality of light sources may be configured in a row, which may be substantially parallel to the axis of elongated of the light transmissive body. The row of light sources may have substantially the same length as the elongated light transmissive body. Hence, in the light transmissive body has a length (L) in the range of about 80-120% of the second length (L2) of the row of light sources; or the row of light sources has a length in the range of about 80-120% of the length of the light transmissive body.

The light sources may be configured to provide light with a wavelength selected from the range of UV (including near UV), visible, and infrared (including near IR).

Especially, the light sources are light sources that during operation emit (light source light) at least light at a wavelength selected from the range of 200-490 nm, especially light sources that during operation emit at least light at wavelength selected from the range of 360-490 nm, such as 400-490 nm, even more especially in the range of 430-490 nm, such as 440-490 nm, such as at maximum 480 nm. This light may partially be used by the

luminescent material. Hence, in a specific embodiment, the light source is configured to generate blue light. In a specific embodiment, the light source comprises a solid state light source (such as a LED or laser diode). The term“light source” may also relate to a plurality of light sources, such as e.g. 2-2000, such as 2-500, like 2-100, e.g. at least 4 light sources, such as in embodiments especially 4-80 (solid state) light sources, though many more light sources may be applied. Hence, in embodiments 4-500 light sources may be applied, like e.g. 8-200 light sources, such as at least 10 light sources, or even at least 50 light sources. The term“light source” may also relate to one or more light sources that are tailored to be applied for such light concentrating luminescent concentrators, e.g. one or more LED’s having a long elongated radiating surface matching the long elongated light input surfaces of the elongated luminescent concentrator. Hence, the term LED may also refer to a plurality of LEDs. Hence, as indicated herein, the term“solid state light source” may also refer to a plurality of solid state light sources. In an embodiment (see also below), these are substantially identical solid state light sources, i.e. providing substantially identical spectral distributions of the solid state light source radiation. In embodiments, the solid state light sources may be configured to irradiate different faces of the light transmissive body. Further, the term“light source” may in embodiments also refer to a so-called chips-on-board (COB) light source. The term“COB” especially refers to LED chips in the form of a semiconductor chip that is neither encased nor connected but directly mounted onto a substrate, such as a PCB (“printed circuit board”) or comparable. Hence, a plurality of semiconductor light sources may be configured on the same substrate. In embodiments, a COB is a multi LED chip configured together as a single lighting module.

The light generating device comprises a plurality of light sources. Especially, the light source light of the plurality (m) of light sources have spectral overlap, even more especially, they are of the same type and provide substantial identical light (having thus substantial the same spectral distribution). Hence, the light sources may substantially have the same emission maximum (“peak maximum”), such as within a bandwidth of 10 nm, especially within 8 nm, such as within 5 nm (e.g. obtained by binning). However, in yet other embodiments, the light generating device may comprise a single light source, especially a solid state light source having a relatively large die. Hence, herein also the phrase“one or more light sources” may be applied.

In embodiments, there may be two or more different luminescent materials, such as e.g. when applying two or more different light transmissive bodies. In such embodiments, the light sources may comprise light sources with two or more different emission spectra enabling excitation of two different luminescent materials. Such two or more different light sources may belong to different bins.

The light sources are especially configured to provide a blue optical power (W_0pt) of at least 0.2 Watt/mm² to the light transmissive body, i.e. to the radiation input face(s). The blue optical power is defined as the energy that is within the energy range that is defined as blue part of the spectrum (see also below). Especially, the photon flux is in average at least 4.5* 10¹⁷ photons/(s.mm²), such as at least 6.0* 10¹⁷ photons/(s.mm²).

Assuming blue (excitation) light, this may e.g. correspond to a blue power (W_opt) provided to at least one of the radiation input faces of in average at least 0.067 Watt/mm² and 0.2 Watt/mm², respectively. Here, the term“in average” especially indicates an average over the area (of the at least one of the radiation input surfaces). When more than one radiation input surface is irradiated, then especially each of these radiation input surfaces receives such photon flux. Further, especially the indicated photon flux (or blue power when blue light source light is applied) is also an average over time. In yet a further embodiment, especially for (DLP (digital light processing)) projector applications, the plurality of light sources are operated in pulsed operation, such as with a duty cycle selected from the range of 10-80%, such as 25-70%.

In yet a further embodiment, especially for (LCD or DLP) projector applications using dynamic contrast technologies, such as e.g. described in WOO 119092 or USRE42428 (El), the plurality of light sources are operated in video signal content controlled PWM pulsed operation with a duty cycle selected from the range of 0.01-80%, such as 0.1-70%.

In yet a further embodiment, especially for (LCD or DLP) projector applications using dynamic contrast technologies, such as e.g. described in US patent WO0119092 or US6631995 (B2), the plurality of light sources are operated in video signal content controlled intensity modulated operation with intensity variations selected from the range of 0.1-100%, such as 2-100%.

The light generating device may comprise a plurality of luminescent concentrators, such as in the range of 2-50, like 2-20 light concentrators (which may e.g. be stacked).

The light concentrator may radiationally be coupled with one or more light sources, especially a plurality of light sources, such as 2-1000, like 2-50 light sources. The term "radiationally coupled" especially means that the light source and the light concentrator are associated with each other so that at least part of the radiation emitted by the light source is received by the light concentrator (and at least partly converted into luminescence). Instead of the term“luminescence” also the terms“emission” or“emission radiation” may be applied.

Hence, the luminescent concentrator receives at one or more radiation input faces radiation (pump radiation) from an upstream configured light concentrator or from upstream configured light sources. Further, the light concentrator comprises a luminescent material configured to convert at least part of a pump radiation received at one or more radiation input faces into luminescent material radiation, and the luminescent concentrator configured to couple at least part of the luminescent material radiation out at the radiation exit window as converter radiation. This converter radiation is especially used as component of the light generating device light.

The phrase“configured to provide luminescent material radiation at the radiation exit window” and similar phrases especially refers to embodiments wherein the luminescent material radiation is generated within the luminescent concentrator (i.e. within the light transmissive body), and part of the luminescent material radiation will reach the radiation exit window and escape from the luminescent concentrator. Hence, downstream of the radiation exit window the luminescent material radiation is provided. The converter radiation, downstream of the radiation exit window comprises at least the luminescent material radiation escaped via the radiation exit window from the light converter. Instead of the term“converter radiation” also the term“light concentrator light” may be used. Pump radiation can be applied to a single radiation input face or a plurality of radiation input faces.

In embodiments, the length (L) is selected from the range of 1-100 cm, such as especially 2-50 cm, like at least 3 cm, such as 5-50 cm, like at maximum 30 cm. This may thus apply to all luminescent concentrators. However, the range indicates that the different luminescent concentrators may have different lengths within this range.

In yet further embodiments, the elongated light transmissive body (of the luminescent concentrator) comprises an elongated ceramic body. For instance, luminescent ceramic garnets doped with Ce³⁺ (trivalent cerium) can be used to convert blue light into light with a longer wavelength, e.g. within the green to red wavelength region, such as in the range of about 500-750 nm, or even in the cyan. To obtain sufficient absorption and light output in desired directions, it is advantageous to use transparent rods (especially substantially shaped as beams). Such rod can be used as light concentrator, converting light source light into converter radiation and providing at an exit surface (a substantial amount of) (concentrated) converter radiation. Light generating devices based on light concentrators may e.g. be of interest for projector applications. For projectors, red, yellow, green and blue luminescent concentrators are of interest. Green and/or yellow luminescent rods, based on garnets, can be relatively efficient. Such concentrators are especially based on YAG:Ce (i.e. Y AFO^CY ) or LuAG, which can be indicated as (Yi-_xLu_x)₃Al₅0i₂:Ce³⁺, where 0<x<l, such as in embodiments Lu₃Al₅0i₂:Ce³⁺.‘Red’ garnets can be made by doping a YAG-gamet with Gd (“YGdAG”). Cyan emitters can be made by e.g. replacing (part of the) Al (in e.g. LuAG) by Ga (to provide“LuGaAG”). Blue luminescent concentrators can be based on YSO

(Y₂Si0₅:Ce³⁺) or similar compounds or BAM (BaMgAhoOi₇:Eu²⁺) or similar compounds, especially configured as single crystal(s). The term similar compounds especially refer to compounds having the same crystallographic structure but where one or more cations are at least partially replaced with another cation (e.g. Y replacing with Lu and/or Gd, or Ba replacing with Sr). Optionally, also anions may be at least partially replaced, or cation-anion combinations, such as replacing at least part of the Al-0 with Si-N. Hence, especially the elongated light transmissive body comprises a ceramic material configured to wavelength convert at least part of the (blue) light source light into converter radiation in e.g. one or more of the green, yellow and red, which converter radiation at least partly escapes from the radiation exit window.

