WO2019228815A1

WO2019228815A1 - Light spreading from a led with a light guide

Info

Publication number: WO2019228815A1
Application number: PCT/EP2019/062494
Authority: WO
Inventors: Hugo Johan Cornelissen; Evgeni Arkadevich PATENT
Original assignee: Signify Holding B.V.
Priority date: 2018-05-31
Filing date: 2019-05-15
Publication date: 2019-12-05

Abstract

The invention provides a lighting system (1) comprising a light source (100), a light guide (200), and a light reflective element (300), wherein: - the light source (100) is configured to generate light source light (111), wherein the light source (100) comprises a light emitting surface (101) via which light source light (111) escapes from the light source (100); - the light guide (200) comprises a first face (201) and a second face (202) defining a light guide thickness (h1) with first light guiding material (205) in between the first face (201) and the second face (202); - the light reflective element (300) comprises a first element face (301) and a second element face (302) with second light guiding material (305) in between the first element face (301) and the second element face (302), and comprising a specular reflector (320) in optical contact with at least part of the second element face (302); - the light emitting surface (101) of the light source (100) is in optical contact with the first light guiding material (205); - the first element face (301) of the light reflective element (300) is in optical contact with part of the second face (202) of the light guide (200); - the light source (100), light guide (200), and light reflective element (300) are configured such that at least part of the light source light (111) is received by the specular reflector (320); and - the light reflective element (300) is configured such that at least 60% of the light source light (111) received by the specular reflector (320) is reflected back under total internal reflection angles (α) with the first face (201) of the light guide (200).

Description

Light spreading from a LED with a light guide

FIELD OF THE INVENTION

The invention relates to a lighting system as well as to a method for providing such lighting system. BACKGROUND OF THE INVENTION

Optics for lighting devices are known in the art. US2014/0268871, for instance, describes an optic for use with a light source in an illumination device, the optic comprising: a light guide made of light transmissive material, the light guide comprising:

a first surface; a second surface opposite the first surface; a light coupling area for receiving light from the light source; and a peripheral edge; a redirecting layer made of light transmissive material, the redirecting layer comprising a plurality of lenses in optical communication with the light guide for emitting light, the redirecting layer being optically attached to the first surface of the light guide; and a plurality of reflector elements optically connected to the second surface of the light guide, each reflector element being associated with a lens of the redirecting layer for ejecting light entering the reflector element from the light guide toward the associated lens.

SUMMARY OF THE INVENTION

Prior art lighting systems based on waveguides may still be relatively thick and/or include relatively bulky or complicated optics to provide the desired intensity distribution and/or beam shape of the light generated by such lighting system. Further, productions of such lighting systems may include alignment steps or specific precautions to facilitate alignment.

Hence, it is an aspect of the invention to provide an alternative lighting system, which preferably further at least partly obviates one or more of above-described drawbacks. Further, it is an aspect of the invention to provide an alternative method for providing such lighting system, which preferably further at least partly obviates one or more of above-described drawbacks, for instance by reducing the number of alignment steps or simplifying alignment. 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 lighting system (“system”) comprising a light source, a light guide (which may also be indicated as“waveguide”), and a semi-transparent light reflective element (“reflective element” or“reflective cup”), wherein:

the light source is configured to generate light source light, wherein the light source comprises a light emitting surface via which light source light escapes from the light source;

the light guide comprises (a first body with) a first face and a second face defining a light guide thickness (hl) with first light guiding material in between the first face and the second face;

the light reflective element comprises (a second body with) a first element face and a second element face with second light guiding material in between the first element face and the second element face, and comprising a specular reflector in optical contact with at least part of the second element face;

the light emitting surface of the light source is in optical contact with the first light guiding material;

the first element face of the light reflective element is in optical contact with part of the second face of the light guide;

the light source, light guide, and light reflective element are configured such that at least part of the light source light is received by the specular reflector; and

the light reflective element (and light guide) is (are) configured such that at least 40%, like especially at least 50%, even more especially at least 60%, such as at least 70, yet even more especially at least 80%, such as at least 90% of the light source light received by the specular reflector is reflected back under total internal reflection angles (a) with the first face of the light guide.

Such light system, or especially an arrangement of the light source, light guide, and reflective element, may relatively easily be assembled. Moreover, there is no need to adapt the light guide to couple the light of the light source efficiently in to the light guide. Further, alignment may be much easier then when the light guide is especially adapted to facilitate incoupling of light source light into the light guide. In this way, essentially any light guide plate may be used as light guide. Hence, flexibility in design is relatively large.

Further, the lighting system may be applied with light sources that generate white light. As indicated above, the invention provides a lighting system (and/or arrangement) which comprises a light source, a light guide, and a light reflective element.

The terms“light source” or“light reflective element” may refer a plurality of light sources or a plurality of light reflective elements, respectively. As will further be elucidated below, the term“light source” may refer to a plurality of light sources, such as a chip-on-board, which may in fact also be considered as single light source or a cluster of light sources. Especially, each light source or cluster of light sources is associated with a respective light reflective element, in embodiments where a plurality of (clusters of) light sources and a plurality of light reflective elements is available.

Hence, in specific embodiments, the system includes a single light source or single cluster of light sources and a single light reflective element. In yet other embodiments, the system comprises a plurality of (clusters of) light sources and a plurality of light reflective elements, respectively. In the latter embodiments, especially the (clusters of) light sources and associated light reflective element may be configured in a symmetrical arrangement.

The term“light source” may refer to a semiconductor light-emitting device, such as a light emitting diode (LEDs), a resonant cavity light emitting diode (RCLED), a vertical cavity laser diode (VCSELs), an edge emitting laser, etc.. The term“light source” may also refer to an organic light-emitting diode, such as a passive-matrix (PMOLED) or an active-matrix (AMOLED). In a specific embodiment, the light source comprises a solid state light source (such as a LED or laser diode). In an embodiment, the light source comprises a LED (light emitting diode). The term LED may also refer to a plurality of LEDs. 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. 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 term“light source” may also relate to a plurality of light sources, such as 2-2000 solid state light sources.

