WO2015028334A1

WO2015028334A1 - A light emitting device and a method for manufacturing a light emitting device

Info

Publication number: WO2015028334A1
Application number: PCT/EP2014/067567
Authority: WO
Inventors: Marc Andre De Samber; Norbertus Antonius Maria Sweegers
Original assignee: Koninklijke Philips N.V.
Priority date: 2013-08-29
Filing date: 2014-08-18
Publication date: 2015-03-05

Abstract

A light emitting device (1), and a method for manufacturing it are disclosed. The method comprises the steps of, in the order mentioned: providing at least one substrate (3) and at least one solid state light source (21, 22, 23), arranging the at least one solid state light source on the at least one substrate, providing a light guide (4) comprising a light input surface (41) and a light exit surface (42) extending in an angle different from zero to one another, shaping the light guide (4) to provide at least one cavity (91, 92, 93) in the light input surface (41) which is shaped such that it can accommodate the at least one solid state light source (21, 22, 23), mounting the at least one substrate with the at least one solid state light source arranged thereon onto the light guide and accommodating the at least one solid state light source (21, 22, 23) in the at least one cavity (91, 92, 93) such that the at least one solid state light source is at least partly embedded in the light guide to form a light emitting device body (501), and encapsulating the light emitting device body (501) partially in an envelope (85) such that the light emitting device body and the envelope are in physical contact to form a light emitting device (1) and such that the light exit surface of the light guide forms part of an outer surface of the light emitting device.

Description

A light emitting device and a method for manufacturing a light emitting device

FIELD OF THE INVENTION

The invention relates to a method for manufacturing a light emitting device. The invention further relates to a light emitting device manufactured by means of such a method.

BACKGROUND OF THE INVENTION

US 2011/0215355 Al describes a method for manufacturing a light emitting device including a solid state light source and a photonic crystal phosphor light conversion structure. The photonic crystal phosphor light conversion structure is in one embodiment arranged on a light emitting surface of the solid state light source. The photonic crystal phosphor light conversion structure may be attached to the light emitting surface of the solid state light source via an adhesive layer. Furthermore, the solid state light source and the photonic crystal phosphor light conversion structure may be mounted on a submount that provides external electrical connections and a protective cover or dome.

Todays' fabrication of light emitting devices is based on hybrid assembly onto a printed board, using an un-ideal mix of process steps and materials making the fabrication cumbersome and inefficient. Therefore a more industrialized and standardized manufacturing method is desired such as to obtain a reduction in complexity and an increased efficiency.

Also, e.g. for use in applications where a small form factor is required, a miniaturized build-up might be advantageous. This is also, and maybe even more important, the case for more complex build-ups, e.g. in which the light emitting device also includes an extra phosphor conversion element (e.g. a ceramic based phosphor platelet). Thus, there is also a need for a manufacturing method enabling suitable miniaturized build-ups to be achieved.

As it is desired to use such light emitting devices, particularly in the form of a light emitting device with a white light emitting source with top emission and with small (lateral) form factor, e.g. for automotive front lighting, there is furthermore a need for a manufacturing method enabling suitable product geometries to be achieved. JP2004241282A discloses a surface light emitting device provided with a LED chip and a light guide plate having a light extracting face and an end face. A part of the LED chip is embedded in the end face of the light guide plate, and the other part of the LED chip is exposed from the end face of the light guide plate. The LED chip is disposed so that its face exposed from the end face of the light guide plate is disposed on a mounting substrate. The mounting substrate is disposed on at least a part of the inner wall face of a casing. The surface light emitting device is formed by filling a light guide plate forming material to form the light guide plate in the casing disposed on at least a part of the inner wall face of the mounting substrate on which the LED chip is disposed.

US2008/232105A1 discloses a lighting module comprising one or more LED packages mounted on a circuit board; and an injection overmolding sealing the circuit board, the injection overmolding not having openings corresponding to piece holding pins, the injection overmolding not covering at least a light emitting portion of the one or more LED packages.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome at least some of these problems, and to provide a method for manufacturing a light emitting device which is simpler and more efficient, which is suitable for manufacturing miniaturized build-ups, and which allows for providing product geometries suitable for use in e.g. automotive lighting.

According to a first aspect of the invention, this and other objects are achieved by means of a method for manufacturing a light emitting device comprising the steps of, in the order mentioned:

providing at least one substrate,

providing at least one solid state light source comprising a light emitting surface,

arranging the at least one solid state light source on the at least one substrate such that the light emitting surface faces away from the substrate,

providing a light guide comprising a light input surface and a light exit surface extending in an angle different from zero to one another,

shaping the light guide to provide at least one cavity in the light input surface which is shaped such that it can accommodate the at least one solid state light source,

mounting the at least one substrate with the at least one solid state light source arranged thereon onto the light guide such that the light emitting surface faces the light guide and accommodating the at least one solid state light source in the at least one cavity such that the at least one solid state light source is at least partly embedded in the light guide, thereby forming a light emitting device body, and

encapsulating the light emitting device body in an envelope partially such that the light emitting device body and the envelope are in physical contact to form a light emitting device and such that the light exit surface of the light guide forms part of an outer surface of the light emitting device.

Thereby a method is provided which yields a 3-dimensionally shaped point light source, and with which both miniaturized build-ups and a wide variety of product geometries may be achieved as both the size and shape of the light emitting device may be chosen freely with a minimal effect on the method. Furthermore, the sequence in which the steps of the method are preformed provides for a method which may be performed as an in line manufacturing method and thus industrially in a very simple manner and which is efficient and timesaving.

In this connection the terms "shaping", "shaped" and the like are intended to encompass providing the light guide with any one or more of cavities, trenches, cut-outs, recesses or the like having a shape intended to match the shape of the solid state light sources and a pitch intended to match the pitch of the solid state light sources arranged on the substrate. Consequently the term "shape" is intended to encompass any one or more of cavities, trenches, cut-outs, recesses or the like provided in the light guide and having a shape intended to match the shape of the solid state light sources and a pitch intended to match the pitch of the solid state light sources arranged on the substrate. Likewise, the term

"embedded" is in this connection to be understood as placing the solid state light sources such as to be arranged each in such a cavity, trench, cut-out, recess or the like provided in the light guide.

Thereby a method is provided with which a light emitting device having a particularly efficient coupling of light from the light sources to the light guide may be manufactured, because a larger light in-coupling area is provided for. This in turn provides for a reduced loss of light and thus in turn to a light output of the light emitting device having a particularly high intensity.

In an embodiment the method comprises the steps of in the order mentioned: providing at least two substrates,

providing at least two solid state light sources each comprising a light emitting surface, arranging at least one of the at least two solid state light sources on each one of the at least two substrates such that the light emitting surface faces away from the substrate,

providing a light guide comprising two light input surfaces and a light exit surface, the light exit surface extending in an angle different from zero to both of the light input surfaces,

shaping the light guide to provide at least one cavity in the light input surfaces which is shaped such that it can accommodate the solid state light source,

mounting each of the at least two substrates each with at least one of the at least two solid state light sources arranged thereon onto a respective light input surface of the light guide such that the light emitting surface faces the light guide and accommodating at least one solid state light source in the at least one cavity such that the at least one solid state light source is at least partly embedded in the light guide, thereby forming a light emitting device body, and

encapsulating the light emitting device body partially in an envelope such that the light emitting device body and the envelope are in physical contact to form a light emitting device and such that the light exit surface of the light guide forms part of an outer surface of the light emitting device.

