WO2014033686A2

WO2014033686A2 - Illumination device based on light guide with light diffusing particles

Info

Publication number: WO2014033686A2
Application number: PCT/IB2013/058191
Authority: WO
Inventors: Maarten Marinus Johannes Wilhelmus Van Herpen; Tim Dekker
Original assignee: Koninklijke Philips N.V.
Priority date: 2012-08-31
Filing date: 2013-08-31
Publication date: 2014-03-06
Also published as: WO2014033686A3

Abstract

A light guide (2) is disclosed. At least a portion of the light guide (2) comprises embedded light scattering and/or reflecting particles (5). The light guide (2) comprises a light in-coupling surface (3) adapted to couple light impinging on the light in- coupling surface (3) into the light guide (2), a light out-coupling surface (4) adapted to couple light out of the light guide (2), and a first region (6) and at least a second region (7), each of the first and second regions (6, 7) comprising a portion of the light out-coupling surface (4). The light guide (2) is arranged such that the proportion of light being coupled out from the first region of light travelling into the first region (6), per unit volume of the first region (6), is different from the proportion of light being coupled out from the second region (8) of light travelling into the second region (8), per unit volume of the second region (8). The degree of light that is out-coupled from the light guide at selected positions can be adapted as desired, for example to give uniform lighting or to create an aesthetic effect. An illumination device (1) comprising the light guide (2) and a luminaire comprising the illumination device (1) are also disclosed.

Description

Illumination device based on light guide with light diffusing particles

FIELD OF THE INVENTION

The present invention relates to a light guide with embedded light scattering and/or reflecting particles, and to an illumination device comprising the light guide and at least one light emitting element.

BACKGROUND OF THE INVENTION

Illumination devices comprising a light source coupled to a light guide sheet or plate, which is able to propagate light internally, redirect and out-couple the light from its surface, provide for illuminating surfaces such as shelving's, interior panels, signs and posters.

One light guide for use in such an illumination device is the ACRYLITE® EndLighten sheet from Evonik Industries. It comprises a sheet of a light conducting acrylic material in which light diffusing particles are embedded. The acrylic sheet accepts light from a light source through its end surfaces, from which the light propagates within the sheet by means of total internal reflection. The light diffusing particles embedded in the sheet redirect the travelling light such that some of it may exit the surface of the sheet, thereby giving the sheet its illuminating properties.

At different locations on the illumination surface of these light guides, the same ratio, i.e. percentage, of the propagating or travelling light is coupled out through the illumination surface. The flexibility in the amount of light that can be coupled out at different locations on the illumination surface of the light guide is thus quite low.

Moreover, the brightness at different locations on the illumination surface of such a light guide is dependent on the distance that the light has to travel or propagate to arrive at the respective locations, due to light losses in the light guide. As a result, the light output over the illumination surface can become non-uniform, especially when a relatively large light guide is used and/or a bright output is desired. Also, it has the result that light guides, for example of irregular or triangular shape, in which the light travels different distances, may be unevenly lighted. One solution to achieve uniformity is to decrease the number of light scattering or reflecting particles, and significantly increase the light source output. In that case most of the light is not out-coupled at all, and is lost on the other side of the light guide. The result is that the light output is more uniform, because the dependence on distance is much less, but the overall system is optically very inefficient.

SUMMARY OF THE INVENTION

Light propagating in light guides may be out-coupled by means of light out- coupling structures on the surface of the light guide. Such light out-coupling structures are for instance comprised of paint dots, scratches or molded microstructures that are arranged on the illumination surface of the light guide. They are able to extract light that impinge upon them from within the light guide such that it exits the surface of the light guide. Such light out-coupling structures are however visible to a viewer and may therefore degrade the visual impression of the light guide.

In view of the above discussion, a concern of the present invention is to provide a light guide and an illumination device in which the amount of light that is out- coupled from the light guide at selected positions can be adapted as desired.

Another related concern of the present invention is to provide a light guide and an illumination device with a more uniform lighting, e.g. where the intensity and/or brightness of the light that is out-coupled from the light guide is more uniform or

homogeneous than the intensity and/or brightness of the light out-coupled from the light guide described in the background section, or where the intensity and/or brightness of the light that is out-coupled from the light guide is even completely or nearly completely uniform or homogeneous.