As indicated above, the light source of the lighting system may be configured to generate white light. The system may allow a distribution of the light source light over the waveguide, even though the light source light may include different wavelengths, which may be selected from the range of especially 380-780 nm. The term white light herein, is known to the person skilled in the art. It especially relates to light having a correlated color temperature (CCT) between about 2000 and 20000 K, especially 2700-20000 K, for general lighting especially in the range of about 2700 K and 6500 K, and for backlighting purposes especially in the range of about 7000 K and 20000 K, and especially within about 15 SDCM (standard deviation of color matching) from the BBL (black body locus), especially within about 10 SDCM from the BBL, even more especially within about 5 SDCM from the BBL. Hence, in embodiments the light source may comprise a chip-on-board light source, wherein the light source is configured to generate white light source light.

However, the system may also be configured to generate colored light. In yet further embodiments, the lighting system may comprise different subsets of each one or more light sources which are independently controllable, by which the spectral distribution of the light escaping from the lighting system (or arrangement) may be controlled. To this end, the lighting system may further comprise a control system.

As indicated above, the light source is configured to generate light source light, wherein the light source comprises a light emitting surface via which light source light escapes from the light source. When a light source comprises a plurality of light sources, i.e. cluster of light sources, functionally coupled to a single light reflective element, such as when the light source comprises a COB, the light source comprises a plurality of adjacently arranged light emitting surfaces. In general, a total light emitting surface area, defined by the outer light sources in such cluster of light sources, may be at maximum 16 cm², such as at maximum 4 cm², such as in the range of 1-100 mm². In first approximation, the light source may be considered a point light source.

Further, the light guide comprises (a first body with) a first face and a second face defining a light guide thickness (hl) with first light guiding material in between the first face and the second face. In general, the light guide material is a solid material, though in specific embodiments it may be a gas or liquid contained in a container. Herein, the light guide is further described as comprising solid light guide material, i.e. the light guide material is solid.

The light guide is especially a body with a high light transmission. Hence, in embodiments the transmission for visible light is at least 80%/mm, even more especially at least 80%/5 mm, such as at least about 80%/l0 mm. The term“transmission” especially refers to internal transmission. The terms“internal transmittance” or“internal transmission”, or similar terms, refer to energy loss by absorption, whereas the terms“total transmittance” or“transmittance” or similar terms refer to transmission taking into account absorption, scattering, reflection, etc.. The transmission may be relatively large; even the total transmittance through a 5 mm thick layer of the material, under perpendicular irradiation with the (above-indicated) visible light may be at least about 80%, such as at least about 85%, like at least about 90%. In specific embodiments, the internal transmission for visible light is at least 80%/cm.

The light guide thus especially comprises light transmissive first light guiding material. The light transmissive material 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, and silicones. Also hybrid materials, comprising both inorganic and organic parts may be applied. Especially, the light transmissive material comprises one or more of PMMA, transparent PC, or glass.

The light guide may have any shape, but will especially have a height that is smaller than the length or width. Aspect ratios of height and length or height and width may in embodiments (each individually) be <1, such as <0.1. The light guide may be a plate-like shape, wherein a plane (or“plate plane”) through the plate has a circular, oval, triangular, square or rectangular cross-section. Other cross-sections may also be possible. When e.g. the plate has a circular or oval cross-section, the plate may have a 1D curvature, and be essentially flat. However, the plate may also have a 1D curvature perpendicular to the plane, such as when the plate has the shape of a (hollow) cylinder or part thereof. In embodiments, the plate may also have a 2D curvature perpendicular to the plane, such as when the plate has the shape of a (hollow) sphere or a part thereof, like a dome shape. Especially, however in embodiments the light guide is an essentially flat light guide with parallel faces, having a constant thickness, with an edge that is in embodiments essentially non-curved, such as in the case of a square or rectangular flat plate, or with an edge that is in embodiments curved, such as in the case of a circular flat plate, like a disc. Therefore, in specific embodiments the light guide may be planar and rotational symmetric relative to a rotational axis (A) configured perpendicular to the second face.

Yet further, the light reflective element comprises (a second body with) a first element face and a second element face with second light guiding material in between the first element face and the second element face, and comprising a specular reflector in optical contact with at least part of the second element face.

The first element face may have a flat or a curved shape. For instance, when the light guide is flat, the first element face will in general also be flat. When the light guide has a curved second face (i.e. the face is curved in a direction perpendicular to the face), the first element face may also be curved. However, in such embodiments the first element face may also be flat, as the first element face is in general much smaller than the second face of the light guide. For instance, a ratio of the equivalent diameter (or“equivalent circular diameter”) of the first element face to the equivalent diameter of the second face of the light guide may be equal to or smaller than 0.1. The equivalent circular diameter (or ECD) of an irregularly shaped two-dimensional shape is the diameter of a circle of equivalent area. For instance, the equivalent circular diameter of a square with side a is 2*a*SQRT( l/p). Even when a plurality of light sources and a plurality of light reflective elements is applied, a ratio of the sum of the equivalent diameters of the first element faces to the equivalent diameter of the second face of the light guide may be equal to or smaller than 0.5, such as equal to or smaller than 0.2, like equal to or smaller than 0.1.

In general, the first element has a circular cross-section but it may also be another regular shape like triangular, square, hexagonal or octagonal, etc.

The second element face is especially not parallel to the first face of the element. The light reflective element may e.g. have the shape similar to a (massive) dome or have the shape of a cone or have a combination of such shapes. Especially, the second element is two-dimensionally curved (see further also below). The light reflective element is especially a (small) massive body.