Thereby a method is provided which yields the above-mentioned advantages and which furthermore, due to the larger possible number of solid state light sources provided for, yields a light emitting device with a higher light input intensity and thus consequently a higher light output intensity.

In an embodiment the step of encapsulating comprises the steps of providing a mold, arranging the light emitting device body in the mold and molding the envelope around the light emitting device body.

Thereby a method is provided with which the envelope is provided

encapsulating the light emitting device body in a particularly simple manner. A further advantage is that the shape of the mold may be chosen according to the desired final shape of the light emitting device, thus providing an additional degree of freedom in the shaping of the light emitting device.

In an embodiment the method further comprises the step of providing the at least one substrate with a reflective layer.

Thereby a method is provided with which the resulting light emitting device is provided with an improved optical efficiency as the reflective layer has the effect of reflecting light from the light sources which may otherwise be lost because of light absorption by the substrate.

In an embodiment the method further comprises the steps of, prior to the step of arranging the at least one solid state light source on the at least one substrate, providing at least one electrical connection element and arranging the at least one electrical connection element on the at least one substrate such that one part of the electrical connection element forms an electrical connection with the at least one light source, and another part of the electrical connection element protrudes from the at least one substrate.

In an embodiment the step of encapsulating further comprises ensuring that part of the at least one electrical connection element extends out of or protrudes from the envelope such as to form an external contact element of the light emitting device.

By any of the above two embodiments a method is provided which ensures the electrical supply to the light sources of the light emitting device in a particularly simple, efficient and robust manner, and that an external electrical and mechanical connection is provided.

In an embodiment the method further comprises the steps of, prior to the step of encapsulating the light emitting body, providing a heat sink element and mounting the heat sink element onto the at least one substrate on a side of the at least one substrate opposite to the at least one light source.

Thereby a method is provided incorporating providing the light emitting device with a heat sink in a particularly simple manner. Providing the light emitting device with a heat sink has the advantage that the heat produced by the solid state light source may in an efficient manner be dissipated away from the light guide. This in turn provides for a raise in the maximum obtainable output light intensity of the light emitting device as well as for lowering or even eliminating the adverse effects on the optical performance of the light emitting device caused by excess heat in the light guide. Preferably, the heat sink is extending to the outer surface of the light emitting device, thereby allowing for an improved heat dissipation path. Alternatively, or in addition thereto, a physically attached and additional heat sink element may be added as well for even better heat management.

In an embodiment the method further comprises the steps of, prior to the step of encapsulating the light emitting body, providing at least one wavelength conversion element and mounting the at least one wavelength conversion element on a light exit surface of the light guide. Thereby a method is provided incorporating providing the light emitting device with a wavelength conversion element in a particularly simple manner. Providing the light emitting device with a wavelength conversion element has the advantage that a light emitting device is provided with which the color pattern of the light emitted by the light emitting device may be changed. Furthermore, a light emitting device is provided with which a particularly large amount of the converted light can be extracted from one of the surfaces, which in turn leads to a particularly high intensity gain.

In an embodiment at least two light sources are provided and the step of arranging the at least two light sources on the at least one substrate further comprises electrically interconnecting the at least two light sources.

Thereby a method is provided with which it becomes possible to provide two or more light sources with electricity from one common electrical supply in a particularly simple and efficient manner. Also, providing the light emitting device with more light sources provides for a light input and in consequence also a light output with a higher intensity.

In an embodiment the method further comprises the steps of providing at least one optical element and arranging the at least one optical element at a light exit surface of the light guide.

Thereby a method incorporating providing the light emitting device with an optical element in a particularly simple manner is provided. The high intensity image patterns and shapes, which may be obtained by means of the light emitting device, may be adjusted to a specific application or situation by providing the light emitting device with an optical element arranged at a light exit surface of the light guide. For instance the image pattern obtained may be filtered, such as filtered by color or polarization, focused, shaped or projected onto a surface. Suitable optical elements include, but are not limited to, refractive or diffractive elements, e.g. lenses, color filters, reflective elements, polarizers and pinholes as well as combinations of such elements.

In an embodiment the at least one solid state light source is adapted for, in operation, emitting blue light.

Light sources emitting blue light are particularly advantageous in combination with suitable light converting structures in light emitting devices to be manufactured for use in applications in which white light is desired. Preferably, each of the at least one solid state light sources of the light emitting device provided in the step of providing a light emitting device is a solid state light source, such as a Light Emitting Diode (LED) or a Laser or Organic Light Emitting Diode (OLED).

The invention further concerns a light emitting device comprising at least one substrate, at least one solid state light source comprising a light emitting surface, the at least one solid state light source being arranged on the at least one substrate such that the light emitting surface faces away from the substrate, a light guide comprising a light input surface and a light exit surface extending in an angle different from zero to one another, the light guide comprising at least one cavity in the light input surface which cavity is shaped such that it can accommodate the at least one solid state light source, the at least one substrate being mounted with the at least one solid state light source arranged in the at least one cavity of the light guide such that the at least one solid state light source is at least partly embedded in the light guide and such that the light emitting surface faces the light guide, thereby forming a light emitting device body, and an envelope encapsulating the light emitting device body partially such that the light emitting device body and the envelope are in physical contact to form a light emitting device and such that the light exit surface of the light guide forms part of an outer surface of the light emitting device.

In an embodiment the light guide comprises the light guide comprises a plurality of cavities in the light input surface and wherein each of a plurality of solid state light sources is accommodated in one of a plurality of cavities such the each of the plurality of solid state light sources is at least partly embedded in the light guide. In another embodiment the cavities are also provided in other surfaces of the light guide.

The invention also concerns an automotive lighting device and a projector comprising any one or more of a light emitting device according to the invention and a light emitting device manufactured by means of a method according to the invention.

It is noted that the invention relates to all possible combinations of features recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

Fig. 1 shows a 3-dimensional perspective view of a light emitting device comprising an exit phosphor. Figs. 2 shows a cross sectional view of a light emitting device comprising a phosphor wheel.

Fig. 3 shows side view of a light guide which is provided with an optical element at an exit surface.

Fig. 4 shows a side view of a lighting system with a light guide and additional light sources and which is provided with a filter and a dichroic optical element.

Figs. 5A-C show schematic side views of the components of a light emitting device according to the invention at three different stages in a first embodiment of a method for manufacturing a light emitting device according to the invention.

Fig. 5D shows a schematic side view of a finished light emitting device according to the invention manufactured by means of the first embodiment of a method according to the invention.

Fig. 6 shows a schematic side view of a light emitting device according to the invention manufactured by means of a second embodiment of a method according to the invention.

Fig. 7 shows a schematic side view of a light emitting device according to the invention manufactured by means of a third embodiment of a method according to the invention.

As illustrated in the figures, the sizes of layers, elements and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout, such that e.g. a light emitting device according to the invention is generally denoted 1, whereas different specific embodiments thereof are denoted by adding 01, 02, 03 and so forth to the general reference numeral. With regard to Figs. 1 to 4 showing a number of features and elements which may be added to any one of the embodiments of a light emitting device according to the invention, "00" has been added to all elements except those specific to one of these Figures.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

The following description will start with general considerations regarding applications, suitable light sources and suitable materials for various elements and features of a light emitting device according to the invention. For this purpose a number of features and elements which may be added to any one of the embodiments of a light emitting device according to the invention as set forth further below will be described with reference to Figs. 1 to 4. The specific embodiments of a light emitting device according to the invention will be described in detail with reference to Figs. 5 to 7.