Another concern of the present invention is to provide a light guide and an illumination device with an increasingly uniform lighting, e.g. where the intensity and/or brightness of the light that is out-coupled from the light guide is more uniform or

homogeneous than the intensity and/or brightness of the light out-coupled from the light guide described in the background section, while alleviating or even eliminating need for a corresponding increase in light source output or power.

To address at least one of these concerns and other concerns, a light guide in accordance with the independent claim is provided. Preferred embodiments are defined by the dependent claims. According to a first aspect of the present invention, there is provided a light guide of which at least a portion comprises embedded light scattering and/or light reflecting particles The light guide comprises a light in-coupling surface adapted to couple light impinging on the light in-coupling surface into the light guide, and a light out-coupling surface adapted to couple light out of the light guide. The light guide further comprises a first region for coupling out a first proportion of light travelling within the first region, per unit volume of the first region, and a second region for coupling out a second proportion of light travelling within the second region, per unit volume of the second region. The light guide is arranged such that the first proportion of light is different from the second proportion of light.

The present invention is based on a realization that the degree of light that is out-coupled from the light guide at different locations or positions of the light guide, e.g. via a light out-coupling surface of the light guide, is for example dependent on the concentration of embedded light scattering and/or reflecting particles, elements and/or other structures at that the respective locations or positions in the light guide. By arranging the light guide such that different regions of the light guide have different concentrations of light scattering and/or diffusing particles it is thereby possible to adapt the light guide such that the degree and the amount of light that is out-coupled at those regions is according to different requirements, and thus to adapt the brightness and/or intensity of the light in those regions as desired or required. This can for example be made in order to highlight a chosen region on the light out- coupling surface of the light guide that is of special interest, create a certain desired aesthetic effect or achieve uniform lighting across the light out-coupling surface of the light guide. In the latter case, light losses occurring in the light guide as a function of the distance that the light has to travel or propagate within the light guide in order to arrive at a certain position can be compensated for by adjusting the concentration of embedded light scattering and/or reflecting particles at that position. Typically, in order to achieve uniform lighting, the concentration of light scattering and/or reflecting particles at different positions of the light guide is arranged to vary with the distance between the respective positions and the light in- coupling surface, such that the concentration of light scattering and/or reflecting particles at a position increases with increasing distance of the position from the light in-coupling surface. Alternatively or optionally to having regions with different concentrations of embedded light scattering and/or reflecting particles, the light guide can have light out-coupling structures arranged on its light out-coupling surface. The light out-coupling structures are arranged to out-couple light, which as it travels within the light guide impinges on the light out-coupling structures, such that the light exits the light guide via the light out-coupling surface of the light guide. Thus, the light guide can comprise two types of elements that redirect the light traveling within the light guide, such that it exits the light out-coupling surface; light scattering and/or reflecting particles embedded in the light guide as well as light out-coupling structures on the surface of the light guide. By arranging light out-coupling structures on the light out-coupling surface of the light guide it is possible to increase and/or adjust the degree and the amount of light that is out-coupled from the light guide. Moreover, by using light out- coupling structures on the surface of a light guide with embedded light scattering and/or reflecting particles, fewer light out-coupling structures per unit area are required, as compared to light guides without embedded light scattering and/or reflecting particles, in order to achieve the same degree of out-coupling of the light. Since light out-coupling structures are generally visible to a viewer, the fewer there is of such light out-coupling structures per unit area on the light out-coupling surface of the light guide, the better the visual impression of the light guide to the viewer.

The regions of the light guide, i.e. the first and the at least a second regions of the light guide, may be different and possibly non-overlapping, and/or of the same or substantially the same size.

For example, the first and the at least a second regions of the light guide may have the same or substantially the same size, and the light guide can be arranged such that the proportion of light being coupled out from the first region of light travelling into the first region is different from the proportion of light being coupled out from the second region of light travelling into the second region.

The term "concentration" as referred to herein with respect to light scattering and/or reflecting particles, elements and/or structures embedded in a light guide denotes the number of light scattering and/or reflecting particles per unit volume of the light guide.