The light reflective element comprises a second lighting guiding material which may be selected from the group of light transmissive materials as defined above in relation to the first light guiding material. The first light guiding material and second light guiding material may be the same or may be different, see further also below.

The light reflective element further comprises a specular reflector in optical contact with at least part of the second element face. A specular reflector is an element that may provide a mirror-like reflection of the light source light that reaches (via the first light guiding material and second light guiding material) the specular reflector.

The specular reflector is in optical contact with at least part of the second element face. Optical contact may especially imply that the average distance between the specular reflector and the second element face 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 the part of the second element face and the specular reflector, such as a light transmissive adhesive. Especially, such intermediate light guiding material may have a refractive index, at e.g. 500 nm, which is essentially identical to the refractive index of the second light guiding material, or have a larger refractive index. For instance, a silicone glue may be used to arrange the specular reflector to the part of the second element face. In other embodiments, however, the specular reflector may over essentially its entire face be in physical contact with at least part of the second element face. The specular reflector may include a layer, such as a coating, of aluminum or silver.

In embodiments, the specular reflector is a continuous layer. In yet other embodiments, the specular reflector may include openings to allow transmission of at least part of the light that is received by one or more openings in the specular reflector.

In specific embodiments, essentially the entire second face of the light reflective element is optically coupled to the specular reflector. In yet other embodiments, 50-95%, such as 50-90%, of the area of the second faces is optically coupled to the specular reflector. The part of the second face of the light reflective element not optically coupled to the specular reflector may transmit at least part of the light source light receive by such part.

Hence, in embodiments the specular reflector is in optical contact with essentially the entire second element face. Hence, in such embodiments essentially no light may escape from the reflective element via the second element face, as light that escapes from the second element face, is reflected back into the reflective element (and subsequently in the light guide).

The first element face of the light reflective element may have a first equivalent diameter Dl and the light emitting surface of the light source may have a second equivalent diameter D2. Especially, a ratio of Dl/D2>l, such as Dl/D2>l.5.

The first element face of the light reflective element has a first equivalent diameter D 1 , the light emitting surface of the light source has a second equivalent diameter D2, wherein a critical angle is defined as Oc=arcsin(l/ni), wherein is the first refractive index of the first light guiding material, and wherein the first equivalent (Dl) complies with Dl=a*2*hl*tan(0c)+D2, wherein 0.9<a<l.l. In a preferred embodiment, especially

0.95<a<l.05, such as a is about 1.

The light emitting surface is not necessarily circular and/or the light reflective element has not necessarily a circular cross-section. Dependent upon the dimension, the above formulas can be adapted. Especially, the dimension of the light reflective element is chosen such that essentially all light of the light source that is within the critical angle, and could escape from the light guide, is received by the light reflective element (and thus enters again the light guide).

As indicated above, the light emitting surface of the light source is in optical contact with the first light guiding material.

In embodiments, this may imply that the light emitting surface is embedded in the first light guiding material.

For instance, a solid state light source may at least partly be embedded in the first light guiding material, such that the entire die is embedded in the first light guiding material. In such embodiments, essentially all light of the light sources may enter the first light guiding material (except form some light that may be reflected at the light emitting surface - first light guiding material interface.

In yet other embodiments, the light source may be configured external of the light guide, though optionally in a cavity in the light guide. In such embodiments, the light emitting surface may also be in optical contact with the light guiding material.

Also here, optical contact may especially imply that the average distance between the light emitting surface and the first light guiding material, i.e. especially the first face, 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, herein also indicated as first light transmissive (solid or liquid) material, configured between the part of the first light guiding material and the light emitting surface, such as a light transmissive adhesive. Especially, such intermediate light guiding material may have a refractive index, at e.g. 500 nm, which is essentially identical to the refractive index of the first light guiding material, or have a larger refractive index. For instance, a silicone glue may be used to arrange the light emitting surface to the part of the first light guiding material. In other embodiments, however, the light emitting surface may over essentially its entire face be in physical contact with at least part of the first light guiding material.

Therefore, in embodiments the light emitting surface is configured embedded in the first light guiding material. Alternatively, in embodiments the light emitting surface and the first face are optically coupled via a first light transmissive solid or liquid material.

Of course, when a plurality of light sources are applied, combinations of such embodiments may also be applied.

In specific embodiments, the first face of the light guide comprises one or more recessions for hosting one or more light sources, respectively.

Further, as indicated above the first element face of the light reflective element is in optical contact with part of the second face of the light guide.

Also here, optical contact may especially imply that the average distance between the second face (of the light guide) and the first element face, 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, herein also indicated as second light transmissive (solid or liquid) material, configured between the part of the first element face and the second face (of the light guide), such as a light transmissive adhesive. Especially, such intermediate light guiding material may have a refractive index, at e.g. 500 nm, which is essentially identical to the refractive index of the first element face, or have a larger refractive index. For instance, a silicone glue may be used to arrange the second face (of the light guide) to the part of the first element face. In other embodiments, however, the fist element face may over essentially its entire face be in physical contact with at least part of the second face (of the light guide).

Hence, in embodiments the first element face and the second face are optically coupled via a second light transmissive solid or liquid material.

The light source and light reflective element are configured such that a part of the light source light that is received by the light reflective element is (further) distributed in the light guide, such that at least part of the light source light that is reflected by the light reflective element is also reflected by the first face of the light guide. In this way, via total internal reflection, light of the light source that is at least partly directed perpendicular to the light guide is distributed laterally within the light guide.

Therefore, the light source, light guide, and light reflective element are especially configured such that at least part of the light source light is received by the specular reflector, and the light reflective element (and light guide) is (are) (also) configured such that at least about 40% of the light source light received by the specular reflector is reflected back under total internal reflection angles (a) with the first face of the light guide.

In this way, even though the light source may have an optical axis perpendicular to the second face, at least part of the light source light is (re)distributed over the light guide.