In embodiments, the ceramic material especially comprises an A BsO^CY ceramic material (“ceramic garnet”), wherein A comprises yttrium (Y) and/or lutetium (Lu) and/or gadolinium (Gd), and wherein B comprises aluminum (Al) and/or gallium (Ga), especially at least Al. As further indicated below, A may also refer to other rare earth elements and B may include Al only, but may optionally also include gallium. The formula A₃B₅O i₂:Ce³⁺ especially indicates the chemical formula, i.e. the stoichiometry of the different type of elements A, B and O (3:5:12). However, as known in the art the compounds indicated by such formula may optionally also include a small deviation from stoichiometry.

In yet a further aspect, the invention also provides such elongated light transmissive body per se, i.e. an elongated light transmissive body having a first face and a second face, these faces especially defining the length (L) of the elongated light transmissive body, the elongated light transmissive body comprising one or more radiation input faces and a radiation exit window, wherein the second face comprises the radiation exit window, wherein the elongated light transmissive body comprises a ceramic material configured to wavelength convert at least part of (blue) light source light into converter radiation, such as (at least) one or more of green, yellow, and red converter radiation (which at least partly escapes from the radiation exit window when the elongated light transmissive body is irradiated with blue light source light), wherein the ceramic material comprises an

A₃B₅O i₂:Ce³⁺ ceramic material as defined herein. Such light transmissive body can thus be used as light converter. Especially, such light transmissive body has the shape of a cuboid.

As indicated above, in embodiments the ceramic material comprises a garnet material. However, also other (crystallographic) cubic systems may be applied. Hence, the elongated body especially comprises a luminescent ceramic. The garnet material, especially the ceramic garnet material, is herein also indicated as“luminescent material”. The luminescent material comprises an A₃B₅0i₂:Ce³⁺ (garnet material), wherein A is especially selected from the group consisting of Sc, Y, Tb, Gd, and Lu (especially at least Y and/or Lu, and optionally Gd), wherein B is especially selected from the group consisting of Al and Ga (especially at least Al). More especially, A (essentially) comprises (i) lutetium (Lu), (ii) yttrium, (iii) yttrium (Y) and lutetium (Lu), (iv) gadolinium (Gd), optionally in combination with one of the aforementioned, and B comprises aluminum (Al) or gallium (Ga) or a combination of both. Such garnet is be doped with cerium (Ce), and optionally with other luminescent species such as praseodymium (Pr).

As indicated above, the element A may especially be selected from the group consisting of yttrium (Y) and gadolinium (Gd). Hence, A^BsO^CY especially refers to (Yi_ _xGd_x)₃B₅0i₂:Ce³⁺, wherein especially x is in the range of 0.1-0.5, even more especially in the range of 0.2-0.4, yet even more especially 0.2-0.35. Hence, A may comprise in the range of 50-90 atom %Y, even more especially at least 60-80 atom %Y, yet even more especially 65- 80 atom % of A comprises Y. Further, A comprises thus especially at least 10 atom % Gd, such as in the range of 10-50 atom% Gd, like 20-40 atom%, yet even more especially 20-35 atom % Gd.

Especially, B comprises aluminum (Al), however, B may also partly comprise gallium (Ga) and/or scandium (Sc) and/or indium (In), especially up to about 20% of Al, more especially up to about 10 % of Al may be replaced (i.e. the A ions essentially consist of 90 or more mole % of Al and 10 or less mole % of one or more of Ga, Sc and In); B may especially comprise up to about 10% gallium. Therefore, B may comprise at least 90 atom % Al. Hence, A₃B₅0i₂:Ce³⁺ especially refers to (Yi-_xGd_x)₃Al₅0i₂:Ce³⁺, wherein especially x is in the range of 0.1 -0.5, even more especially in the range of 0.2-0.4.

In another variant, B (especially Al) and O may at least partly be replaced by Si and N. Optionally, up to about 20 % of Al-0 may be replaced by Si-N, such as up to 10%.

For the concentration of cerium, the indication n mole % Ce indicates that n% of A is replaced by cerium. Hence, A₃B₅0i₂:Ce³⁺ may also be defined as (Ai__nCe_n)₃B₅0i₂, with n being in the range of 0.001-0.035, such as 0.0015-0.01. Therefore, a garnet essentially comprising Y and mole Ce may in fact refer to ((Yi-_xGd_x)i-_nCe_n)₃B₅0i₂, with x and n as defined above.

Especially, the ceramic material is obtainable by a sintering process and/or a hot pressing process, optionally followed by an annealing in an (slightly) oxidizing atmosphere. The term“ceramic” especially relates to an inorganic material that is - amongst others - obtainable by heating a (poly crystalline) powder at a temperature of at least 500 °C, especially at least 800 °C, such as at least 1000 °C, like at least 1400 °C, under reduced pressure, atmospheric pressure or high pressure, such as in the range of 10 ⁸ to 500 MPa, such as especially at least 0.5 MPa, like especially at least 1 MPa, like 1 to about 500 MPa, such as at least 5 MPa, or at least 10 MPa, especially under uniaxial or isostatic pressure, especially under isostatic pressure. A specific method to obtain a ceramic is hot isostatic pressing (HIP), whereas the HIP process may be a post-sinter HIP, capsule HIP or combined sinter-HIP process, like under the temperature and pressure conditions as indicate above. The ceramic obtainable by such method may be used as such, or may be further processed (like polishing). A ceramic especially has density that is at least 90% (or higher, see below), such as at least 95%, like in the range of 97-100 %, of the theoretical density (i.e. the density of a single crystal). A ceramic may still be poly crystalline, but with a reduced, or strongly reduced volume between grains (pressed particles or pressed agglomerate particles). The heating under elevated pressure, such as HIP, may e.g. be performed in an inert gas, such as comprising one or more of N₂ and argon (Ar). Especially, the heating under elevated pressures is preceded by a sintering process at a temperature selected from the range of 1400- 1900 °C, such as 1500-1800 °C. Such sintering may be performed under reduced pressure, such as at a pressure of 10² Pa or lower. Such sintering may already lead to a density of in the order of at least 95%, even more especially at least 99%, of the theoretical density. After both the pre-sintering and the heating, especially under elevated pressure, such as HIP, the density of the light transmissive body can be close to the density of a single crystal. However, a difference is that grain boundaries are available in the light transmissive body, as the light transmissive body is poly crystalline. Such grain boundaries can e.g. be detected by optical microscopy or SEM. Hence, herein the light transmissive body especially refers to a sintered polycrystalline having a density substantially identical to a single crystal (of the same material). Such body may thus be highly transparent for visible light (except for the absorption by the light absorbing species such as especially Ce³⁺).

The luminescent concentrator may also be a crystal, such as a single crystal. Such crystals can be grown / drawn from the melt in a higher temperature process. The large crystal, typically referred to as boule, can be cut into pieces to form the light transmissive bodies. The polycrystalline garnets mentioned above are examples of materials that can alternatively also be grown in single crystalline form.