The term "degree of light that is out-coupled", as referred to herein, indicates the proportion, i.e. ratio or percentage, of the light within a light guide passing a certain position or location in the light guide that is coupled out at that position or location.

The term "amount of light that is out-coupled", as referred to herein, indicates the quantity of light of the light within a light guide passing a certain position or location in the light guide that is coupled out at that position or location.

By the first and the second concentrations of embedded light scattering and/or reflecting particles being "different", it may be referred to the first and second concentrations of embedded light scattering and/or reflecting particles being such that light out-coupled from the light out-coupling surface of the light guide originating from the first and second regions, respectively, have a difference in brightness and/or intensity that can be perceived by a viewer. In alternative or optionally, by the first and the second concentrations of embedded light scattering and/or reflecting particles being "different", it may be referred to the first and second concentrations of embedded light scattering and/or reflecting particles being such that light out-coupled from the light out-coupling surface have a more uniform brightness over the light out-coupling surface, as perceived by a viewer of, than light out-coupled from a corresponding light guide with a homogeneous concentration of light scattering and/or reflecting particles throughout the light guide. According to embodiments of the present invention, the first and the second concentrations of embedded light scattering and/or reflecting particles differ by a few percent, or ten percent or more. According to other embodiments of the present invention, the first concentration of embedded light scattering and/or reflecting particles and the second concentration of embedded light scattering and/or reflecting particles are both non-zero, and the first concentration of embedded light scattering and/or reflecting particles is a multiple or fraction of the second concentration of embedded light scattering and/or reflecting particles, or vice versa.

According to an embodiment of the present invention, the first region has a first concentration of embedded light scattering and/or reflecting particles and the at least a second region has a second concentration of embedded light scattering and/or reflecting particles, where the first and second concentrations are different and at least one of the first and second concentrations is larger than zero. Thereby the proportion of light being coupled out from the first region of light travelling into the first region, per unit volume of the first region, is different from the proportion of light being coupled out from the second region of light travelling into the second region, per unit volume of the second region.

According to another embodiment of the present invention, which may be combined with the embodiment described immediately above, the light guide comprises a plurality of light out-coupling structures arranged on the light out-coupling surface. The number of light out-coupling structures per unit area of the light out-coupling surface of the first region is different from the number of light out-coupling structures per unit area of the light out-coupling surface of the at least a second region. At least one of the number of light out-coupling structures per unit area of the light out-coupling surface of the first region and the number of light out-coupling structures per unit area of the light out-coupling surface of the at least a second region is larger than zero. Thereby the proportion of light being coupled out from the first region of light travelling into the first region, per unit volume of the first region, is different from the proportion of light being coupled out from the second region of light travelling into the second region, per unit volume of the second region.

By arranging the light guide to have different regions with different numbers of light out-coupling structures per unit area of the light out-coupling surface, it is possible to adapt the degree and amount of light that is out-coupled from the respective regions to different requirements or desires, and thus to adapt the brightness and/or intensity of the light out-coupled from the respective regions as desired or required. This can for example be made in order to highlight a chosen region on the light out-coupling surface of the light guide that is of special interest, create a certain desired aesthetic effect or achieve uniform lighting across the light out-coupling surface of the light guide. In the latter case, light losses occurring in the light guide as a function of the distance that the light has to travel or propagate within the light guide in order to arrive at a certain position can be compensated for by adjusting the number of light out-coupling structures per unit area of the light out- coupling surface at that position. Typically, in order to achieve uniform lighting, the number of light out-coupling structures per unit area at a position of the light guide is arranged to vary with the distance of the position from the light in-coupling surface, such that the number of light out-coupling structures per unit area at a position increases with increasing distance of the position from the light in-coupling surface.