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, are adapted for, in operation, emitting light with a first spectral distribution. This light is subsequently coupled into a light guide or waveguide. 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. The light source may in principle be any type of point 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 blue color-range which is defined as a wavelength range of between 380 nm and 495 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 source may be a red light source, i.e. emitting in a wavelength range of e.g. between 600 nm and 800 nm. Such a red light source may be e.g. a light source of any of the above mentioned types directly emitting red light or provided with a phosphor suitable for converting the light source light to red light. This embodiment is particularly

advantageous in combination with a light guide adapted for converting the light source light to infrared (IR) light, i.e. light with a wavelength of more than about 800 nm and in a suitable embodiment with a peak intensity in the range from 810 to 850 nm. In an embodiment such a light guide comprises an IR emitting phosphor. A light emitting device with these

characteristics is especially advantageous for use in night vision systems, but may also be used in any of the applications mentioned above.

Another example is combination of a first, red light source emitting light in a wavelength range between 480nm and 800 nm and coupling this light into a luminescent rod or waveguide, and a second light source, emitting blue or UV or violet light, i.e. with a wavelength smaller than 480 nm, and also coupling its emitted light into the luminescent waveguide or rod. The light of the second light source is converted by the luminescent waveguide or rod to a wavelength range between 480nm and 800nm, and the light of the first light source coupled into the luminescent waveguide or rod will not be converted. In other words, the second light source emits UV, violet or blue light and is subsequently converted by the luminescent concentrator into light in the green-yellow-orange-red spectral region. In another embodiment the first light source emits in a wavelength range between 500nm and 600nm, and the light of the second light source is converted by the luminescent waveguide or rod to a wavelength range between 500nm and 600nm. In another embodiment the first light source emits in a wavelength range between 600nm and 750nm, and the light of the second light source is converted by the luminescent waveguide or rod to a wavelength range between 600nm and 750nm. In an embodiment the light of the first light source is coupled into the luminescent waveguide or rod at another surface, for example a surface opposite to an exit surface of the light, than a surface where the light of the second light source is coupled into the luminescent waveguide or rod. These embodiments provide a luminescent waveguide or rod emitting in the red light range with an increased brightness.

The light guides as set forth below in embodiments according to the invention 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 preferably < 10 mm, more preferably <5mm, most preferably < 2 mm. The width W is preferably < 10 mm, more preferably <5mm, most preferably < 2 mm. The length L is preferably larger than the width W and the height H, more preferably at least

2 times the width W or 2 times the height H, most preferably at least 3 times the width W or

3 times the height H. 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.

Transparent light guides may in embodiments comprise a transparent substrate on which a plurality of light sources, for example LEDs, are grown epitaxially. The substrate is in embodiments a single crystal substrate, such as for example a sapphire substrate. The transparent growth substrate of the light sources is in these embodiments the light concentrating light guide.

The generally rod shaped or bar shaped light guide 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 light guides are cuboid, but 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.

The light guides may also be cylindrically shaped rods. In embodiments the cylindrically shaped rods have 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 guide. The flattened surface may also be used for placing heat sinks. The cylindrical light guide 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.

The light guides 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 guide is not a straight, linear bar or rod, but may comprise, for example, a rounded corner 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 guide 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 guide may be rigid while transparent parts of the light guide are flexible to provide for the shaping of the light guide along its length direction. The light sources may be placed anywhere along the length of the folded, bended and/or shaped light guide.

Suitable materials for the light guides as set forth below according to embodiments of the invention are sapphire, polycrystalline alumina and/or undoped transparent garnets such as YAG, LuAG having a refractive index of n = 1.7. An additional advantage of this material (above e.g. glass) is that it has a good thermal conductivity, thus diminishing local heating. Other suitable materials include, but are not limited to, glass, quartz and transparent polymers. In other embodiments the light guide material is lead glass. Lead glass is a variety of glass in which lead replaces the calcium content of a typical potash glass and in this way the refractive index can be increased. Ordinary glass has a refractive index of n = 1.5, while the addition of lead produces a refractive index ranging up to 1.7.

The light guides as set forth below according to embodiments of the invention may comprise a suitable luminescent material for converting the light to another spectral distribution. Suitable luminescent materials include inorganic phosphors, such as doped YAG, LuAG, organic phosphors, organic fluorescent dyes and quantum dots which are highly suitable for the purposes of embodiments of the present invention as set forth 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 phosphide (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 embodiments of the present invention as set forth below. However, it may be preferred for reasons of environmental safety and concern to use cadmium- free quantum dots or at least quantum dots having very low cadmium content.

Organic fluorescent dyes can be used as well. The molecular structure can be designed such that the spectral peak position can be tuned. Examples of suitable organic fluorescent dyes 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.

The luminescent material may also be an inorganic phosphor. Examples of inorganic phosphor materials include, but are not limited to, cerium (Ce) doped YAG

(Y3AI5O12) or LuAG (LU3A5O12). Ce doped YAG emits yellowish light, whereas Ce doped LuAG emits yellow-greenish light. Examples of other inorganic phosphors materials which emit red light may include, but are not limited to ECAS and BSSN; ECAS being Cai_ _xAlSiN₃:Eux wherein 0<x<l, preferably 0<x<0.2; and BSSN being Ba₂-_x-_zM_xSi₅-_yAlyN₈- yO_y:Eu_z wherein M represents Sr or Ca, 0<x<l, 0<y<4, and 0.0005<z<0.05, and preferably 0<x<0.2.

In embodiments of the invention as set forth below, the luminescent material is made of material selected from the group comprising (M(i__x__y) M<II>_x M<III>_y)₃

(M<IV>(i_z) Μ<ν>_ζ)5θΐ2 where M is selected from the group comprising Y, Lu or mixtures thereof, M<II> is selected from the group comprising Gd, La, Yb or mixtures thereof, M<III> is selected from the group comprising Tb, Pr, Ce, Er, Nd, Eu or mixtures thereof, M<IV> is Al, M<V> is selected from the group comprising Ga, Sc or mixtures thereof, and 0<x<l, 0<y<0.1, 0<z<l, (M₍i__x__y) M<II>_x M<III>_y)₂0₃ where M is selected from the group comprising Y, Lu or mixtures thereof, M<II > is selected from the group comprising Gd, La, Yb or mixtures thereof, M<III > is selected from the group comprising Tb, Pr, Ce, Er, Nd, Eu, Bi, Sb or mixtures thereof, and 0<x<l, 0<y<0.1, (M(i_ _x_y) M<II>_X M<III>y) S(i_z) Se where M is selected from the group comprising Ca, Sr, Mg, Ba or mixtures thereof, M<II> is selected from the group comprising Ce, Eu, Mn, Tb, Sm, Pr, Sb, Sn or mixtures thereof, M<III> is selected from the group comprising K, Na, Li, Rb, Zn or mixtures thereof, and 0<x<0.01, 0<y<0.05, 0<z<l, (M₍i__x__y) M<II>_x M<III>_y)0 where M is selected from the group comprising Ca, Sr, Mg, Ba or mixtures thereof, M<II> is selected from the group comprising Ce, Eu, Mn, Tb, Sm, Pr or mixtures thereof, M<III> is selected from the group comprising K, Na, Li, Rb, Zn or mixtures thereof, and 0<x<0.1, 0<y<0.1, (M(2-_X) M<II>_X M<III>₂)0₇ where M is selected from the group comprising La, Y, Gd, Lu, Ba, Sr or mixtures thereof, M<II> is selected from the group comprising Eu, Tb, Pr, Ce, Nd, Sm, Tm or mixtures thereof, M<III> is selected from the group comprising Hf, Zr, Ti, Ta, Nb or mixtures thereof, and 0<x<l, (M₍i__x) M<II>_x M<III>(i__y) M<IV>_y)0₃ where M is selected from the group comprising Ba, Sr, Ca, La, Y, Gd, Lu or mixtures thereof, M<II> is selected from the group comprising Eu, Tb, Pr, Ce, Nd, Sm, Tm or mixtures thereof, M<III> is selected from the group comprising Hf; Zr, Ti, Ta, Nb or mixtures thereof, and M<IV> is selected from the group comprising Al, Ga, Sc, Si or mixtures thereof, and 0<x<0.1, 0<y<0.1, or mixtures thereof.