After obtaining the light transmissive body, the body may be polished. Before or after polishing an annealing process (in an oxidative atmosphere) may be executed, especially before polishing. In a further specific embodiment, the annealing process lasts for at least 2 hours, such as at least 2 hours at least 1200 °C. Further, especially the oxidizing atmosphere comprises for example 0₂.

Instead of cerium doped garnets, or in addition to such garnets, also other luminescent materials may be applied, e.g. embedded in organic or inorganic light transmissive matrixes, as luminescent concentrator. For instance quantum dots and/or organic dyes may be applied and may be embedded in transmissive matrices like e.g. polymers, like PMMA, or polysiloxanes, etc. etc.. Other light transmissive material as host matrix may be used as well, see also below.

Quantum dots are small crystals of semiconducting material generally having a width or diameter of only a few nanometers. When excited by incident light, a quantum dot emits light of a color determined by the size and material of the crystal. Light of a particular color can therefore be produced by adapting the size of the dots. Most known quantum dots with emission in the visible range are based on cadmium selenide (CdSe) with a shell such as cadmium sulfide (CdS) and zinc sulfide (ZnS). Cadmium free quantum dots such as indium phosphode (InP), and copper indium sulfide (CuInS₂) and/or silver indium sulfide (AgInS₂) can also be used. Quantum dots show very narrow emission band and thus they show saturated colors. Furthermore the emission color can easily be tuned by adapting the size of the quantum dots. Any type of quantum dot known in the art may be used in the present invention. However, it may be preferred for reasons of environmental safety and concern to use cadmium- free quantum dots or at least quantum dots having a very low cadmium content.

Instead of quantum dots or in addition to quantum dots, also other quantum confinement structures may be used. The term“quantum confinement structures” should, in the context of the present application, be understood as e.g. quantum wells, quantum dots, quantum rods, or nano-wires.

Organic phosphors can be used as well. Examples of suitable organic phosphor materials are organic luminescent materials based on perylene derivatives, for example compounds sold under the name Lumogen® by BASF. Examples of suitable compounds include, but are not limited to, Lumogen® Red F305, Lumogen® Orange F240, Lumogen® Yellow F083, and Lumogen® F170.

Several color conversion schemes may be possible. Especially, however, the Stokes shift is relatively small. Especially, the Stokes shift, defined as the difference (in wavelength) between positions of the band maxima of the light source used for pumping and the light which is emitted, is not larger than 100 nm; especially however, the Stokes shift is at least about 10 nm, such as at least about 20 nm. This may especially apply to the light source light to first luminescent material radiation conversion, but also apply to the second pump radiation to second luminescent material radiation conversion, etc.

In embodiments, the plurality of light sources are configured to provide UV radiation as first pump radiation, and the luminescent concentrators are configured to provide one or more of blue and green first converter radiation. In yet other embodiments, the plurality of light sources are configured to provide blue radiation as first pump radiation, and the luminescent concentrators are configured to provide one or more of green and yellow first converter radiation. Note, as also indicated below, such embodiments may also be combined.

The light generating device may further comprise a cooling element in thermal contact with the luminescent concentrator. The cooling element can be a heatsink or an actively cooled element, such as a Peltier element. Further, the cooling element can be in thermal contact with the light transmissive body via other means, including heat transfer via air or with an intermediate element that can transfer heat, such as a thermal grease.

Especially, however, the cooling element is in physical contact with the light transmissive body. The term“cooling element” may also refer to a plurality of (different) cooling elements.

Hence, the light generating device may include a heatsink configured to facilitate cooling of the solid state light source and/or luminescent concentrator. The heatsink may comprise or consist of copper, aluminum, silver, gold, silicon carbide, aluminum nitride, boron nitride, aluminum silicon carbide, beryllium oxide, silicon-silicon carbide, aluminum silicon carbide, copper tungsten alloys, copper molybdenum carbides, carbon, diamond, graphite, and combinations of two or more thereof. Alternatively or additionally, the heatsink may comprise or consist of aluminum oxide. The term“heatsink” may also refer to a plurality of (different) heatsink. The light generating device may further include one or more cooling elements configured to cool the light transmissive body. With the present invention, cooling elements or heatsinks may be used to cool the light transmissive body and the same or different cooling elements or heatsinks may be used to cool the light sources. The cooling elements or heatsinks may also provide interfaces to further cooling means or allow cooling transport to dissipate the heat to the ambient. For instance, the cooling elements or heatsinks may be connected to heat pipes or a water cooling systems that are connect to more remotely placed heatsinks or may be directly cooled by air flows such as generated by fans. Both passive and active cooling may be applied.

In specific embodiments, there is no physical contact between the heat sink (or cooling elements) and the light transmissive body. Especially, the average is at least the intensity averaged wavelength of light that is transmitted by luminescence of luminescent material. In embodiments, the average between the light transmissive body and the heatsink or cooling element is at least 1 pm, such as at least 2 pm, like at least 5 pm. Further, for a good heat transfer the average distance between the light transmissive body and the heatsink or cooling elements is not larger than 50 pm, such as not larger than 25 pm, like not larger than 20 pm, such as equal to or smaller than 15 pm, like at maximum 10 pm. Therefore, in embodiments the light generating device may further comprise a heat sink having an average distance to the elongated light transmissive body of at least 1 pm, such as at least 2 pm, like especially at least 5 pm, or wherein the heat dissipating element is in physical contact with at maximum 10%, such as at maximum 5% of a total area of the side face(s) of the elongated light transmissive body. The average is thus especially not larger than 50 pm. Instead of the term“heat sink” also the term cooling element may be applied.

In particular embodiments, the elongated luminescent concentrator is clamped between 2 metal plates or clamped within a housing consisting of a highly thermal conductive material such way that a sufficient air gap between the elongated luminescent concentrator remains present to provide TIR (total internal reflection) of the light trapped within the elongated luminescent concentrator while a sufficient amount of heat may traverse from the elongated luminescent concentrator through the air gap towards the highly thermal conductive housing. The thickness of the air gap is higher than the wavelength of the light, e.g. higher than 0.1 pm, e.g. higher 0.5 pm. The elongated luminescent concentrator is secured in the housing by providing small particles between the elongated luminescent concentrator and the housing, such as small spheres or rods having a diameter higher than 0.1 pm, e.g. higher 0.5 pm, like at least 1 pm, such as at least 5 pm, especially equal to or smaller than 20 pm, such as equal to or smaller than 10 pm (see also above defined average). Alternatively, the elongated luminescent concentrator may be secured in the housing by providing some surface roughness on the surfaces of the highly thermal conductive housing touching the elongated luminescent concentrator, the surface roughness varying over a depth higher than 0.1 pm, e.g. higher 0.5 pm, preferably equal to or smaller than about 10 pm.

The density of such spheres, rods or touch points of a rough surface of the highly thermal conductive housing is relatively very small, such that most of the surface area of the elongated light transmissive body remains untouched securing a high level of TIR reflections within of the light trapped within the elongated light transmissive body.

The light generating device may thus essentially consist of the elongated light transmissive body comprising a luminescent material and one or more, especially a plurality of light sources, which pump the luminescent material to provide luminescent material light, that escapes from a radiation exit window (of an end face (second face)).

Further, the light generating device may comprise one or more holding elements for holding the light transmissive body. Especially, these holding elements have contact with the edge faces, but only with a small part thereof to minimize losses of light. For instance, the holding element(s), like clamping device (s) have contact with the edge faces over less than 10%, such as over less than 5% of the total area of the side faces. Further, the light generating device may comprise a heat sink and/or a cooling element. The holding element(s) may be comprised by the heat sink and/or cooling element.