The light guide according to the present invention comprises embedded light scattering and/or reflecting particles. The light guide is arranged to enable propagation of light coupled into it by means of total internal reflection (TIR). The light guide comprises a material through which light can propagate, in which material the light scattering and/or reflecting particles are embedded. The material is preferably a transparent material. The term "transparency", as referred to herein, is the physical property of allowing light to pass through the material without being scattered. In different embodiments, the light guide comprises a material selected from poly(methylmethacrylate) (PMMA), polycarbonate, glass and/or silicone rubber. PMMA is sometimes called acrylic glass. A light guide may comprise more than one of these materials. A combination of an acrylic material, such as PMMA, and silicone rubber is advantageous, since a good optical contact between the acrylic material and the silicone rubber is relatively easily achieved. For example, a sheet of an acrylic material comprising light scattering and/or reflecting particles may be embedded in liquid silicone, after which the silicone is cured. The resulting light guide is a silicone sheet comprising an embedded acrylic sheet with light scattering and/or reflecting particles. The acrylic sheet within the silicone sheet cannot be perceived by a viewer until light enters the acrylic sheet and reflects upon the light scattering and/or reflecting particles.

The light guide may have various forms, such as a plate, a rod or a fiber. The shape of the light guide may be substantially regular or irregular. At least a portion of the outer surface of the light guide, e.g. the out-coupling surface, may be smooth. In other example, at least a portion of the outer surface of the light guide is rough, i.e. not smooth. Preferably the outer surface is smooth, such that a minimum of light exits through the outer surface. The light guide may have a rectangular, triangular or circular shape or may have any other regular or irregular shape.

According to an embodiment of the present invention, light out-coupling structures are arranged on the light out-coupling surface of the light guide. The light out- coupling structures are arranged to be able to extract light that impinge upon them from within the light guide, such that the light is out-coupled via the out-coupling surface of the light guide. The light out-coupling structures may for instance comprise paint dots, scratches or molded micro structures that are arranged on the light out-coupling surface of the light guide.

In an embodiment the present invention, the first region has a first concentration of light scattering and/or reflecting particles and the at least a second region has a second concentration, different from the first concentration, of light scattering and/or reflecting particles. According to another embodiment of the present invention, the first region has a first number of light out-coupling structures per unit area on the light out- coupling surface and the at least a second region has a second number, different from the first number, of light out-coupling structures per unit area on the light out-coupling surface.

In one embodiment of the present invention, the light guide is arranged such that the first region and the at least a second region are arranged relatively to each other such that at least some of the light coupled into the light guide travels to the at least a second region via the first region, or vice versa. In other words, the first region and the at least a second region are arranged serially and in optical contact with one another. By serially arranged is meant that the regions are arranged "side-by-side", such that at least some light travelling within the light guide is able to travel from one region to the other.

In embodiments of the present invention, the light guide comprises more than two regions having different concentrations of light scattering and/or reflecting particles, and/or having different numbers of light out-coupling structures per unit area of the light out- coupling surface of the light guide., The light guide may for instance comprise 3, 4 or 5 regions, or between 5-10, 10-15, 10-20 regions, or even up to 30, 40 or 50 or more regions having different concentrations of light scattering and/or reflecting particles or having different numbers of light out-coupling structures per unit area of the light out-coupling surface of the light guide. A larger number of regions with different concentrations of light scattering and/or reflecting particles, and/or different numbers of light out-coupling structures per unit area of the light out-coupling surface of the light guide, may provide for a more gradual transition in the degree of out-coupling of light from the light guide. In one embodiment, the light guide is arranged such that there is a smooth gradient in the concentration of light scattering and/or reflecting particles, and/ or in the number of light out- coupling structures per unit area of the light out-coupling surface of the light guide, across at least a part of the light guide, thereby providing a smooth and gradual transition or smooth variation in the degree of light that is out-coupled across the light guide. According to such an embodiment, there is thus provided a number of continuously arranged regions having different concentrations of light scattering and/or reflecting particles and/or having different numbers of light out-coupling structures per unit area.

In one embodiment according to the present invention, each of the first region and the second region, or all regions, has a concentration of light scattering and/or reflecting particles that is larger than zero (> 0). That is, all regions may comprise at least a small concentration of light scattering and/or reflecting particles. In a similar embodiment according to the present invention, each of the first region and the second region, or all regions, has a number of light out-coupling structures per unit area of the light out-coupling surface that is larger than zero (> 0). That is, all regions may comprise at least a small number of light out-coupling structures per unit area of the light out-coupling surface.