Other suitable luminescent materials are Ce doped Yttrium aluminum garnet (YAG, Y₃AI₅O₁₂) and Lutetium- Aluminum-Garnet (LuAG). A luminescent light guide may comprise a central emission wavelength within a blue color-range or within a green color- range or within a red color-range. The blue color-range is defined between 380 nanometer and 495 nanometer, the green color-range is defined between 495 nanometer and 590 nanometer, and the red color-range is defined between 590 nanometer and 800 nanometer.

A selection of phosphors which may be used in embodiments is given in table 1 below along with the maximum emission wavelength.

Table 1

The light guides as set forth below according to embodiments of the invention may comprise regions with a different density of suitable luminescent material for converting the light to another spectral distribution. In an embodiment a transparent light guide comprises two parts adjacent to each other and only one of which comprises a luminescent material and the other part is transparent or has a relatively low concentration of luminescent material. In another embodiment the light guide comprises yet another, third part, adjacent to the second part, which comprises a different luminescent material or a different concentration of the same luminescent material. The different parts may be integrally formed thus forming one piece or one light guide. In an embodiment a partially reflecting element may be arranged between the different parts of the light guide, for example between the first part and the second part. The partially reflecting element is adapted for transmitting light with one specific wavelength or spectral distribution and for reflecting light with another, different, specific wavelength or spectral distribution. The partially reflecting element may thus be a dichroic element such as a dichroic mirror. In another embodiment (not shown) a plurality of wavelength converting regions of luminescent material is arranged at the light input surface of a transparent light guide above or on top of a plurality of light sources, such as LEDs. Thus the surface area of each of the plurality of wavelength converting regions correspond to the surface area of each of the plurality of light sources such that light from the light sources is coupled into the transparent light guide via the regions of luminescent material. The converted light is then coupled into the transparent part of the light guide and subsequently guided to the light exit surface of the light guide. The wavelength converting regions may be arranged on the light input surface or they may be formed in the light guide. The wavelength converting regions may form part of a homogeneous layer arranged on or in the light guide at the light input surface. Parts of the homogeneous layer extending between two neighboring wavelength converting regions may be transparent and may additionally or alternatively have the same refractive index as the wavelength converting regions. The different wavelength converting regions may comprise mutually different luminescent materials. The distance between the light sources and the luminescent regions may be below 2 mm, below 1 mm or below 0.5 mm.

In embodiments of the light emitting device according to the invention as set forth below a coupling structure or a coupling medium may be provided for efficiently coupling the light emitted by the light source into the light guide. The coupling structure may be a refractive structure having features, such as e.g. protrusions and recesses forming a wave shaped structure. The typical size of the features of the coupling structure is 5 μιη to 500 μιη. The shape of the features may be e.g. hemispherical (lenses), prismatic, sinusoidal or random (e.g. sand-blasted). By choosing the appropriate shape, the amount of light coupled into the light guide can be tuned. The refractive structures may be made by mechanical means such as by chiseling, sand blasting or the like. Alternatively, the refractive structures may be made by replication in an appropriate material, such as e.g. polymer or sol-gel material. Alternatively, the coupling structure may be a diffractive structure, where the typical size of the features of the diffractive coupling structure is 0.2 μιη to 2 μιη. The diffraction angles 9i_n inside the light guide are given by the grating equation λ/Λ = ¾, 'sinG_m - n_out 'sinBout, where λ is the wavelength of LED light, Λ is the grating period, ¾, and n_out are the refractive indices inside and outside the light guide, 9i_n and 9_0Ut are the diffraction angle inside and the incident angle outside the light guide, respectively. If we assume the same refractive index n_out =1 for low- index layer and coupling medium, we find, with the condition for total internal reflection ¾_η sinBi_n = n_out, the following condition: λ/Λ = 1 - sin9_0Ut, i.e. Λ = λ for normal incidence 9_0Ut = 0. Generally, not all other angles 9_0Ut are diffracted into the light guide. This will happen only if its refractive index ¾_η is high enough. From the grating equation it follows that for the condition ¾_η > 2 all angles are diffracted if Λ = λ. Also other periods and refractive indices may be used, leading to less light that is diffracted into the light guide. Furthermore, in general a lot of light is transmitted (0^th order). The amount of diffracted light depends on the shape and height of the grating structures. By choosing the appropriate parameters, the amount of light coupled into the light guide can be tuned. Such diffractive structures most easily are made by replication from structures that have been made by e.g. e-beam

lithography or holography. The replication may be done by a method like soft nano-imprint lithography. The coupling medium may e.g. be air or another suitable material.

Turning now to Fig. 1, a 3-dimensional perspective view of a light emitting device 1000 is shown comprising a light guide 4000 adapted for converting incoming light with a first spectral distribution to light with a second, different spectral distribution. The light guide 4000 shown in Fig. 1 comprises or is constructed as a wavelength converter structure 6000 having a first conversion part 6110 in the form of a UV to blue wavelength converter and a second conversion part 6120 in the form of a phosphor adapted to emit white light 1400 based on the blue light input from the first conversion part 6110. Hence, the light emitting device 1000 shown in Fig. 1 comprises a light source in the form of a plurality of LEDs 2100, 2200, 2300 emitting light in the UV to blue wavelength range. The LEDs 2100, 2200, 2300 are arranged on a base or substrate 1500. Particularly, the first conversion part 6110 comprises a polycrystalline cubic Yttrium Aluminum Garnet (YAG), doped with rare earth ions, in an embodiment Europium and/or Terbium, while the second conversion part 6120 comprises a yellow phosphor. This embodiment is advantageous in that the surface area of the light exit surface is smaller than the surface area required to build a light source consisting of direct light emitting LEDs. Thereby, a gain in etendue can be realized.

Alternatives for generating white light with a blue or UV light source include but are not limited to LEDs emitting blue light, which light is converted to green/blue light in the first conversion part 6110, which in turn is converted to white light by the second conversion part being provided as a red phosphor, and LEDs emitting blue light, which light is converted to green light in the first conversion part 6110, which in turn is mixed with red and blue light to generate a white LED source, wherein the mixing is achieved by means of a second conversion part in the form of a red phosphor in front of which a diffusor is arranged.

Fig. 2 shows a light emitting device 1001 comprising a light guide 4015 and adapted for converting incoming light with a first spectral distribution to light with a second, different from the first, spectral distribution. The light guide 4015 shown in Fig. 2 comprises or is constructed as a wavelength converter structure having a second conversion part 6120 provided in the form of a rotatable phosphor wheel 1600, and it further comprises a coupling element 7700 arranged between the first conversion part 6110 and the second conversion part 6120 or phosphor wheel 1600.

The light emitting device 1001 further comprises a light source in the form of a plurality of LEDs 2100, 2200, 2300 arranged on a base or substrate 1500. The plurality of LEDs 2100, 2200, 2300 are used to pump the first conversion part 6110, which is in the embodiment shown made of a transparent material, to produce light 1700 having a third spectral distribution, such as green or blue light. The phosphor wheel 1600, which is rotating in a rotation direction 1610 about an axis of rotation 1620, is used for converting the light 1700 having the third spectral distribution to light 1400 having a second spectral distribution, such as red and/or green light. It is noted that in principle any combination of colors of the light 1700 and the light 1400 is feasible.