The light generating device may be part of or may be applied in e.g. office lighting systems, household application systems, shop lighting systems, home lighting systems, accent lighting systems, spot lighting systems, theater lighting systems, architectural lighting, fiber-optics application systems, projection systems, self- lit display systems, pixelated display systems, segmented display systems, warning sign systems, medical lighting application systems, indicator sign systems, decorative lighting systems, portable systems, automotive applications, green house lighting systems, horticulture lighting, or LCD backlighting, etc. The light generating device may also be part of or may be applied in e.g. material curing systems, additive manufacturing systems, metrology systems, UV

sterilization system, (IR) imaging systems, fiber illumination systems, etc. In an aspect, the invention also provides a projection system or a luminaire comprising the light generating device as described herein, or a plurality of such light generating devices.

In yet a further aspect, the invention provides a projector comprising the light generating device as defined herein. As indicated above, of course the light projector may also include a plurality of such light generating devices.

In yet a further aspect, the invention also provides a lighting system configured to provide lighting system light, the lighting system comprising one or more light generating devices as defined herein. Here, the term“lighting system” may also be used for a (digital) projector. Further, the light generating device may be used for e.g. stage lighting (see further also below), or architectural lighting. Therefore, in embodiments the invention also provides a lighting system as defined herein, wherein the lighting system comprises a digital projector, a stage lighting system or an architectural lighting system. The lighting system may comprise one or more light generating devices as defined herein and optionally one or more second light generating devices configured to provide second light generating device light, wherein the lighting system light comprises (a) one or more of (i) the converter radiation as defined herein, and optionally (b) second light generating device light. Hence, the invention also provides a lighting system configured to provide visible light, wherein the lighting system comprises at least one light generating device as defined herein. For instance, such lighting system may also comprise one or more (additional) optical elements, like one or more of optical filters, collimators, reflectors, wavelength converters, lens elements, etc. The lighting system may be, for example, a lighting system for use in an automotive application, like a headlight. Hence, the invention also provides an automotive lighting system configured to provide visible light, wherein the automotive lighting system comprises at least one light generating device as defined herein and/or a digital projector system comprising at least one light generating device as defined herein. Especially, the light generating device may be configured (in such applications) to provide red light. The automotive lighting system or digital projector system may also comprise a plurality of the light generating devices as described herein.

Instead of the term“lighting system” also the term“light generating device” may be used.

Alternatively, the light generating device may be designed to provide high intensity UV radiation, e.g. for 3D printing technologies or UV sterilization applications. Alternatively, the light generating device may be designed to provide a high intensity IR light beam, e.g., to project IR images for (military) training purposes.

The elongated light transmissive body, and optionally also the optical element, may comprise light transmissive host material (thus not taking into account the luminescent material, or more especially in embodiments a luminescent species such as trivalent cerium), especially light transparent material for one or more wavelengths in the visible, such as in the green and red, and in general also in the blue. Suitable host materials may comprise one or more materials selected from the group consisting of a transmissive organic material, such as selected from the group consisting of PE (polyethylene), PP (polypropylene), PEN

(polyethylene napthalate), PC (polycarbonate), polymethylacrylate (PMA),

polymethylmethacrylate (PMMA) (Plexiglas or Perspex), cellulose acetate butyrate (CAB), silicone, polyvinylchloride (PVC), polyethylene terephthalate (PET), including in an embodiment (PETG) (glycol modified polyethylene terephthalate), PDMS

(polydimethylsiloxane), and COC (cyclo olefin copolymer). Especially, the light transmissive material may comprise an aromatic polyester, or a copolymer thereof, such as e.g.

polycarbonate (PC), poly (methyl)methacrylate (P(M)MA), polyglycolide or polyglycolic acid (PGA), polylactic acid (PLA), polycapro lactone (PCL), polyethylene adipate (PEA), polyhydroxy alkanoate (PHA), polyhydroxy butyrate (PHB), poly(3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN); especially, the light transmissive material may comprise polyethylene terephthalate (PET). Hence, the light transmissive material is especially a polymeric light transmissive material. However, in another embodiment the light transmissive material may comprise an inorganic material. Especially, the inorganic light transmissive material may be selected from the group consisting of glasses, (fused) quartz, transmissive ceramic materials (such as garnets), and silicones. Glass ceramic materials may also be applied. Also hybrid materials, comprising both inorganic and organic parts may be applied. Especially, the light transmissive material comprises one or more of PMMA, COC (or COP) transparent PC, or glass.

As indicated above, these materials may also be selected for the beam shaping light transmissive body material(s).

When a luminescent material, like an inorganic luminescent material, quantum dots, organic molecules, etc., are embedded in a host matrix, the concentration of the luminescent material may in embodiments be selected from the range of 0.01-5 wt% (weight %), such as 0.01-2 wt%.

High brightness light sources may be used in e.g. front projectors, rear projectors, studio lighting, stage lighting, entertainment lighting, automotive front lighting, architectural lighting, augmented illumination (incl. data/content), microscopy, metrology, medical applications, e.g. digital pathology, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Figs la-le schematically depict some aspects of the invention; and Figs. 2a-2e schematically depict some embodiments; and

Figs. 3a-3d schematically depict some embodiments and simulation results. The schematic drawings are not necessarily on scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A light emitting device according to the invention may be used in applications including but not being limited to a lamp, a light module, a luminaire, a spot light, a flash light, a projector, a (digital) projection device, automotive lighting such as e.g. a headlight or a taillight of a motor vehicle, arena lighting, theater lighting and architectural lighting.

Light sources which are part of the embodiments according to the invention as set forth below, may be adapted for, in operation, emitting light with a first spectral distribution. This light is subsequently coupled into a light guide or waveguide; here the light transmissive body. The light guide or waveguide may convert the light of the first spectral distribution to another spectral distribution and guides the light to an exit surface.

An embodiment of the light generating device as defined herein is schematically depicted in Fig. la. Fig. la schematically depicts a light generating device 1 comprising a plurality of solid state light sources 10 and a luminescent concentrator 5 comprising an elongated light transmissive body 100 having a first face 141 and a second face 142 defining a length L of the elongated light transmissive body 100. The elongated light transmissive body 100 comprising one or more radiation input faces 111, here by way of example two oppositely arranged faces, indicated with references 143 and 144 (which define e.g. the width W), which are herein also indicated as edge faces or edge sides 147. Further the light transmissive body 100 comprises a radiation exit window 112, wherein the second face 142 comprises the radiation exit window 112. The entire second face 142 may be used or configured as radiation exit window. The plurality of solid state light sources 10 are configured to provide (blue) light source light 11 to the one or more radiation input faces 111. As indicated above, they especially are configured to provide to at least one of the radiation input faces 111 a blue power W_opt of in average at least 0.067 Watt/mm². Reference BA indicates a body axis, which will in cuboid embodiments be substantially parallel to the edge sides 147. Reference 140 refers to side faces or edge faces in general.

The elongated light transmissive body 100 may comprise a ceramic material 120 configured to wavelength convert at least part of the (blue) light source light 11 into converter light 101, such as at least one or more of green and red converter light 101. As indicated above the ceramic material 120 comprises an A BsOi2:Cc^’ ceramic material, wherein A comprises e.g. one or more of yttrium (Y), gadolinium (Gd) and lutetium (Lu), and wherein B comprises e.g. aluminum (Al). References 20 and 21 indicate an optical filter and a reflector, respectively. The former may reduce e.g. non-green light when green light is desired or may reduce non-red light when red light is desired. The latter may be used to reflect light back into the light transmissive body or waveguide, thereby improving the efficiency. Note that more reflectors than the schematically depicted reflector may be used. Note that the light transmissive body may also essentially consist of a single crystal, which may in embodiments also be A BsOi2:Cc^’ .