In another embodiment according to the present invention, one of the first concentration of light scattering and/or reflecting particles and the second concentration of light scattering and or reflecting particles is zero or substantially zero (0). That is, at least one of the first region and the at least a second region is substantially void of light scattering and/or reflecting particles. In a similar embodiment according to the present invention, one of the number of light out-coupling structures per unit area of the light out-coupling surface of the first region and the number of light out-coupling structures per unit area of the light out- coupling surface of the at least a second region is zero or substantially zero (0). That is, the light out-coupling surface of at least one of the first region and the at least a second region is substantially void of light out-coupling structures. Embodiments comprising regions that are substantially void of light scattering and/or reflecting particles, and/or of light out-coupling structures on the out-coupling surface are particularly suited for creating decorative and/or aesthetic effects, for example to highlight a certain region of the light out-coupling surface of the light guide or to create an illuminated area of a certain shape.

In such an embodiment according to the present invention, a first region of the light guide comprises a concentration of light scattering and/or reflecting particles that is substantially zero while a second region comprises light scattering and/or reflecting particles of a concentration that is larger than zero and that enables out-coupling of light from the light out-coupling surface to an extent such that the out-coupled light is visible to a viewer. The first region, which is substantially free or void of light scattering and/or reflecting particles, is transparent and does not output any light, while the second region, comprising light scattering and/or reflecting particles of a sufficiently high concentration, does output light. Thus, having a light guide that is partly substantially void of light scattering and/or reflecting particles and partly comprises light scattering and/or reflecting particles of a concentration enabling visible output of light from the light out-coupling surface, enables creation of a light guide having a partly transparent and unlit surface and having an illuminated area of a predetermined shape, for example the shape of a star, of a circle, of text or of a logotype.

Likewise, in an embodiment according to the present invention, a first region of the light guide comprises a number of light out-coupling structures on the out-coupling surface per unit area that is zero or substantially zero while a second region comprises a number of light out-coupling structures on the out-coupling surface per unit area that is larger than zero and that enables out-coupling of light from the light out-coupling surface to an extent such that the out-coupled light is visible to a viewer of the illumination device. The first region, which comprises light scattering and/or reflecting particles but is substantially free of light out-coupling structures on the out-coupling surface, out-couples light to a small degree, while the second region, comprising both light scattering and/or reflecting particles and light out-coupling structures on the out-coupling surface, out-couples light to a higher degree. Thus, having a light guide that is partly substantially void of light out-coupling structures and partly comprises light out-coupling structures on the light out-coupling surface enables creation of a light guide having an illuminating surface, i.e. out-coupling surface, with areas of increased light intensity and/or brightness compared to other areas of the surface. This may for instance be used to highlight selected areas of the illuminating surface of a predetermined shape, for example the shape of a star, of a circle, of text or of a logotype. Similar effects may also be achieved, where it is desired to have different amounts of light out-coupled at different regions of the light out-coupling surface of the light guide, in embodiments where the first region and the second region, or all regions, have a

concentration of light scattering and/or reflecting particles that is larger than zero, or where the first region and the second region, or all regions, have a number of light out-coupling structures per unit area of the light out-coupling surface that is larger than zero (>0). In such embodiments, the difference in concentration of light scattering and/or reflecting particles, and/or in number of light out-coupling structures per unit area of the light out-coupling surface between the different regions, is large enough to create a visible difference in the brightness of the light that is out-coupled at the respective regions. All regions of the light out-coupling surface of the light guide are then illuminating, but one or more regions are brighter than the others, for example to highlight a logo or to create some other desired aesthetic effect.

In an embodiment according to the present invention, the first and second regions are in optical contact with each other. With "optical contact" it is in this context meant that these regions of the light guide are joined together without an air gap in-between.

One advantage of the present invention is that the light coupled out from the light guide can be arranged to be uniform over the light out-coupling surface. For example, the concentration of light scattering and/or reflecting particles, and/or the number of light out-coupling structures per unit area of the light out-coupling surface of the light guide, in different regions of the light guide may be arranged such that uniform output of light is achieved over the light out-coupling surface of the light guide. By uniform output of light is meant that the brightness and/or intensity of the light is uniform, i.e. has the same or substantially the same magnitude, across the light out-coupling surface of the light guide.