The light guide may be relatively thin. In embodiments, the light guide thickness (hl) may be selected from the range of up to 20 mm, such as in the range of 0.1-20 mm, like 0.5-20 mm. Especially, the light guide thickness is at maximum 10 mm, such as in the range of 0.1-5 mm, like 0.5-2 mm. The light reflective element has a second height (h2) selected from the range of at maximum 20 mm, such as in the range of 0.1-20 mm, like 0.5- 20 mm. Especially, the light reflective element has a second height (h2) of at maximum 10 mm, such as in the range of 0.1-5 mm, like 0.5-2 mm. In yet further embodiments, a height ratio R2 of the second height h2 and the light guide thickness (hl) R2=h2/hl is at maximum 1.2, such as at maximum 1, like in the range of 0.7- 1.2.

Especially, one or more of the first face and the second face include outcouple structures for facilitating outcoupling of light source light via the second face, or via the first face, or via both the first face and the second face. Especially, however, the outcoupling structures may be chosen and configured such that outcoupling via the second face is facilitated. Outcoupling structures are known in the art and may comprise one or more of refractive outcoupling structures and scattering outcoupling structures. The outcoupling structures may comprise one or more of indentation in the first face and/or second face, a pixelated pattern at one or more of the first face and the second face, etc. as known by a person skilled in the art.

Alternatively or additionally, the light source light may be coupled out from an edge of the light guide. In such embodiments, the edge may be flat, curved, have an obtuse or acute angle with one of the first face or second face, may be facetted, etc... In such embodiments the edge may have outcoupling elements. The edge may be a single edge, such as in the case of a circular light guide, like disc. However, the edge may also include a plurality of edges, such as in the case of a rectangular light guide (i.e. a light guide having a cross-sectional plane which is rectangular).

For a good propagation of light from the light guide to the reflective element, it may be desirable that the index of refraction of the second light guide material is about the same or larger than the index of refraction of the first light guide material. Therefore, in embodiments the first light guiding material has a first refractive index , wherein the second light guiding material has a second refractive index n₂, wherein a refractive index ratio R of the second refractive index n₂ and the first refractive index R=n₂/ is at least about 0.95, especially at least about 1. Hence, in embodiments the first light guiding material and the second light guiding material are the same. In yet other embodiments, the first light guiding material and the second light guiding material are different materials. In the former embodiment, the first light guide material and second light guide material may - in specific embodiments - be provided as monolithic element, i.e. a light guide with a protrusion on which the specular reflector may be arranged to provide the light guide with light reflective element.

As indicated above, the light source, light guide, and light reflective element are configured such that at least part of the light source light is received by the specular reflector; and the light reflective element is configured such that at least part of the light source light received by the specular reflector is reflected back under total internal reflection angles (a) with the first face of the light guide. Amongst others, this may be obtained in embodiments wherein the light source has a first optical axis which intersects the specular reflector. More especially, this may be obtained in embodiments wherein the light reflective element has a second optical axis, wherein the first optical axis and the second optical axis (essentially) coincide.

Light source light that enters the second light guide material may reach the specular reflector and be reflected back. When the specular reflector is not configured in optical contact with essentially the entire second element face, part of the light source light may be transmitted and escape from the reflective element. For instance, the specular reflector may have openings and may in this way, or other ways, be in optical contact with part of the entire second element face. Therefore, in embodiments the light reflective element is semi-transparent. In this way, part of the light source light received the reflective element is transmitted, and part is reflected. A partial transmission of the light source light may provide that the reflective element is not perceived as a black spot. From the light source light that is reflected by the specular reflector, at least part, especially at least 40%, is reflected such, that it is subsequently reflected under a total internal reflection angle at the first face of the light guide.

Good reflection results may be obtained in embodiments wherein the light reflective element has a second optical axis (“reflector axis”), wherein the specular reflector is two-dimensionally curved and is rotational symmetric relative to the second optical axis (02).

The reflective element may be configured to focus the light source light at the second face, for instance when the specular reflector has a Bezier curve shape. Hence, in embodiments the light source has a first optical axis (01), wherein the light reflective element is configured to reflect the light source light back to the first face and focus the light source light at the first face with an intensity maximum at the first face at a focal distance (fl) from the first optical axis (01) (from a position where the first optical axis (01) intersects the first face 201). Especially, the focal distance (fl) is selected from the range 1.25 * hl to 2.5 * hl, wherein hl is the height of the light guide. In further embodiments, the focal distance may e.g. be selected from the range of 1-10 mm. In such embodiments, the intensity maximum may have the shape of a ring.

In yet a further aspect, the invention also provides an arrangement of a light source and a light guide, wherein the light source is configured to generate light source light, wherein the light source comprises a light emitting surface via which light source light escapes from the light source; the light guide comprises a first face and a second face defining a light guide thickness (hl) with first light guiding material in between the first face and the second face; and the light emitting surface of the light source is in optical contact with the first light guiding material.

In yet a further aspect, the invention also provides an arrangement of a light guide and a light reflective element, wherein the light guide comprises a first face and a second face defining a light guide thickness (hl) with first light guiding material in between the first face and the second face; the light reflective element comprises a first element face and a second element face with second light guiding material in between the first element face and the second element face, and comprising a specular reflector in optical contact with at least part of the second element face; the first element face of the light reflective element is in optical contact with part of the second face of the light guide; and the light reflective element is configured such that at least 40 %, like especially at least 50%, even more especially at least 60%, such as at least 70, yet even more especially at least 80% of light source light of a light source (providing the light source light along an optical axis essentially coinciding with an optical axis of the specular reflector) received by the specular reflector is reflected back under total internal reflection angles (a) with the first face of the light guide.

In yet a further aspect, the invention also provides a method for providing the lighting system or a method for providing the arrangement of a light source, a light guide, and a light reflective element.