As shown in Fig. 2, illustrating the phosphor wheel 1600 in a cross sectional side view, the phosphor wheel 1600 is used in the transparent mode, i.e. incident light 1700 enters the phosphor wheel 1600 at one side, is transmitted through the phosphor wheel 1600 and emitted from an opposite side thereof forming the light exit surface 4200. Alternatively, the phosphor wheel 1600 may be used in the reflective mode (not shown) such that light is emitted from the same surface as the surface through which it enters the phosphor wheel.

The phosphor wheel 1600 may comprise only one phosphor throughout.

Alternatively, the phosphor wheel 1600 may also comprise segments without any phosphor such that also part of the light 1700 may be transmitted without being converted. In this way sequentially other colors can be generated. In another alternative, the phosphor wheel 1600 may also comprise multiple phosphor segments, e.g. segments of phosphors emitting yellow, green and red light, respectively, such as to create a multi-colored light output. In yet another alternative, the light emitting device 1001 may be adapted for generating white light by employing a pixelated phosphor-reflector pattern on the phosphor wheel 1600.

In an embodiment the coupling element 7700 is an optical element suitable for collimating the light 1700 incident on the phosphor wheel 1600, but it may also be a coupling medium or a coupling structure such as e.g. the coupling medium or the coupling structure 7700 described above. The light emitting device 1001 may furthermore comprise additional lenses and/or collimators. For example, additional optics may be positioned such as to collimate the light emitted by the light sources 2100, 2200, 2300 and/or the light 1400 emitted by the light emitting device 1001.

Fig. 3 shows a light guide 4020 which comprises an optical element 8010 arranged with a light input facet 8060 in optical connection with a light exit surface 4200 of the light guide 4020. The optical element 8010 is made of a material having a high refractive index, in an embodiment a refractive index which is equal to or higher than that of the light guide 4020, and comprises a quadrangular cross section and two tapered sides 8030 and 8040. The tapered sides 8030 and 8040 are inclined outwardly from the light exit surface 4200 of the light guide 4020 such that the light exit facet 8050 of the optical element 8010 has a larger surface area than both the light input facet 8060 and the light exit surface 4200 of the light guide 4020. The optical element 8010 may alternatively have more than two, particularly four, tapered sides. In an alternative, the optical element 8010 has a circular cross section and one circumferential tapered side. With such an arrangement light will be reflected at the inclined sides 8030 and 8040 and has a large chance to escape if it hits the light exit facet 8050, as the light exit facet 8050 is large compared to the light input facet 8060. The shape of the sides 8030 and 8040 may also be curved and chosen such that all light escapes through the light exit facet 8050.

The optical element may also be integrally formed from the light guide 4020, for example by shaping a part of the light guide such that a predetermined optical element is formed at one of the ends of the light guide. The optical element may for example have the shape of a collimator, or may have a cross-sectional shape of a trapezoid and in an embodiment outside surfaces of the trapezoid shape are provided with reflective layers. Thereby the received light may be shaped such as to comprise a larger spot size while simultaneously minimizing the loss of light through other surfaces than the light exit surface, thus also improving the intensity of the emitted light. In another embodiment the optical element has the shape of a lens array, for example convex or concave lenses or combinations thereof. Thereby the received light may be shaped such as to form focused light, defocused light or a combination thereof. In case of an array of lenses it is furthermore feasible that the emitted light may comprise two or more separate beams each formed by one or more lenses of the array. In more general terms, the light guide may thus have differently shaped parts with different sizes. Thereby a light guide is provided with which light may be shaped in that any one or more of the direction of emission of light from the light exit surface, the beam size and beam shape of the light emitted from the light exit surface may be tuned in a particularly simple manner, e.g. by altering the size and/or shape of the light exit surface. Thus, a part of the light guide functions as an optical element.

The optical element may also be a light concentrating element (not shown) arranged at the light exit surface of the light guide. The light concentrating element comprises a quadrangular cross section and two outwardly curved sides such that the light exit surface of the light concentrating element has a larger surface area than the light exit surface of the light guide. The light concentrating element may alternatively have more than two, particularly four, tapered sides. The light concentrating element may be a compound parabolic light concentrating element (CPC) having parabolic curved sides. In an alternative, the light concentrating element has a circular cross section and one circumferential tapered side. If, in an alternative, the refractive index of the light concentrating element is chosen to be lower than that of the light guide (but higher than that of air), still an appreciable amount of light can be extracted. This allows for a light concentrating element which is easy and cheap to manufacture compared to one made of a material with a high refractive index. For example, if the light guide has a refractive index of n = 1.8 and the light concentrating element has a refractive index of n = 1.5 (glass), a gain of a factor of 2 in light output may be achieved. For a light concentrating element with a refractive index of n = 1.8, the gain would be about 10 % more. Actually, not all light will be extracted since there will be Fresnel reflections at the interface between the optical element or the light concentrating element and the external medium, generally being air. These Fresnel reflections may be reduced by using an appropriate anti-reflection coating, i.e. a quarter-lambda dielectric stack or moth-eye structure. In case the light output as function of position over the light exit facet is inhomogeneous, the coverage with anti-reflection coating might be varied, e.g. by varying the thickness of the coating.

One of the interesting features of a CPC is that the etendue (= n² x area x solid angle, where n is the refractive index) of the light is conserved. The shape and size of the light input facet of the CPC can be adapted to those of the light exit surface of the light guide and/or vice versa. A large advantage of a CPC is that the incoming light distribution is transformed into a light distribution that fits optimally to the acceptable etendue of a given application. The shape of the light exit facet of the CPC may be e.g. rectangular or circular, depending on the desires. For example, for a digital projector there will be requirements to the size (height and width) of the beam, as well as for the divergence. The corresponding etendue will be conserved in a CPC. In this case it will be beneficial to use a CPC with rectangular light input and exit facets having the desired height/width ratio of the display panel used. For a spot light application, the requirements are less severe. The light exit facet of the CPC may be circular, but may also have another shape (e.g. rectangular) to illuminate a particularly shaped area or a desired pattern to project such pattern on screens, walls, buildings, infrastructures etc.. Although CPCs offer a lot of flexibility in design, their length can be rather large. In general, it is possible to design shorter optical elements with the same performance. To this end, the surface shape and/or the exit surface may be adapted, e.g. to have a more curved exit surface such as to concentrate the light. One additional advantage is that the CPC can be used to overcome possible aspect ratio mismatches when the size of the light guide is restrained by the dimensions of the LED and the size of the light exit facet is determined by the subsequent optical components. Furthermore, it is possible to place a mirror (not shown) partially covering the light exit facet of the CPC, e.g. using a mirror which has a 'hole' near or in its center. In this way the exit plane of the CPC is narrowed down, part of the light is being reflected back into the CPC and the light guide, and thus the exit etendue of the light would be reduced. This would, naturally, decrease the amount of light that is extracted from the CPC and light guide. However, if this mirror has a high reflectivity, like e.g. Alanod 4200AG, the light can be effectively injected back into the CPC and light guide, where it may be recycled by TIR. This will not change the angular distribution of the light, but it will alter the position at which the light will hit the CPC exit plane after recycling thus increasing the luminous flux. In this way, part of the light, that normally would be sacrificed in order to reduce the system etendue, can be re-gained and used to increase for example the homogeneity. This is of major importance if the system is used in a digital projection application. By choosing the mirror in the different ways, the same set of CPC and light guide can be used to address systems using different panel sizes and aspect ratio's, without having to sacrifice a large amount of light. In this way, one single system can be used for various digital projection applications.