For a light guide comprising a uniform concentration of light scattering and/or reflecting particles across the light guide body, the amount of light that reaches a position in the light guide decreases with the distance that the light has to travel or propagate within the light guide to arrive at the position, since some light is coupled out along the way and due to light losses in the light guide. Therefore, the brightness at each position of such a light guide is dependent on the distance that the light has to travel or propagate within the light guide to arrive at that position that is the distance of the position with regard to the light in-coupling surface of the light guide. The light losses can be compensated for by adjusting the concentration of embedded light scattering and/or reflecting particles and/or the number of light out-coupling structures per unit area of the light out-coupling surface of the light guide, at a certain position or location in the light guide, in dependence of the distance that the light has to travel or propagate to arrive at the position or location. By increasing the concentration of light scattering and/or reflecting particles, and/or the number of light out-coupling structures per unit area of the light out-coupling surface of the light guide, at a position or location in the light guide, the degree of light that is coupled out at that position or location is increased. Thus, although the amount of light that reaches a position in the light guide decreases with the distance from the light in-coupling surface, the proportion of that light that is out-coupled via the light out-coupling surface can be arranged to increase with the distance from the light in-coupling surface, by increasing the concentration of light scattering and/or reflecting particles in the light guide, and/or the number of light out-coupling structures per unit area of the light out-coupling surface of the light guide, with the distance from the light in-coupling surface.

In one embodiment of the present invention, the first region is closer to the light in-coupling surface than the at least a second region and the light guide is arranged such that the first concentration of embedded light scattering and/or reflecting particles is smaller than the second concentration of embedded light scattering and/or reflecting particles. In other words, the second region is more distant to the light out-coupling surface and comprises a larger concentration of embedded light scattering and/or reflecting structures than the first region, in order to compensate for the light loss occurring as the light travels to this more distant region.

Alternatively or optionally, in another embodiment of the present invention, the first region is closer to the in-coupling surface than the at least a second region and the light guide is arranged such that the number of light out-coupling structures per unit area of the light out-coupling surface of the first region is smaller than the number of light out- coupling structures per unit area of the light out-coupling surface of the at least a second region. In other words, the second region is more distant to the light out-coupling surface and comprises a larger number of light out-coupling structures per unit area of the light out- coupling surface than the first region, in order to compensate for the light loss occurring as the light travels to this more distant region. This embodiment has the further advantage that it can be used to facilitate arrangement to achieve uniform out-coupling of light also for light guides that are not rectangular. In light guides having embedded light scattering and/or reflecting particles, and having shapes in which the light has to travel or propagate different distances within the light guide in order to reach the end of the light guide opposite the light in-coupling surface, it is often difficult to achieve uniform out-coupling of light over the light out-coupling surface. This is due to that it is difficult to arrange an appropriate variation in the concentration of embedded light scattering and/or reflecting particles within the light guide to compensate for the light losses at the different distances that the light travels or propagates. By using varying numbers of light out-coupling structures per unit area on the light out-coupling surface of such a light guide, such compensation is more easily achieved.

In one embodiment of the present invention, the light guide is arranged such that the concentration of embedded light scattering and/or reflecting particles at least partly depends on the distance from the light in-coupling surface in at least a portion of the light guide. The light guide may for instance be arranged such that the concentration of embedded light scattering and/or reflecting particles in the first region and the at least a second region, respectively, at least partly depend on the distance of the first region and the at least a second region, respectively, from the light in-coupling surface. The concentration of light scattering and/or reflecting particles may for instance be arranged to vary exponentially with the distance to the light in-coupling surface, in order to compensate for exponential light loss in the light guide, with the distance from the light in-coupling surface. The concentration of light scattering and/or reflecting particles may be arranged to vary with the distance of the first and second regions from the light in-coupling surface, such that a desired uniformity in intensity and/or brightness of the out-coupled light across the light out-coupling surface is achieved.