The method may start with the three different components, or may start with an arrangement of two components, to which the third component is (further) arranged. With the method, it can be avoided that the light source is at fixed position an alignment of the reflective element may be complicated or it can be avoided that the light reflective element is at a fixed position, and alignment of the light source may be complicated. However, at least it may be avoided that a pre-shaped light guide with a provision for the light source and with the second light guide material is provided, to which the specular reflector has to provided, which may be complicated. Hence, the present arrangement of the light source, the light guide, and the light reflective element may allow an assembly as desired by the producer. Hence, the system has a large flexibility in design.

Therefore, in a further aspect the invention provides a method for providing a lighting system, especially as further herein defined, wherein the method comprises:

providing a light source, a light guide, and a semi-transparent light reflective element, wherein:

aligning light reflective element relative to the light source and configuring the first element face of the light reflective element in optical contact with part of the second face of the light guide, such that at least part of the light source light is received by the specular reflector and at least 40%, like especially at least 50%, even more especially at least 60%, such as at least 70, yet even more especially at least 80%, such as at least 90% of the light source light received by the specular reflector is reflected back under total internal reflection angles (a) with the first face of the light guide. The first element face of the light reflective element has a first equivalent diameter (Dl), wherein the light emitting surface of the light source may has a second equivalent diameter (D2), wherein a critical angle is defined as 0c=arcsin(l/ni), wherein is the first refractive index of the first light guiding material, and wherein the first equivalent (Dl) complies with Dl=a*2*hl*tan(0c)+D2, wherein 0.9<a<l.l.

One may start with an arrangement wherein the light source and light guide material are already optically coupled. However, the arrangement of the light source to the light guide may also be part of the method. Therefore, in embodiments the method may further comprise configuring the light source to the light guide, to provide an arrangement of the light source and the light guide wherein the light emitting surface of the light source is in optical contact with the first light guiding material.

As indicated above, optical coupling may be achieved by using a second light transmissive solid or liquid material, such as glue or adhesive that is essentially transparent for the light source light. Hence, in further embodiments of the method, configuring the first element face of the light reflective element in optical contact with part of the second face of the light guide may comprise: providing an arrangement of the first element face and the second face wherein they are optically coupled via a second light transmissive solid or liquid material.

Instead of a glue or adhesive, also a glass frit may be applied, e.g. a low melting glass frit material. In such embodiments, the first light guide material and second light guide materials are especially inorganic materials.

The lighting system may be provided as device. For instance, a lighting device may include a housing containing the light source(s), the light guide, and the reflective element(s), wherein the second face with the light reflective element(s) is configured as window through which light source light escapes from the device.

In specific embodiments, especially, at least 80% of the light source light escapes from the second face of the light guide. However, other embodiments may also be possible, such as wherein the light escapes from an edge, or from both the first and the second face of the light guide. Optionally, downstream from the light guide (with light reflective element) further optics may be configured, such as one or more of a diffusor, a collimator, a color filter, etc.

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), 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 lighting 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, 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, (outdoor) road lighting systems, urban lighting systems, green house lighting systems, horticulture lighting, or LCD backlighting.

As indicated above, the lighting unit may be used as backlighting unit in an LCD display device. Hence, the invention provides also a LCD display device comprising the lighting unit as defined herein, configured as backlighting unit. The invention also provides in a further aspect a liquid crystal display device comprising a back lighting unit, wherein the back lighting unit comprises one or more lighting devices as defined herein.

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:

Fig. 1 schematically depict an embodiment of the system (or the arrangement of the light guide and reflector element and light source);

Figs. 2a-2c schematically depict some variants and aspects of the system;

Figs. 3a-3b schematically depict some aspects of the arrangement of the light guide and reflector element and light source;

Fig. 4 schematically depict some aspects of an embodiment of the light guide and reflector element and light source; Fig. 5 schematically depicts a disc like light guide of a system, in perspective;

Figs. 6a-6b show results of simulations; and

Fig. 7 schematically depicts a light reflective element having the shape of a Bezier curve (the light guide is not shown).

The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Amongst others, it is herein proposed to couple the light of a CoB LED into a light guide disk by embedding the LED inside the light guide, for instance by attaching the LED with an adhesive Silicone. Above the LED a protrusion with a reflective surface is attached with a specific shape.

For instance, optics are designed to create a side-ways emitting source, suitable for embedding in a light guide where the light propagates due to total internal reflection. The angular light distribution must be restricted in polar direction to enable light guiding and prevent leakage, but in the azimuthal direction it may encompass the full 360°. The polar angle is the angle of a light ray with the Z-axis of the coordinate system. The azimuthal angle is the angle of the projection of a light ray on the X-Y plane with the X-axis (see also Fig. 5).

The light source, such as a LED, like LEDs, is (are) especially in optical contact with, or embedded inside a light guide, is capped with an appropriately designed reflective optics to redirect all the emitted light into light guided modes, resulting in efficient distribution of the LED light by Total Internal Reflection across the light guide.

In embodiments, the light guide, except for outcoupling structures, may not be structured or modified, the reflector optics is attached to the light guide at a late stage of manufacturing, e.g. by additive manufacturing technology. Therefore, the system is tolerant for misalignment errors of the LED array.

From essentially every point on the surface of the LED light rays are re- directed in two azimuthally opposing directions, depending on their inclination angle. For example, rays with inclination angle smaller than 45° are directed“downward” (to one side of the light guide), and rays with larger angles are directed“upward” (to opposite side of the light guide). Hence positional color differences are eliminated. Therefore, the system has good color mixing properties.

Fig. 1 schematically depicts an embodiment of a lighting system. The lighting system 1 comprises a light source 100, a light guide 200, and a light reflective element 300. The light source 100 is configured to generate light source light 111, especially in the visible, such as white light. The light source 100, such as a solid state light source, comprises a light emitting surface 101, such as a die, via which light source light 111 escapes from the light source 100. Alternatively, the light emitting surface may be the end of an optical fiber.