By using any one of the above structures described with reference to Fig. 3, problems in connection with extracting light from the high- index light guide material to a low-index material like air, particularly related to the efficiency of the extraction, are solved.

Fig. 4 shows a side view of a lighting system, e.g. a digital projector, with a light guide 4070 which is adapted for converting incident light 1300 in such a way that the emitted light 1700 is in the yellow and/or orange wavelength range, i.e. roughly in the wavelength range of 560 nm to 600 nm. The light guide 4070 may e.g. be provided as a transparent garnet made of ceramic materials such as Ce-doped (Lu,Gd)3Al₅0i₂,

(Y,Gd)3Al₅0i₂ or (Y,Tb)3Al₅0i₂. With higher Ce-content and/or higher substitution levels of e.g. Gd and/or Tb in favor of Ce, the spectral distribution of the light emitted by the light guide can be shifted to higher wavelengths. In an embodiment, the light guide 4070 is fully transparent.

At the light exit surface 4200 an optical element 9090 is provided. The optical element 9090 comprises a filter 9091 for filtering the light 1700 emitted from the light guide 4070 such as to provide filtered light 1701, at least one further light source 9093, 9094 and an optical component 9092 adapted for combining the filtered light 1701 and the light from the at least one further light source 9093, 9094 such as to provide a common light output 1400. The filter 9091 may be an absorption filter or a refiective filter, which may be fixed or switchable. A switchable filter may e.g. be obtained by providing a reflective dichroic mirror, which may be low-pass, band-pass or high-pass according to the desired light output, and a switchable mirror and placing the switchable mirror upstream of the dichroic mirror seen in the light propagation direction. Furthermore, it is also feasible to combine two or more filters and/or mirrors to select a desired light output. The filter 9091 shown in Fig. 6 is a switchable filter enabling the transmission of unfiltered yellow and/or orange light or filtered light, particularly and in the embodiment shown filtered red light, according to the switching state of the filter 9091. The spectral distribution of the filtered light depends on the characteristics of the filter 9091 employed. The optical component 9092 as shown may be a cross dichroic prism also known as an X-cube or it may in an alternative be a suitable set of individual dichroic filters.

In the embodiment shown two further light sources 9093 and 9094 are provided, the further light source 9093 being a blue light source and the further light source 9094 being a green light source. Other colors and/or a higher number of further light sources may be feasible too. One or more of the further light sources may also be light guides according to embodiments of the invention as set forth below. A further option is to use the light filtered out by the filter 9091 as a further light source. The common light output 1400 is thus a combination of light 1701 emitted by the light guide 4070 and filtered by the filter 9091 and light emitted by the respective two further light sources 9093 and 9094. The common light output 1400 may advantageously be white light.

The solution shown in Fig. 4 is advantageous in that it is scalable, cost effective and easily adaptable according to the requirements for a given application of a light emitting device according to embodiments of the invention.

With reference to Fig. 5A the method according to the invention generally first comprises providing at least one substrate 301 and at least one solid state light source, in this embodiment three solid state light sources 21, 22, 23, and arranging the solid state light sources 21, 22, 23 on a surface 31 of the at least one substrate 301. The solid state light sources 21, 22, 23 each comprise a light emitting surface 210, 220, 230 and are arranged on the substrate 301 in such a way that the light emitting surface 210, 220, 230 faces away from the substrate 301.

As shown in Fig. 5A the substrate 301 comprises in this embodiment a reflective layer 83, and three solid state light sources 21, 22, 23 are provided and arranged on a surface 31 of the reflective layer 83 of the substrate 301. The reflective layer is provided both as a finishing layer on the substrate and to act, in the final light emitting device provided by means of the method according to the invention, as a layer reflecting light emitted from the light guide 4 (cf. Fig. 5B) through other surfaces than the designated light exit surface 42 such as to enhance the intensity of the light emitted by the light emitting device.

Furthermore, an electrical connection element 81 is provided and arranged at a surface 32 of the substrate extending opposite to and parallel with the surface 31 on which the solid state light sources 21, 22, 23 are arranged, or in other words in the embodiment shown at the surface 32 extending opposite to and parallel with the reflective layer 83. A part 87 of the electrical connection element 81 is arranged such as to extend protruding from the substrate 3.

The electrical connection element 81 serves to ensure the connection to an external electrical supply for supplying the solid state light sources with electrical energy. A part 86 of the electrical connection element 81 serves to provide the electrical contact between the protruding part 87 of the electrical connection element 81 and at least the first solid state light source 23 of the three the solid state light sources 21, 22, 23. The parts 86, 87 may be forming an integral electrical connection element 81 , or may be provided as separate components being assembled in a method step.

The reflective layer 83 may be made of an electrically conductive material such as to serve as an element electrically interconnecting the three solid state light sources 21, 22, 23. In this embodiment the part 86 of the electrical connection element 81 is a through hole or via in the reflective layer 83 and connects the protruding part 87 of the electrical connection element 81 and the reflective layer 83. Alternatively a separate contact element electrically interconnecting the three solid state light sources 21, 22, 23 may be provided. In an alternative, the reflective layer 83 may simply be provided as a reflective film or coating.

The step of arranging the solid state light sources 21, 22, 23 on a surface 31 of the substrate 301 is in practice performed according to any suitable method for assembling a circuit board. Preferably, the solid state light sources may be manufactured separately and then arranged on, such as attached to, the substrate.

Furthermore, it is ensured that an optimal type of substrate according to application is provided, examples being e.g. a substrate made of a ceramic or MCPCB/IMS for thermal performance, with highly reflective finish layer for optical efficiency.

Alternatives include, but are not limited to, transparent materials as those described above, metals and combinations of the materials mentioned.

The solid state light sources are preferably LEDs, suitable types of LEDs being described above. In a particularly preferred embodiment the LEDs can be e.g. CSP- type parts, such LEDs being particularly suitable for use in a method according to the invention.

Next, with reference to Fig. 5B, the method according to the invention further generally comprises providing a light guide 4.

The light guide 4 is shown in a side view, and is shaped generally as a bar or rod having a light input surface 41 and a light exit surface 42 extending perpendicular to one another such that the light exit surface 42 is an end surface of the light guide 4. The light guide 4 further comprises a further surface 46 extending parallel to and opposite the light exit surface 42, the further surface 46 thus likewise being an end surface of the light guide 4. The light guide 4 comprises three further side surfaces of which two are denoted 43 and 45, respectively, on Fig. 5B while the third further side surface which extends opposite and parallel to the surface 43 is not visible on Fig. 5B. The light guide 4 may also be plate shaped, e.g. as a square or rectangular plate.

The light input surface 41 and the light exit surface 42 generally extend in an angle different from zero with respect to each other. In the embodiments shown herein the light input surface 41 and the light exit surface 42 extend perpendicular to each other. Also, the light input surface 41 and the light exit surface 42 may have different sizes, preferably such that the light input surface 41 is larger than the light exit surface 42.

Alternative configurations of the light emitting device according to the invention in which the light exit surface 42 and the further surface 46 are mutually opposite side surfaces and the light input surface 41 is an end surface are also feasible.

The light guide 4 shown in Fig. 5B is a transparent light guide. Suitable transparent materials are described above. The light guide 4 may alternatively be made of a garnet, suitable garnets being described above. Furthermore, the light guide 4 may be luminescent, wavelength converting, light concentrating or a combination thereof, suitable materials and dopants being described above.