The light sources may in principle be any type of light source, but is in an embodiment a solid state light source such as a Light Emitting Diode (LED), a Laser Diode or Organic Light Emitting Diode (OLED), a plurality of LEDs or Laser Diodes or OLEDs or an array of LEDs or Laser Diodes or OLEDs, or a combination of any of these. The LED may in principle be an LED of any color, or a combination of these, but is in an embodiment a blue light source producing light source light in the UV and/or blue color-range which is defined as a wavelength range of between 380 nm and 490 nm. In another embodiment, the light source is an UV or violet light source, i.e. emitting in a wavelength range of below 420 nm. In case of a plurality or an array of LEDs or Laser Diodes or OLEDs, the LEDs or Laser Diodes or OLEDs may in principle be LEDs or Laser Diodes or OLEDs of two or more different colors, such as, but not limited to, UV, blue, green, yellow or red.

The light sources 10 are configured to provide light source light 11, which is used as pump radiation 7. The luminescent material 120 converts the light source light into luminescent material light 8 (see also Lig. le). Light escaping at the light exit window is indicated as converter light 101, and will include luminescent material light 8. Note that due to reabsorption part of the luminescent material light 8 within the luminescent concentrator 5 may be reabsorbed. Hence, the spectral distribution may be redshifted relative e.g. a low doped system and/or a powder of the same material. The light generating device 1 may be used as luminescent concentrator to pump another luminescent concentrator.

Ligs. la- lb schematically depict similar embodiments of the light generating device. Lurther, the light generating device may include further optical elements, either separate from the waveguide and/or integrated in the waveguide, like e.g. a light

concentrating element, such as a compound parabolic light concentrating element (CPC). The light generating devices 1 in Lig. lb further comprise a collimator 24, such as a CPC.

As shown in Pigs la- lb and other Pigures, the light guide has at least two ends, and extends in an axial direction between a first base surface (also indicated as first face 141) at one of the ends of the light guide and a second base surface (also indicated as second face 142) at another end of the light guide.

Pig. lc schematically depicts some embodiments of possible ceramic bodies or crystals as waveguides or luminescent concentrators. The faces are indicated with references 141-146. The first variant, a plate-like or beam-like light transmissive body has the faces 141-146. Light sources, which are not shown, may be arranged at one or more of the faces 143-146 (general indication of the edge faces is reference 147). This variant has a rectangular cross-section. The second variant is a tubular rod, with first and second faces 141 and 142, and a circumferential face 143. Light sources, not shown, may be arranged at one or more positions around the light transmissive body. Such light transmissive body will have a (substantially) circular or round cross-section. The third variant is substantially a combination of the two former variants, with two curved and two flat side faces.

In the context of the present application, a lateral surface of the light guide should be understood as the outer surface or face of the light guide along the extension thereof. For example in case the light guide would be in form of a cylinder, with the first base surface at one of the ends of the light guide being constituted by the bottom surface of the cylinder and the second base surface at the other end of the light guide being constituted by the top surface of the cylinder, the lateral surface is the side surface of the cylinder. Herein, a lateral surface is also indicated with the term edge faces or side 140.

The variants shown in Fig. lc are not limitative. More shapes are possible; i.e. for instance referred to W02006/054203, which is incorporated herein by reference. The ceramic bodies or crystals, which are used as light guides, generally may be rod shaped or bar shaped light guides comprising a height H, a width W, and a length L extending in mutually perpendicular directions and are in embodiments transparent, or transparent and luminescent. The light is guided generally in the length L direction. The height H is in embodiments < 10 mm, in other embodiments <5mm, in yet other embodiments < 2 mm. The width W is in embodiments < 10 mm, in other embodiments <5mm, in yet embodiments < 2 mm. The length L is in embodiments larger than the width W and the height H, in other embodiments at least 2 times the width W or 2 times the height H, in yet other embodiments at least 3 times the width W or 3 times the height H. Hence, the aspect ratio (of length/width) is especially larger than 1, such as equal to or larger than 2, such as at least 5, like even more especially in the range of 10-300, such as 10-100, like 10-60, like 10-20. Unless indicated otherwise, the term“aspect ratio” refers to the ratio length/width. Fig. lc schematically depicts an embodiment with four long side faces, of which e.g. two or four may be irradiated with light source light.

The aspect ratio of the height H : width W is typically 1 : 1 (for e.g. general light source applications) or 1 :2, 1 :3 or 1 :4 (for e.g. special light source applications such as headlamps) or 4:3, 16:10, 16:9 or 256:135 (for e.g. display applications). The light guides generally comprise a light input surface and a light exit surface which are not arranged in parallel planes, and in embodiments the light input surface is perpendicular to the light exit surface. In order to achieve a high brightness, concentrated, light output, the area of light exit surface may be smaller than the area of the light input surface. The light exit surface can have any shape, but is in an embodiment shaped as a square, rectangle, round, oval, triangle, pentagon, or hexagon. Note that in all embodiments schematically depicted herein, the radiation exit window is especially configured perpendicular to the radiation input face(s). Hence, in embodiments the radiation exit window and radiation input face(s) are configured

perpendicular. In yet other embodiments, the radiation exit window may be configured relative to one or more radiation input faces with an angle smaller or larger than 90°.

Note that, in particular for embodiments using a laser light source to provide light source light, the radiation exit window might be configured opposite to the radiation input face(s), while the mirror 21 may consist of a mirror having a hole to allow the laser light to pass the mirror while converted light has a high probability to reflect at mirror 21. Alternatively or additionally, a mirror may comprise a dichroic mirror.

Fig. ld very schematically depicts a projector or projector device 2 comprising the light generating device 1 as defined herein. By way of example, here the projector 2 comprises at least two light generating devices 1, wherein a first light generating device (la) is configured to provide e.g. green light 101 and wherein a second light generating device (lb) is configured to provide e.g. red light 101. Light source 10 is e.g. configured to provide blue light. These light sources may be used to provide the projection (light) 3. Note that the additional light source 10, configured to provide light source light 11, is not necessarily the same light source as used for pumping the luminescent concentrator(s). Further, here the term “light source” may also refer to a plurality of different light sources. The projector device 2 is an example of a lighting system 1000, which lighting system is especially configured to provide lighting system light 1001, which will especially include light generating device light 101.

High brightness light sources are interesting for various applications including spots, stage-lighting, headlamps and digital light projection.

For this purpose, it is possible to make use of so-called luminescent concentrators where shorter wavelength light is converted to longer wavelengths in a highly transparent luminescent material. A rod of such a transparent luminescent material can be used and then it is illuminated by LEDs to produce longer wavelengths within the rod.

Converted light which will stay in the luminescent material such as a doped garnet in the waveguide mode and can then be extracted from one of the surfaces leading to an intensity gain (Fig. le). Fig. le, but also other figures may also effectively schematically depict a luminaire 1100. The luminaire may further comprise one or more optics downstream of the device 1 (not depicted in Fig. le). Further, the luminaire may comprise a control system (not depicted) configured to control the light sources, or subsets of light sources. Fig. le also schematically depicts a light generating device 1 comprising a light source 10 configured to generate the light source light 11 as defined herein. Especially, Figs ld and le also schematically depict a projection system or a luminaire comprising the light generating device 1 as defined herein. The light generating device 100 is especially configured to generate light generating device light 101, which may comprise the luminesce cent material light 8, such as during a mode of operation of the light generating device.

High-brightness LED-based light source for beamer applications appear to be of relevance. For instance, the high brightness may be achieved by pumping a luminescent concentrator rod by a discrete set of external blue LEDs, whereupon the phosphor that is contained in the luminescent rod subsequently converts the blue photons into green or red photons. Due to the high refractive index of the luminescent rod host material (typically ~

1.8) the converted green or red photons are almost completely trapped inside the rod due to total internal reflection. At the exit facet of the rod the photons are extracted from the rod by means of some extraction optics, e.g. a compound parabolic concentrator (CPC), or a micro- refractive structure (micro-spheres or pyramidal structures). As a result the high luminescent power that is generated inside the rod can be extracted at a relatively small exit facet, giving rise to a high source brightness, enabling (1) smaller optical projection architectures and (2) lower cost of the various components because these can be made smaller (in particular the, relatively expensive, projection display panel).