The light guide 200 comprises a first face 201 and a second face 202 defining a light guide thickness hl, such as in the range of 0.1-10 mm, especially at maximum 2 mm, with first light guiding material 205 in between the first face 201 and the second face 202. The first light guiding material 205 may e.g. be glass, or silicone, or PC, or PMMA.

Reference 204 indicates an edge of the light guide 200. The edge may include several edge parts, such as in the case of a rectangular light guide.

The light reflective element 300 comprises a first element face 301 and a second element face 302 with second light guiding material 305 in between the first element face 301 and the second element face 302. The second light guiding material 305 may e.g. be glass, or silicone, or PC, or PMMA. Further, the light reflective element 300 comprises a specular reflector 320 in optical contact with at least part of the second element face 302. Here, by way of example not essentially the entire second element face is in optical contact with the specular reflector. Or, here, the specular reflector is not in optical contact with the entire second element face.

As shown, a ratio of the equivalent diameter (or“equivalent circular diameter”) of the first element face to the equivalent diameter of the second face of the light guide may be equal to or smaller than 0.1 , or even smaller.

The light emitting surface 101 of the light source 100 is in optical contact with the first light guiding material 205. Further, the first element face 301 of the light reflective element 300 is in optical contact with part of the second face 202 of the light guide 200.

As schematically shown, especially the light source 100, light guide 200, and light reflective element 300 are configured such that at least part of the light source light 111 is received by the specular reflector 320. Further, especially the light reflective element 300 is configured such that at least 40% of the light source light 111 received by the specular reflector 320 is reflected back under total internal reflection angles a with the first face 201 of the light guide 200.

In the schematically depicted embodiment, the light source 100 has a first optical axis 01 which intersects the specular reflector 320. Figs. 1 and 2a schematically show embodiments wherein the light emitting surface 101 is configured embedded in the first light guiding material 205 (see Fig. 2a, right example of light source 100, indicated with reference lOOb), or wherein the light emitting surface 101 and the first face 201 are optically coupled via a first light transmissive solid or liquid material 150 (see Fig. 1). The light emitting surface 101 and the first light guiding material may also be physically contact each other, without being embedded (see Fig. 2a, left example of light source 100, indicated with reference lOOa). For instance, the light source 100 may be held in physical contact with the first light guiding material.

Fig 1 schematically depicts an embodiment wherein the first element face 301 and the second face 202 are optically coupled via a second light transmissive solid or liquid material 250. However, alternatively the first element face 301 and the second face 202 are in physical contact with each other.

The light reflective element 300 has a second optical axis 02. This second optical 02 may essentially coincide with the first optical axis 01 of the light source, as schematically depicted in Fig. 1.

Fig. 2a also schematically depicts an embodiment wherein the first face 201 includes a recession 203, which may host at least part of the light source 100, and at least at least part of the light emitting surface 101 thereof.

Especially, the light guide thickness hl may thus be at maximum 2 mm. For instance, the light guide thickness hl may be selected from the range of 0.5-10 mm. Further, the light reflective element 300 may have a second height h2 selected from the range of 0.5- 10 mm.

Fig. 2b schematically depicts an embodiment wherein one or more of the first face 201 and the second face 202 include outcouple structures 207 for facilitating

outcoupling of light source light via the second face 202. Here, by way of example on the first face includes such light outcouple structures 207.

As shown in Figs. 2a-2b, in embodiments the specular reflector 320 is in optical contact with essentially the entire second element face. Hence, in such embodiments essentially no light may escape from the reflective element via the second element face, as light that escapes from the face, is reflected back into the reflective element 300.

Fig. 2c schematically depicts an embodiment wherein the light reflective element 300 is semi-transparent. For instance, the specular reflector 320 may include openings 323. Fig. 3a schematically depicts an embodiment of the lighting system 1, which comprises a disk-like light guide 200 with e.g. a diameter of 60 mm, a thickness hl of 6 mm. The light reflective element 300 (schematically depicted as very thin layer) has a height h2 of 4.9 mm. The light source 100 has a light emitting surface 101 of 6 mm diameter. The diameter of the reflector is 12 mm. It appears that 94% of the light source light is totally internally reflected at either the second face 202 (light with angles larger than the critical angle) or at the first face 201 after a first reflection by the light reflective element 300.

Reference A indicates a rotational axis. In this embodiment, the light guide 200 is planar and rotational symmetric relative to a rotational axis A configured

perpendicular to the second face 202.

Fig. 3b schematically depicts some aspects of the lighting system 1. The light reflective element 300 has a circular equivalent diameter Dl. The light emitting surface 101 has a circular equivalent diameter D2. Angle Q is the angle between the edge of the light emitting surface 101 to the edge of the light reflective element 300. Here it is assumed that the specular reflector 320 essentially covers the entire second element face 302.

Here, the critical angle is defined as the angle with a normal to the second face 202 under which light source light can escape from the light guide 200, and above which the light source light is reflected due to total internal reflection. Hence, the dimensions of the first element face 301 should be such that light with a smaller angle Q than the critical angle enters the light reflective element 300, whereas light with angles larger than the critical angle will essentially anyhow be total internally reflected. Hence, the dimensions of the light reflective element 300 should be such that the edge of the light reflective element 300 is essentially at about the critical angle, and preferably not much smaller, and preferably also not much larger.

The critical angle is defined as 0c=arcsin(l/ni), wherein is the first refractive index of the light guide material 205. The equivalent diameter Dl should then defined as Dl=a*2*hl*tan(0c)+D2, wherein 0.9<a<l.l, especially 0.95<a<l.05.