The light guide 4 is shaped or provided with shapes, in this embodiment cavities 91, 92, 93, 94, 95, 96, shaped into the material of the light guide 4, more precisely in the light input surface 41 and in the surface 45 extending opposite and parallel to the light input surface 41. The cavities 91, 92, 93, 94, 95, 96 are shaped such as to each accommodate a solid state light source 21, 22, 23, 24, 25, 26 - cf. Fig. 5C. Thus, and as shown further in Figs. 5C and 5D the light guide 4 shown in Fig. 5B is provided in an embodiment being shaped such as to enable the solid state light sources to be embedded in the light guide and thus enabling mounting two substrates each with at least one solid state light source, in the embodiment shown three solid state light sources, arranged thereon onto the light guide 4. Obviously, the light guide 4 may be provided in embodiments enabling the mounting of just one substrate or of three or four substrates and/or enabling the mounting of substrates with another number of solid state light sources than three, such as one, two or four, arranged thereon.

In any event each solid state light source 21, 22, 23, 24, 25, 26 is assigned a cavity 91, 92, 93, 94, 95, 96, respectively, and thus the shape, position/pitch and number of cavities provided in the light guide 4 is chosen to match the shape, position/pitch and number of solid state light sources 21, 22, 23, 24, 22, 26 arranged on the substrate 301.

The light guide 4 may in principle be provided using any suitable method for manufacturing a light guide. Preferably, the light guide 4 is provided in a stand-alone method for fabricating a light guide. Suitable methods include but are not limited to, methods employing compacting and sintering a suitable material into a desired shape and methods employing cutting, milling, extruding, molding or the like of a block of a suitable material to provide the desired shape.

Next, with reference to Fig. 5C, the method according to the invention further generally comprises mounting the at least one substrate 301 with the at least one solid state light source 21, 22, 23 arranged thereon onto the light guide 4 to form a light emitting device body 501. The at least one substrate 301 with the at least one solid state light source 21, 22, 23 arranged thereon is mounted onto the light guide 4 in such a way that the surface 31 on which the solid state light sources 21, 22, 23 are mounted faces the light guide 4, or in other words with the light emitting surfaces 210, 220, 230 of the solid state light sources 21, 22, 23 facing the light guide 4. The solid state light sources 21, 22, 23 are generally arranged at the light input surface 41 of the light guide 4 such as to emit light into the light guide 4. In the embodiment shown the solid state light sources 21, 22, 23 are arranged in the respective cavities 91, 92 and 93, respectively, such that they are embedded in the light guide 4.

The at least one substrate 301 with the at least one solid state light source 21,

22, 23 arranged thereon is preferably mounted onto the light guide 4 using an optical adhesive to optically and mechanically bond the substrate 201 and/or the solid state light sources 21, 22, 23 to the light guide 4. Thereby a method providing a light emitting device having a particularly robust and durable structure in a very simple and fast manner is provided.

Alternatively, in embodiments where the light guide 4 comprises cavities for the light sources, the at least one substrate 301 with the at least one solid state light source 21, 22, 23 arranged thereon may be mounted onto the light guide 4 using a frictional engagement or possibly even an interlocking engagement to hold the solid state light sources 21, 22, 23 in the cavities 91, 92, 93.

In the embodiment shown in Fig. 5C, two identical substrates, namely a first substrate 301 and a second substrate 302 with solid state light sources 21, 22, 23, 24, 25, 26 mounted thereon are provided. The solid state light sources 21, 22, 23, 24, 25, 26 are arranged with their respective light emitting surface 210, 220, 230, 240, 250, 260 facing the light guide 4. More particularly, the solid state light sources 21, 22, 23, 24, 25, 26 are arranged with their respective light emitting surface 210, 220, 230, 240, 250, 260 facing a bottom surface of a cavity 91, 92, 93, 94, 95, 96 of the light guide 4.

Each of the first and second substrate 301, 302 further comprises an electrical connection element 81 and 82, respectively, and a reflective layer 83 and 84, respectively. Each of the electrical connection elements 81, 82 comprises two parts 86, 87 and 88, 89, respectively, as described above. The first substrate 301 is mounted on the light guide 4 such that the solid state light sources 21, 22, 23 arranged on the first substrate 301 are arranged in each their assigned cavity 91, 92 and 93, respectively, such as to be embedded in the light guide 4. Analogously, the second substrate 302 is mounted on the light guide 4 such that the solid state light sources 24, 25, 26 arranged on the second substrate 302 are arranged in each their assigned cavity 94, 95 and 96, respectively, such as to be embedded in the light guide 4. In this embodiment the first and second substrates 301, 302 are mounted on opposite, parallel surfaces 41 and 45 of the light guide 4, these two parallel surfaces 41 and 45 thus forming the light input surfaces of the light guide. Alternatively, the first and second substrates 301, 302 may be mounted on another pair of opposite, parallel surfaces of the light guide 4. An example would be mounting the first and second substrates 301 and 302 on the surfaces 42 and 46, respectively, of the light guide 4 in which case any of the four surfaces of the light guide 4 extending perpendicular thereto may be acting as the light output surface.

Finally, with reference to Fig. 5D, the method according to the invention generally comprises encapsulating the light emitting device body 501 manufactured as described above partially in an envelope 85 such that the light emitting device body 501 and the envelope 85 are in physical contact to form a light emitting device 1. Fig. 5D more particularly shows a schematic illustration of a finished light emitting device 1 according to the invention manufactured by means an embodiment of a method according to the invention.

The envelope 85 is provided such that the light exit surface 42 of the light guide 4 forms a part of the outer surface of the light emitting device 1.

Furthermore, the envelope 85 is preferably provided such that the parts 87, 88 of the electrical connection element 81, 82 extending protruding from the substrate 301, 302 extends (protrudes) at least partially out of the envelope 85.

The envelope 85 may in principle be provided using any suitable method. A preferred example is molding. Hence, the envelope 85 is preferably made by providing a mold, arranging the light emitting device body 501 in the mold and molding the envelope 85 around the light emitting device body 501 using a suitable material for the envelope 85.

Alternative methods for providing the envelope include, but are not limited to, potting and liquid filling.

The envelope 85 is preferably made of a highly reflective material, examples being described above.

Furthermore, the method according to the invention may comprise at least one post-processing step, e.g. to remove residues or flash layers resulting from the molding process, or to provide an outer finishing layer, coating or the like, such as e.g. a scattering layer or coating. Thereby a light emitting device is provided which is free of residues and flash layers resulting from the molding procedure. This in turn ensures a light emitting device which has both an aesthetically appealing finish and which is free of light losses, reflections and scattering effects which may otherwise occur due to the residues and flash layers. In alternative embodiments multiple, e.g. two, three or more, substrates with solid state light sources may be provided and mounted onto multiple, e.g. two, three or more, different surfaces of the light guide, and/or the light guide may be provided with other three dimensional shapes than rectangular, such as square or hexagonal. Thereby light emitting devices of other shapes than rectangular may be provided. In another alternative embodiment the light guide may be an angled light guide thus enabling angled positioning of the substrate(s) onto the light guide, such as to optimize the light emission efficiency.

Turning now to Fig. 6, a schematic side view of a light emitting device according to the invention manufactured by means of a second embodiment of a method according to the invention is shown.

This second embodiment of a method according to the invention differs from the method described in connection with Figs. 5A-D in that at least one heat sink element is provided such as to eventually be co-embedded into the envelope 85. In the embodiment shown a first heat sink element 701 and second heat sink element 702 are provided on each of the first and second substrate 301, 302, respectively. This results in a considerably improved thermal performance of the light emitting device 101.