Fig. 2a schematically depicts an embodiment of an arrangement 500 as described herein. The arrangement 500 comprises an elongated light transmissive body 100 and a beam shaping optical element 224.

The elongated light transmissive body 100 has a side face 140 and a radiation exit window 112, wherein the elongated light transmissive body 100 comprises a luminescent material 120 configured to convert at least part of light source light 11 into luminescent material light 8. For instance, the elongated light transmissive body 100 may e.g. be a garnet based rod with a rectangular cross-section (perpendicular to the plane of drawing), with the garnet being doped with cerium.

The beam shaping optical element 224 comprises a beam shaping light transmissive body 210 having a radiation entrance window 211 optically coupled with the first radiation exit window 112 and part of the side face 140 for receipt of at least part of the luminescent material light 8. The beam shaping light transmissive body 210 may e.g. be glass or silicone. At the external of the beam shaping light transmissive body 210, a specular reflector may be available. As shown, over a length dl, the beam shaping light transmissive body 210 is (also) adjacent to the side face 140. In this way, the beam shaping light transmissive body 210 optically coupled with the side face 140. The length dl may be less than 1% of the total length L of the elongated light transmissive body 100.

Fig. 2a also shows an embodiment of a light generating device 1 comprising an elongated light transmissive body 100, a light source 10, and a beam shaping optical element 224. The light source 10 is configured to provide light source light 11. The elongated light transmissive body 100 has a side face 140 and a radiation exit window 112, wherein the elongated light transmissive body 100 is configured to receive at least part of the light source light 11, wherein the elongated light transmissive body 100 comprises a luminescent material 120 configured to convert at least part of light source light 11 into luminescent material light 8. The beam shaping optical element 224 comprises a radiation entrance window 211 optically coupled with the first radiation exit window 112 and part of the side face 140 for receipt of at least part of the luminescent material light 8, wherein the beam shaping optical element 224 is configured to beam shape the received luminescent material light 8.

The elongated light transmissive body 100 has a first face 141 and the radiation exit window 112 defining a length L of the elongated light transmissive body 100, wherein the side face 140 comprises the radiation input face 111. The luminescent element 5 configured to couple at least part of the luminescent material light 8 out at the first radiation exit window 112 as converter light 101.

Figs. 2a-2c all show embodiments wherein the radiation entrance window 211 comprises an indentation 214 hosting part of the elongated light transmissive body 100, and wherein the indentation 214 has a depth, indicated with d2, selected from the range of 0.1-5 mm. The depth d2 of the indentation 214 may be about the same value as the length over which the beam shaping light transmissive body 210 protrudes over the elongated light transmissive body 100 to provide the optical coupling with the side face 140. For instance, dl<d2<dl*3, such as especially dl<d2<dl*2.

Figs. 2a-2c also show embodiments wherein the beam shaping light transmissive body 210 is a monolithic body comprising a beam shaping light transmissive body material, such as selected from the group of quarts, glass, ceramic and polymer. For instance, the polymer material comprises silicone, and wherein the beam shaping light transmissive body 210. In Fig. 2a, the beam shaping light transmissive body 210 may be an overmolded body, whereby physical contact with the side face and the radiation exit window may be obtained. Hence, in such embodiments the beam shaping light transmissive body 210 is in physical contact with both the first radiation exit window 112 and part of the side face 140.

Figs. 2b-2c schematically show embodiments wherein between one or more of the beam shaping light transmissive body 210 and the first radiation exit window 112, and the beam shaping light transmissive body 210 and the part of the side face 140, a light transmissive material 217 is configured, wherein the light transmissive material 217 is selected from an adhesive material and a frit material.

Fig. 2c schematically depicts an embodiment wherein the first radiation exit window 112 is non-planar. Further, though not necessary, the indentation 214 has a shape 215 corresponding to the non-planar first radiation exit window 112. For instance, the first radiation exit window 112 is one dimensionally curved, two dimensionally curved or facetted.

Fig. 2d schematically depicts an embodiment wherein beam shaping light transmissive body 210 is a composite body, comprising a first part 218 that is in physical contact with the part of the side face 140, and a second part 219 that is in optical contact with the first radiation exit window 112. For instance, the first part 218 may be selected from an adhesive material and a frit material, such as a silicone adhesive material. Such materials are light transmissive materials 217.

In embodiments, the beam shaping light transmissive body material of Figs. 2a-2c may comprise silicone. In a further embodiment, the second part 219 of the

embodiment of Fig. 2d that is in optical contact with the first radiation exit window 112, may be silicone. Note that between beam shaping light transmissive body material 210 and the radiation exit window 112 and the first radiation entrance window 211 there may also be a light transmissive material, like adhesive material. Here, in Fig. 2d an embodiment is schematically depicted wherein they are in physical contact.

In Fig. 2d, the beam shaping optical element comprises a radiation entrance window 211 configured to receive at least part of the luminescent material light. The radiation entrance window 211 has a radiation entrance window surface area which is larger than the first radiation exit window (212) surface area A2. In this embodiment, a truncated collimator has been applied, such as a truncated CPC. The radiation exit window 212 of the beam shaping optical element 224 has a surface area Al.

In Fig. 2d, the beam shaping light transmissive body 210, i.e. the second part 219, is in physical contact with the first radiation exit window 112, and the beam shaping light transmissive body 210, i.e. the first part 218, is in physical contact with part of the side face 140. The different parts 218,219 are indicated with different hatchings.

The beam shaping light transmissive body 210 is a solid body. Equal to or less than about 10 vol.% of the total volume of the beam shaping light transmissive body 210 may be occupied by the first part 218, of light transmissive material 217. Equal to 10 vol.% or more of the total volume of the beam shaping light transmissive body 210 may be occupied by the second part 219.

Fig. 2e schematically depicts an embodiment with a beam shaping optical element 224. The beam shaping light transmissive body 210, i.e. the second part 219, is in physical and optical contact with the first radiation exit window 112, and the beam shaping light transmissive body 210, i.e. the first part 218, is in further physical and optical contact with part of the side face 140. The different parts 218,219 are indicated with different hatchings. The light transmissive material 217 covers both a part of the side face 140 and a part of the side face of the beam shaping light transmissive body 210. The side face of the beam shaping light transmissive body 210 extends between the radiation entrance window 211 of the beam shaping optical element 224 and the radiation exit window 212 of the beam shaping optical element 224.

The rod-CPC interface may be a flat surface, and the mating faces of rod and CPC may be equal in size. With the CPC a lot of light is extracted from the small end face, the“nose” of the rod. Depending on the refractive indices of both rod and CPC a certain extraction efficiency is obtained. In an analytic approach this efficiency is the Native Ray Efficiency, which is thought to be the maximum obtainable efficiency of the rod-CPC combination for light extraction.

Assuming an elongated body having an index of refraction of about 1.84, although the CPC index of 1.84 has the best extraction performance with a rod of similar index of 1.84, (NRE=0.68) CPC material with a lower index of refraction, e.g. about n=l.52 index may be used in combination with the n=l .84 rod (NRE=0.58). Glue with a similar index as the CPC may be used as bonding material on the interface of rod and CPC.