The shape of the light reflective element can for instance be an ellipsoidal shape, as illustrated in Fig. 4. The light guide has a thickness hl of 1 mm. The LED is placed at the origin at y = 0.0 mm. In this example, the dashed line is an ellipse, with focal points y = 0.0 mm and y_f = -1.7 mm, which makes the long axis LA about 4.3 mm. The reflective cup is filled with transparent light guide material, e.g. PMMA or silicone or glass, and is in optical contact with the light guide, which is preferably made from the same material as the reflective cup. Fig. 4, schematically illustrates propagation of the rays from the center of the LED. In this example, rays with large inclination angle from 90° to 45° are going upward and are directly captured by the light guide. They do not interact with the reflector. Rays with smaller inclination angle are reflected downward towards the second focus of the ellipsoid at position y_f = -l.7mm, in this illustration.

Reference SA indicates the short axis of the ellipse; reference LA indicates the long axis.

As schematically shown in Fig. 4, in embodiments the light source 100 has a first optical axis 01, wherein the light reflective element 300 is configured to reflect the light source light 111 back to the first face 201 and focus the light source light 111 at the first face 201 with an intensity maximum 113 at the first face 201 at a focal distance fl from the first optical axis 01 (from a position where the first optical axis 01 intersects the first face 201), wherein the focal distance fl is selected from the range of 1-10 mm.

Fig. 5 schematically depicts such embodiment in perspective. Here, the specular reflector 320 is two-dimensionally curved and is rotational symmetric relative to the second optical axis 02.

The calculated leakage can be zero for focal positions > 1.5 mm and source size < 0.2 mm. It can be <5% for a large parameter range, e.g. focal positions < 1.25 mm and source sizes < 0.6 mm. The leakage is < 10% for all sources < 1.0 mm and all focal positions > 1.0 mm. Note that all dimensions scale with the light guide thickness, here 1.0 mm.

Fig. 5 also depicts in more detail the polar angle theta, the azimuthal angle phi, the direction of a ray, which is indicated with reference s, and the C,U,Z coordinate system.

Fig. 6a shows the light leakage for different light guide thicknesses, with the lower curve indicating the disk diameter DD and the upper curve indicating the square width SW, which is alternatively herein defined as the equivalent diameter D2 of the light emitting surface. The x-axis indicates the scaled source size, that is the source size divided by the light guide thickness, and is dimensionless. It can e.g. refer to mm or cm, etc.. An example is used with a light guide with a thickness of 10 mm and a (COB) LED with a light emitting surface of 6 mm diameter (i.e. a value of 0.6 in the graph), . Then, the leakage is limited to 1.6 %. When increasing the COB size to lOmm or, equivalently, reducing the light guide to a thickness to 6 mm (1.0 in graph), the leakage increases but it stays limited to 6%. It is important to note that light leakage does not mean that the light is not lost, it is merely escaping from the light guide instead of being transported by TIR in lateral directions. Hence the negative consequences for the lighting system may be limited. Fig. 6b shows the variables as defined in the middle drawing. The top-cap indicates the height of the reflector cup, which would be 0.81 mm on top of the 1.0 mm light guide in this example. The ray angle at f is a critical dimension: it is the steepest angle of incident on the back surface of the light guide and it should be larger than the critical angle for Total Internal Reflection in the light guide. The arrow indicates the value -42°, which is achieved for a focal position of y_f = -1.7 mm in this example. Thus, for a very small source the focal point of the ellipse should be -1.7 mm or farther to prevent leakage.

Reference TC indicates the top cap height, which is herein also indicated as h2 (see Fig. 4), reference LA indicates the long axis length in mm, reference SA indicates the short axis length in mm. The short axis and the long axis are the axes of the schematically depicted ellipse. Reference a indicates the ray angle at the focal point (here f = -1.9 mm). The first y-axis scale indicates the distances in mm; the second y-axis scale indicates the angles, i.e. ray angle at f or Ra.

The reflective cup can also be defined by a Bezier curve or similar curve, as illustrated in Fig. 7. Here the reflected rays are sent almost parallel towards the back surface of the light guide (not shown), where they are Totally Internally Reflected.

In embodiments, the reflective cup can be made partially transparent to prevent disturbing dark spots.

The above-mentioned embodiments and design rules are given for e.g. a light guide of 1.0 mm thickness and LEDs with die dimensions from about 0.2- 1.0 mm. However, since the geometry is scalable, this seems particularly a good solution for micro-LED arrays, an upcoming technology, where the electrical and mechanical interconnect may not be strictly regular with high accuracy, due to the small sizes. A late-stage configuration methodology such as described in the present invention disclosure may be a very successful one. Micro-LEDs are defined as LEDs with a die size below lOOmicron.

A reflective protrusions, as defined herein, was compared with a reflective intrusion. Optically the main difference is that all the light, irrespective of the starting direction on the LED surface, is directed into the same direction of the light guide. With the reflective protrusions, roughly half of the light goes upwards and half of the light downwards, which would be advantageous for color mixing. Hence, with the intrusion: LED light emitted at small polar angles (close to normal) is reflected in the same direction as light emitted at large polar angles; with the cap: LED light emitted at small polar angle is reflected in opposite direction to light emitted at large polar angle. Further, a main difference is that the intrusions must be a-priori fabricated and aligned with the LED array with inherently strict tolerances, whereas the protrusions can be positioned at a late stage, e.g. by additive manufacturing technique, which allows for larger tolerances and flexibility.

An advantage of the proposed optical configuration is the increased efficiency by the optical contact. Especially, the (LED) light source may be embedded inside the light guide and this has a beneficial effect on the efficiency. Compared to a non-optically coupled LED, based on a plurality of simulations it appears that the light output can be up to 20% higher.

The term“plurality” refers to two or more.

The terms“substantially” or“essentially” herein, and similar terms, will be understood by the person skilled in the art. The terms“substantially” or“essentially” may also include embodiments with“entirely”,“completely”,“all”, etc. Hence, in embodiments the adjective substantially or essentially may also be removed. Where applicable, the term “substantially” or the term“essentially” 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%.

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, apparatus, or systems may herein amongst others be 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, apparatus, or systems 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 a device claim, or an apparatus claim, or a system 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.