The first and second heat sink elements 701, 702 are mounted onto the surface of the first and second substrates 301, 302 facing away from the solid state light sources 21, 22, 23, 24, 25, 26 in such a way as to make good thermal contact to the substrate and hence create an additional heat pathway for the dissipating of heat away from the light sources and thus, in the final light emitting device 101, away from the light guide. This step is performed prior to the step of encapsulating the light emitting device body 502 in the envelope 85.

The envelope 85 is preferably provided such that a surface of each heat sink element 701, 702 forms a part of the outer surface of the light emitting device 101.

Turning now to Fig. 7, a schematic side view of a light emitting device according to the invention manufactured by means of a third embodiment of a method according to the invention is shown.

This third embodiment of a method according to the invention differs from the method described in connection with Figs. 5A-D in that at least one optical element, in the embodiment shown a wavelength conversion element 401, is provided such as to eventually be co-embedded into the envelope 85.

The optical element is mounted onto the light exit surface 42 of the light guide 4 in such a way as to make good optical contact to the light guide 4 and hence create an additional or different color output from the final light emitting device 102. Preferably, the optical element is attached to the light guide 4 by means of an optical adhesive. This step is performed prior to the step of encapsulating the light emitting device body 503 in the envelope 85. By way of example, it may be of interest in view of some applications to provide an additional optical element in the form of a wavelength conversion element 401, such as e.g. a blue light to white light converter element.

The wavelength conversion element itself may be provided by means of methods such as molding and sintering, such methods being known per se.

Alternatively or in addition thereto, other types of optical elements may be provided, suitable optical elements and their function being described above.

The envelope 85 is preferably provided such that a surface of the optical element, as shown in Fig. 7 a surface of the wavelength conversion element 401, forms a part of the outer surface of the light emitting device 102.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

Particularly, the various elements and features of the various embodiments described herein may be combined freely.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

CLAIMS:

1. A method for manufacturing a light emitting device (1) comprising the steps of in the order mentioned:

providing at least one substrate (301),

providing at least one solid state light source (21, 22, 23) comprising a light emitting surface (210, 220, 230),

providing a light guide (4) comprising a light input surface (41) and a light exit surface (42) extending in an angle different from zero to one another,

shaping the light guide (4) to provide at least one cavity (91, 92, 93) in the light input surface (41) which is shaped such that it can accommodate the at least one solid state light source (21, 22, 23),

mounting the at least one substrate with the at least one solid state light source arranged thereon onto the light guide such that the light emitting surface faces the light guide, and accommodating the at least one solid state light source (21, 22, 23) in the at least one cavity (91, 92, 93) such that the at least one solid state light source is at least partly embedded in the light guide, thereby forming a light emitting device body (501), and

encapsulating the light emitting device body (501) partially in an envelope (85) such that the light emitting device body and the envelope are in physical contact to form a light emitting device (1) and such that the light exit surface of the light guide forms part of an outer surface of the light emitting device.

2. A method according to claim 1, comprising the steps of in the order mentioned:

providing at least two substrates (301, 302),

providing at least two solid state light sources (21, 22, 23, 24, 25, 26) each comprising a light emitting surface (210, 220, 230, 240, 250, 260),

arranging at least one of the at least two solid state light sources on each one of the at least two substrates such that the light emitting surface faces away from the substrate,

providing a light guide (4) comprising two light input surfaces (41, 45) and a light exit surface (42), the light exit surface extending in an angle different from zero to both of the light input surfaces,

shaping the light guide (4) to provide at least one cavity (91, 92, 93, 94, 95,

96) in the light input surfaces (41, 45) which is shaped such that it can accommodate the solid state light source (21, 22, 23, 24, 25, 26),

mounting each of the at least two substrates each with at least one of the at least two solid state light sources arranged thereon onto a respective light input surface of the light guide such that the light emitting surface faces the light guide and accommodating at least one solid state light source in the at least one cavity such that the at least one solid state light source is at least partly embedded in the light guide, thereby forming a light emitting device body (501), and

3. A method according to claim 1 or 2, wherein the step of encapsulating comprises the steps of providing a mold, arranging the light emitting device body (501) in the mold and molding the envelope (85) around the light emitting device body.

4. A method according to any one of the above claims and further comprising the step of providing the at least one substrate (301, 302) with a reflective layer (83, 84).

5. A method according to any one of the above claims and further comprising the steps of, prior to the step of arranging the at least one solid state light source on the at least one substrate, providing at least one electrical connection element (81 , 82) and arranging the at least one electrical connection element on the at least one substrate (301, 302) such that one part (86, 88) of the electrical connection element forms an electrical connection with the at least one light source, and another part (87, 89) of the electrical connection element extends protruding from the at least one substrate.

6. A method according to claim 5, wherein the step of encapsulating further comprises ensuring that part of the at least one electrical connection element (81 , 82) extends out of the envelope (85) such as to form an external contact element of the light emitting device.

7. A method according to any one of the above claims and further comprising the steps of, prior to the step of encapsulating the light emitting body, providing a heat sink element (701, 702) and mounting the heat sink element onto the at least one substrate (301, 302) on a side of the at least one substrate opposite to the at least one light source.

8. A method according to any one of the above claims and further comprising the steps of, prior to the step of encapsulating the light emitting body, providing at least one wavelength conversion element (401) and mounting the at least one wavelength conversion element (401) on a light exit surface (42) of the light guide (4).

9. A method according to any one of the above claims, wherein the step of mounting the at least one substrate comprises using a frictional engagement to hold the at least one solid state light source (21, 22, 23) in the at least one cavity (91, 92, 93).

10. A method according to any one of the above claims, wherein at least two light sources are provided and wherein the step of arranging the at least one solid state light source on the at least one substrate further comprises electrically interconnecting the at least two light sources.

11. A method according to any one of the above claims and further comprising the steps of providing at least one optical element and arranging the at least one optical element at a light exit surface (42) of the light guide (4).

12. A method according to any one of the above claims, wherein the at least one solid state light source is adapted for, in operation, emitting blue light.

13. A light emitting device comprising:

at least one substrate (301),

at least one solid state light source (21, 22, 23) comprising a light emitting surface (210, 220, 230), the at least one solid state light source being arranged on the at least one substrate such that the light emitting surface faces away from the substrate,

a light guide (4) comprising a light input surface (41) and a light exit surface (42) extending in an angle different from zero to one another, the light guide (4) comprising at least one cavity (91, 92, 93) in the light input surface (41) which cavity is shaped such that it can accommodate the at least one solid state light source (21, 22, 23),

the at least one substrate being mounted with the at least one solid state light source arranged in the at least one cavity (91, 92, 93) of the light guide (4) such that the at least one solid state light source is at least partly embedded in the light guide (4) and such that the light emitting surface faces the light guide, thereby forming a light emitting device body (501), and

an envelope (85) encapsulating the light emitting device body (501) partially such that the light emitting device body and the envelope are in physical contact to form a light emitting device (1) and such that the light exit surface of the light guide forms part of an outer surface of the light emitting device.

14. A light emitting device according to claim 13, wherein the light guide comprises a plurality of cavities in the light input surface (41) and wherein each of a plurality of solid state light sources is accommodated in one of a plurality of cavities such the each of the plurality of solid state light sources is at least partly embedded in the light guide (4).

15. An automotive lighting device or a projector comprising any one or more of a light emitting device according to claim 13 or 14 and a light emitting device manufactured by means of a method according to any one of claims 1-12.