A difference between the extraction by a CPC n=l .52 and a CPC n=l .84 relates to the so called Locked- in light fraction, the light generated by the phosphor which cannot escape an ideal rod with a low index CPC. This fraction is 25% of the light in case of n=l.52 CPC. Part of the 25% Locked-in light is re-oriented due to scattering or reabsorption and re-emission, and extracted after ah by the CPC, but another part of the Locked-in Light is lost due to side-extraction of the rod or it is lost by Excited State Absorption. The net gain of a high-n (n=l.84) CPC is around 18% as compared to a low-n (n=l.52) CPC if losses in the CPC are comparable for both CPCs. The high n CPC goes at a cost: the Etendue is increased a lot, from l6.5mm2.sr to 24.3mm2.sr for a n=l.84 rod with l.2mm x l.9mm cross section.

It surprisingly appears that a way to extract the Locked- in Light out of a rod with low n CPC is by using side-extraction of light close to the CPC and redirect the light to the CPC exit plane. The Locked in light has ray orientations under 56 - 90 degrees with the z- axis. This light reflects on the rod side walls typically every mm. If material of n»l, like n=l .52 is connected to the last mm of the rod, a large part of the Locked in Light is coupled out.

Hence, amongst others it is proposed to have the rod intruded over a small length into the CPC (intrusion < 2mm for 1.2 mm x 1.9 mm rod cross section of the rod). Lurther, it appears that even better results may be obtained when the rod front face (nose) is provided with facets, or with a single radius (spherical cap) or with 2 radii (ellipsoidal surface), in principle in a convex way for the rod and concave for the CPC.

Therefore, in an embodiment the CPC has overlap with the rod. This can be realized as in Ligs.2a-2e, especially with insertion of the rod in a cavity of a CPC, see Pigs. 2a-2c. Some tolerances are allowed as glue with similar or higher refractive index than the CPC can be used to fill the gaps. The glass part has very sharp edges. Instead of intrusion, a truncated CPC can be used, and the remainder of the outlined volume is filled with glue. Simulations of this configuration show a considerable increase of 18% of the total light output, and an increase of 3% of the light output within the Etendue of the original design with no overlap. Results are shown in Pig. 3a. On the x-axis, the immersion depth is indicated, which equals the length dl, the beam shaping light transmissive body 210 is (also) adjacent to the side face 140. On the y-axis, the radiation conversion efficiency h in % is indicated (values, see right y-axis) defined as outcoupled converted light in Watt divided by light of blue light source also in Watt; the maximum is about 0.39, see Rl.

References Rl, R2, R3 and R4 total output for a reference system without immersion. Rl refers to, as indicated above to a combination of a high refractive index elongated body and high refractive index beam shaping element, such as both about 1.8. Reference R2 refers to a similar system, but now with a low refractive index beam shaping element, such as having a refractive index of about 1.5, and for the total etendue. Reference R3 is identical to reference R2, except that an etendue of 16.5 sr*mm² is chosen (wherein sr indicates the solid angle). Reference R4 is again the same as R3, but now again a high refractive index elongated body and high refractive index beam shaping element is chosen, such as both about 1.8, but at an etendue of 16.5 sr*mm²; in other words R4 is identical to Rl, but now only an etendue of 16.5 sr*mm² is chosen, instead of all output. For all reference R1-R4 values applies that there was no overlap between the beam shaping light transmissive body and the side face, which is herein also indicated as“no immersion”, or similar indications. As indicated above, the (physical and/or optical) connection between a high refractive index elongated body and high refractive index beam shaping elements. For instance, there are no (good) optically transparent adhesives with a high index of refraction, such as about 1.8. or even (slightly) above.

The data indicated with reference V 1 refer to the values of the total extraction; reference V2 refer to the increase in intensity within the etendue, in a configuration with overlap between the beam shaping light transmissive body 210 and the side face. Hence, in this embodiment the immersion depths should be selected from the range of about 0.05-0.15 mm.

Fig. 3b schematically depicts an embodiment of the arrangement 500 wherein the radiation exit window 112 is two dimensionally curved; and the indentation 214 has a corresponding shape.

Hence, in a specific embodiment (see also above), the front side (nose) of the rod is no longer a flat, but double curved (as in Fig. 3b) or faceted, while the CPC has some overlap with the rod. The CPC can be truncated and glue can be used to fill the outline according to the original CPC shape. From simulations it is concluded that the double curved (spherical cap) surface of the interface results in a 4% increase of the performance within the etendue relative to a flat interface design. This improvement is realized without (yet) overlap of rod and CPC. With some overlap, at best an overlap of 0.12 mm, 5% improvement of the light output within etendue of the flat is achieved. The total light extraction is increased by 18%, this gain is mainly outside the original etendue.

Fig. 3c shows the simulation results of such embodiments, wherein Rl, R2,

R3, R4, VI and V2 are as defined above, but now for an embodiment wherein the radiation exit window 112 is two dimensionally curved.

A problem solved with the invention is the extraction of Locked-In Light from the sides of the rod. Moreover, an optical efficiency gain is achieved by deviations from a perpendicular flat of the rod-CPC interface, which also relates to extraction of Locked- in Light.

CPCs may e.g. be manufactured out of glass by glass molding. The interface to the rod mat either ready-molded or grinded/polished to a flat surface. After cleaning the CPC may be glued to the rod end facet with silicone glue, or alternatively, with glass CPCs of similar coefficient of thermal expansion (CTE) the CPC can be direct-bonded at elevated temperatures. The glued or direct-bonded flat interface may be very vulnerable for mechanical loads, shocks or vibrations.

With the present invention, extraction of Locked-In Light from the sides of the rod occurs. Further, assembly of rod and CPC including the alignment of the rod-CPC may be done in the overmolding process. The alignment of the mold parts is copied into the alignment of the rod and CPC. This can be done with an accuracy level that depends on the equipment, for silicone molding the conditions are the most favorable: low pressure and low temperature. Therefore, the CPC may hold onto the rod from five sides, by which the robustness of the connection is increased a lot (assuming the rod having a rectangular cross- section). The strength of the bond is also improved by the increased surface area. Both factors lead to an improved robustness of the product, more resistant to mechanical loads, shocks and vibrations and thus to increased lifetime of the product.

Further, the mass of the CPC may be reduced in case of silicone or polymer overmolds, which also leads to an improved robustness of the product, more resistant to mechanical loads, shocks and vibrations and thus to increased lifetime of the product.

A silicone CPC has a low stiffness which can absorb some displacement at the CPC flange which can enable dust-tight HLD modules and anti-crawling solutions which rely on mechanical touching of the CPC. Polymeric materials are also much less stiff than glass.

Further, silicone can have a very high transparency to have low optical losses and Fresnel reflections at the front surface. Yet further, the silicone CPC external surface can be very smooth to have a very low scatter level. A high surface quality is also possible with polymer injection molding.

Further, production of the arrangement of rod and CPC may be relatively easy, and the number of processing steps may be reduced.

In an example, a silicone CPC, with typically a refractive index of 1.41, or a polymer CPC, with polycarbonate as most promising material choice, or a glass CPC, is proposed.

In an example, a CPC is made by an overmolding process, for silicone via a low-pressure molding process, for a polymer CPC via injection molding, for glass CPC by glass pressing. In an example, a CPC with a small overlap with the long sides of the rod, the overlap being typically between 0.1 mm and 3 mm for a e.g. 1.2 mm x 1.9 mm rod cross section. The required overlap depends on the refractive index of the CPC.

As indicated above, the glued or bonded flat interface may be vulnerable for mechanical loads, shocks or vibrations. By the profiling of the interface the rod and CPC do not need active alignment systems but are self-aligning. This may simplify the assembly procedure. The accuracy of the alignment is improved and by that the optical performance improves.

Further, also the strength of the bond may be improved by the increased surface area, and in case of faceted structures mechanical loads on the interface bond are taken over by the rod and the CPC, which strengthens the connection. This leads to an improved robustness of the product, more resistant to mechanical loads, shocks and vibrations and thus to increased lifetime of the product.