The invention also provides a control system that may control the device, apparatus, or system, or that may execute the herein described method or process. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the device, apparatus, or system, controls one or more controllable elements of such device, apparatus, or system.

The invention further applies to a device, apparatus, or system 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 lighting system (1) comprising a light source (100), a light guide (200), and a semi-transparent light reflective element (300), wherein:

the light source (100) is configured to generate light source light (111), wherein the light source (100) comprises a light emitting surface (101) via which light source light (111) escapes from the light source (100);

the light guide (200) comprises a first face (201) and a second face (202) defining a light guide thickness (hl) with first light guiding material (205) in between the first face (201) and the second face (202);

the light reflective element (300) comprises a first element face (301) and a second element face (302) with second light guiding material (305) in between the first element face (301) and the second element face (302), and comprising a specular reflector (320) in optical contact with at least part of the second element face (302);

the light emitting surface (101) of the light source (100) is in optical contact with the first light guiding material (205);

- the first element face (301) of the light reflective element (300) is in optical contact with part of the second face (202) of the light guide (200);

the light source (100), light guide (200), and light reflective element (300) are configured such that at least part of the light source light (111) is received by the specular reflector (320); and

- the light reflective element (300) is configured such that at least 60% of the light source light (111) received by the specular reflector (320) is reflected back under total internal reflection angles (a) with the first face (201) of the light guide (200),

wherein the first element face (301) of the light reflective element (300) has a first equivalent diameter (Dl), wherein the light emitting surface (101) of the light source may (100) has a second equivalent diameter (D2), wherein a critical angle is defined as 0c=arcsin(l/ni), wherein is the first refractive index of the first light guiding material (205), and wherein the first equivalent (Dl) complies with Dl=a*2*hl*tan(0c)+D2, wherein 0.9<a<l.l.

2. The lighting system (1) according to claim 1, wherein the first light guiding material (205) has a first refractive index , wherein the second light guiding material (305) has a second refractive index n₂, wherein a refractive index ratio R of the second refractive index n2 and the first refractive index R=n₂/ is at least 1.

3. The lighting system (1) according to any one of the preceding claims, wherein 0.95<a<l.05.

4. The lighting system (1) according to any one of the preceding claims, wherein the light source (100) has a first optical axis (01) which intersects the specular reflector (320).

5. The lighting system (1) according to any one of the preceding claims 1-4, wherein the light emitting surface (101) is configured embedded in the first light guiding material (205), or wherein the light emitting surface (101) and the first face (201) are optically coupled via a first light transmissive solid or liquid material (150).

6. The lighting system (1) according to any one of the preceding claims, wherein one or more of the first face (201) and the second face (202) include outcouple structures (207) for facilitating outcoupling of light source light via the second face (202).

7. The lighting system (1) according to any one of the preceding claims, wherein the first element face (301) and the second face (202) are optically coupled via a second light transmissive solid or liquid material (250).

8. The lighting system (1) according to any one of the preceding claims, wherein the light guide (200) is planar and rotational symmetric relative to a rotational axis (A) configured perpendicular to the second face (202).

9. The lighting system (1) according to any one of the preceding claims, wherein light guide thickness (hl) is at maximum 10 mm, and wherein the light reflective element is semi-transparent, and wherein the light source (100) comprises a solid state light source, wherein the light source (100) comprises a chip-on-board light source, and wherein the light source (100) is configured to generate white light source light (111).

10. The lighting system (1) according to any one of the preceding claims, wherein the light reflective element (300) has a second optical axis (02), wherein the specular reflector (320) is two-dimensionally curved and is rotational symmetric relative to the second optical axis (02).

11. The lighting system (1) according to any one of the preceding claims, wherein the light source (100) has a first optical axis (01), wherein the light reflective element (300) is configured to reflect the light source light (111) back to the first face (201) and focus the light source light (111) at the first face (201) with an intensity maximum (113) at the first face (201) at a focal distance (fl) from the first optical axis (01), wherein the focal distance (fl) is selected from the range of 1.25 * hl to 2.5 * hl.

12. The lighting system (1) according to any one of the preceding claims, wherein light guide thickness (hl) is selected from the range of 0.5-10 mm, wherein the light reflective element (300) has a second height (h2) selected from the range of 0.5-10 mm, wherein a height ratio R2 of the second height h2 and the light guide thickness (hl)

R2=h2/hl is at maximum 1.2.

13. A method for providing the lighting system (1) according to any one of the preceding claims, wherein the method comprises:

providing a light source (100), a light guide (200), and a semi-transparent light reflective element (300), wherein:

aligning light reflective element (300) relative to the light source (100) and configuring the first element face (301) of the light reflective element (300) in optical contact with part of the second face (202) of the light guide (200), such that at least part of the light source light (111) is received by the specular reflector (320) and at least 60% of the light source light (111) received by the specular reflector (320) is reflected back under total internal reflection angles (a) with the first face (201) of the light guide (200), and the first element face (301) of the light reflective element (300) having a first equivalent diameter (Dl), wherein the light emitting surface (101) of the light source may (100) having a second equivalent diameter (D2), wherein a critical angle is defined as 0c=arcsin(l/ni), wherein is the first refractive index of the first light guiding material (205), and wherein the first equivalent (Dl) complies with Dl=a*2*hl*tan(0c)+D2, wherein 0.9<a<l.l.

14. The method according to claim 13, further comprising configuring the light source (100) to the light guide (200), to provide an arrangement of the light source (100) and the light guide (200) wherein the light emitting surface (101) of the light source (100) is in optical contact with the first light guiding material (205).

15. The method according to any one of the preceding claims 13-14, wherein configuring the first element face (301) of the light reflective element (300) in optical contact with part of the second face (202) of the light guide (200) comprises: providing an arrangement of the first element face (301) and the second face (202) wherein they are optically coupled via a second light transmissive solid or liquid material (250).