Therefore, in embodiments a faceted interface of the rod or a spherical or ellipsoid shape of the interface is proposed. Additionally, a counter face of the CPC which has the inverse profile of the rod interface is proposed.

In embodiments, inclined contacting surfaces at the interface are proposed, leading to lateral movements when the parts are moved together.

In an embodiment for bonding of similar refractive index parts, these are the CPC, rod and optional interconnect materials like glue or frit glass. The shape of the rod end is faceted, for instance in a roof shape on top of the rod end face. The inclined sides can be adapted to have different inclinations from base to top. For instance, the inverse shape is in the CPC glass.

Manufacturing of the rod top can be done with 2D sawing or laser-cutting techniques, but the sharp edges are more difficult to remove. In the glass of the CPC the counter shape can be made with molding, but radii will be on all edges. The assembly of the parts may lead to risks if the rod shape has sharp edges and the CPC has rounded comers. In that case the sharp edges of the rod penetrate a bit into the rounded shapes of the CPC. This can cause stresses and fracture.

In an embodiment for bonding of similar refractive index parts, these are the CPC, rod and optional interconnect materials like glue or frit glass.

If z represents the rod axis, this interface leads to alignment in x and y, similarly as the‘roof or pyramid shape does. A profile on the rod including the required radii can be made by a cutting technology that only has lateral movements, like wire sawing, wire spark erosion, laser cutting, water-jet guided laser cutting. Rounding of edges is easy as an integral part of the 2D cutting process step. The structure on the CPC can be made by existing glass molding technology.

In an embodiment with different refractive index combinations of rod and CPC, the interface has only slight deviations from the flat interface. For instance, a spherical cap with a relatively large radius as compared to the rod width or height is proposed. Fig. 3d shows a shape that has small inclinations with respect to the flat, which is not sufficient for easy alignment in x and y (if z axis is the rod axis). But the spherical shape allows rotation about the z-axis of the rod with respect to the CPC. Upon applying rotation about z, possibly back and forth multiple times, the friction in x and y for self-alignment is reduced

significantly and in that case the angles are sufficient to achieve the alignment in x and y. The spherical cap on the rod could be made by special grinding technologies, the feasibility of which has not been investigated yet, while the concave shape in the CPC can be made by existing glass-molding technology.

The term“substantially” herein, such as in“substantially all light” or in “substantially consists”, will be understood by the person skilled in the art. The term “substantially” may also include embodiments with“entirely”,“completely”,“all”, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term“substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. Where stated that an absorption, a reflection or a transmission should be a certain value or within a range of certain values these values are valid for the intended range of wavelengths. Such, if stated that the transmission of an elongated luminescent light transmissive body is above 99%/cm, that value of 99%/cm is valid for the converted light rays within the desired range of wavelengths emitted by the light generating device 1 , while it would be clear to the person skilled in the art that the transmission of an elongated luminescent light transmissive body will be well below 99%/cm for the range of wavelengths emitted by the light sources 10, since the source light 11 is intended to excite the phosphor material in the elongated luminescent light transmissive bodies such that all the source light 11 preferably is absorbed by the elongated luminescent light transmissive bodies instead of highly transmitted.

The term“comprise” includes also embodiments wherein the term “comprises” means“consists of’. The term“and/or” especially relates to one or more of the items mentioned before and after“and/or”. For instance, a phrase“item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term "comprising" may in an embodiment refer to "consisting of' but may in another embodiment also refer to "containing at least the defined species and optionally one or more other species".

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words“comprise”,“comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to”. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Practical designs may be further optimized the person skilled in the art using optical ray trace programs, such particular angles and sizes of microstructures (reflective microstructures or refractive microstructures) may be optimized depending on particular dimensions, compositions and positioning of the one or more elongated light transmissive bodies.

The invention further applies to a device comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.

Claims

CLAIMS:

1. A light generating device (1) comprising a light source (10) configured to generate light source light (11) and an arrangement (500) of an elongated light transmissive body (100) and a beam shaping optical element (224), wherein:

the elongated light transmissive body (100) having a first face (141) and a second face (142) defining a length (L) of the light transmissive body (100), a side face (140) and a first radiation exit window (112), wherein the second face (142) comprises the first radiation exit window (112) and wherein the elongated light transmissive body (100) comprises a luminescent material (120) configured to convert at least part of the light source light (11) into luminescent material light (8);

- the beam shaping optical element (224) comprises a beam shaping light transmissive body (210) having a radiation entrance window (211) optically coupled with the first radiation exit window (112) and part of the side face (140) along the full circumference of the second face and for less than 5 % of the total area of the side face (140), for receipt of at least part of the luminescent material light (8),

the beam shaping optical element (224) is a compound parabolic concentrator.

2. The light generating device (1) according to claim 1, wherein the elongated light transmissive body (100) has a first index of refraction, and wherein the beam shaping light transmissive body (210) has a second index of refraction which is smaller than the first index of refraction.

3. The light generating device (l)according to any one of the preceding claims, wherein the hrst radiation entrance window (211) comprises an indentation (214) hosting part of the elongated light transmissive body (100), and wherein the indentation (214) has a depth selected from the range of 0.1 -5 mm.

4. The light generating device (1) according to any claim 3, wherein the first radiation exit window (112) is non-planar, and wherein the indentation (214) has a shape (215) corresponding to the non-planar first radiation exit window (112).

5. The light generating device (l)according to any one of the preceding claims, wherein the first radiation exit window (112) is one dimensionally curved, two dimensionally curved or facetted.

6. The light generating device (l)according to any one of the preceding claims, wherein the beam shaping light transmissive body (210) is in physical contact with one or more of the first radiation exit window (112) and part of the side face (140).

7. The light generating device (1) according to any one of the preceding claims 1-6, wherein the beam shaping light transmissive body (210) is a monolithic body comprising a beam shaping light transmissive body material is selected from the group of quarts, glass, ceramic and polymer.

8. The light generating device (l)according claim 7, wherein the beam shaping light transmissive body material comprises a polymer material, wherein the polymer material comprises silicone, and wherein the beam shaping light transmissive body (210) is an overmolded body.

9. The light generating device (l)according to any one of the preceding claims 1- 7, wherein between one or more of (i) the beam shaping light transmissive body (210) and the first radiation exit window (112), and (ii) the beam shaping light transmissive body (210) and the part of the side face (140), a light transmissive material (217) is configured, wherein the light transmissive material (217) is selected from an adhesive material and a frit material.

10. The light generating device (l)according to any one of the preceding claims 1- 6, wherein beam shaping light transmissive body (210) is a composite body, comprising a first part (218) that is in physical contact with the part of the side face (140), and a second part (219) that is in optical contact with the first radiation exit window (112), and wherein the first part (218) is selected from an adhesive material and a frit material.

11. The light generating device (1) according to claim 10, wherein the beam shaping light transmissive body material comprises silicone.

12. The light generating device (1) according to claim 6, wherein the beam shaping light transmissive body (210) is in physical contact with the first radiation exit window (112) with the surface area of the radiation entrance window (211) being substantial identical to the surface area of the first radiation exit window (112) and wherein a light transmissive material covers the part of the side face (140) as well as a part of a second side face of the beam shaping light transmissive body (210).

13. The light generating device (1) according to claim 12, wherein the light transmissive material is selected from and adhesive material and a frit material.

14. A projection system or a luminaire comprising the light generating device (1) according to claim 13.

15. A method for producing the light generating device (1) according to any one of the preceding claims 1-13, the method comprising providing the elongated light transmissive body (100) and providing the beam shaping optical element (224) by one of (i) overmolding the beam shaping optical element (224) to the elongated light transmissive body (100) and (ii) connecting the beam shaping optical element (224) and the elongated light transmissive body (100) with an adhesive material or a frit material, such that the radiation entrance window (211) is optically coupled with the first radiation exit window (112) and part of the side face (140).