In one embodiment of the present invention, the light guide is arranged such that the number of light out-coupling structures per unit area of the light out-coupling surface at least partly depends on the distance from the light in-coupling surface for at least a portion of the light out-coupling surface. The number of light out-coupling structures per unit area of the light out-coupling surface of the first region and the number of light out-coupling structures per unit area of the light out-coupling surface of the at least a second region, respectively, may at least partly depend on the distance of the first region and the at least a second region, respectively, from the light in-coupling surface. The number of light out- coupling structures per unit area of the light out-coupling surface may for instance be arranged to vary exponentially with the distance to the light in-coupling surface, in order to compensate for exponential light loss in the light guide, with the distance from the light in- coupling surface. The number of light out-coupling structures per unit area of the light out- coupling surface may be arranged to vary with the distance of the first and second regions from the light in-coupling surface, such that a desired uniformity in intensity and/or brightness of the out-coupled light across the light out-coupling surface is achieved. In one embodiment of the present invention, the concentration of light scattering and/or reflecting particles in a region, and/or the number of light out-coupling structures per unit area on the light out-coupling surface of the region, is adapted depending on the light intensity of the light emitted from at least one light emitting element providing light to the region and/or on the shape of the light guide.

For example, in cases where the light guide has a shape, such as a triangular or irregular shape, in which the distance that the light travels in the light guide varies across the light guide, the light losses in the light guide may vary at different positions or locations across the light guide, depending on the distance of the positions or locations from the light in-coupling surface. The concentration of light scattering and/or reflecting particles at a position or a region, and/or the number of light out-coupling structures per unit area on the light out-coupling surface of the position or region, may be adapted to facilitate uniform lighting of a light guide of such an irregular shape.

Also, for such light guides it may be advantageous to use a plurality of light emitting elements, each emitting light of a different intensity, to couple light into the light guide. Light emitting elements that emit low intensity light are preferably arranged at locations of the light in-coupling surface where the in-coupled light travels a small distance into the light guide, i.e. where the width of the light guide is small. Light emitting elements that emit high intensity light are preferably arranged at locations of the light in-coupling surface where the in-coupled light travels a longer distance into the light guide, i.e. where the width of the light guide is large. In order to compensate for the differences in intensity of the light that is in-coupled at the different locations of the light in-coupling surface, light out- coupling structures may be arranged on the light out-coupling surface of the light guide. A high number of light out-coupling structures may be arranged at regions of the light guide having a small width, while a smaller number of light out-coupling structures per unit area may be arranged at regions of the light guide having a large width, such that light is uniformly out-coupled from the out-coupling surface of the light guide. Similarly, the concentration of light scattering and/or reflecting particles at a narrow region of the light guide, and at which low intensity light is in-coupled, may be arranged to be higher than the concentration at a wide region of the light guide, at which high intensity light is in-coupled.

In embodiments of the present invention, the light guide comprises a light guide member, or one light guide member or a single light guide member, comprising the first region and the at least a second region. Such a light guide member may comprise at least two regions with different concentrations of light scattering and/or reflecting particles. The concentration of embedded light scattering and/or reflecting particles may thus vary within the one light guide member. Such a variation of concentrations of embedded light scattering and/or reflecting particles within a light guide member may be achieved, for example, by not mixing the material with dispersed light scattering and/or reflecting particles well enough before the material is cured. It may alternatively be achieved by combining a material comprising dispersed light scattering and/or reflecting particles with a material that is void of light scattering and or reflecting particles, and not mixing the combination well enough so as to avoid equalization of the concentration. Still another way to manufacture such a light guide member is by mixing a material comprising dispersed light scattering and/or reflecting particles with a material that is void of light scattering and/or reflecting particles as the material is cast to the shape of the light guide member. As the materials pour onto the light guide mould, they are mixed in a ratio that is controlled and may be varied during the pouring. Similarly, light out-coupling structures, such as paint dots or surface scratches, may be arranged such that at least two regions on the light out-coupling surface of the single light guide member comprise different numbers of light out-coupling structures per unit area of the light out-coupling surface.

In another embodiment of the first present invention, the light guide comprises a first light guide member and at least a second light guide member, the first light guide member comprising the first region and the at least a second light guide member comprising the at least a second region, wherein each of the light guide members is arranged to be in optical contact with at least one of the other light guide members. The light guide may comprise additional light guide members comprising additional regions comprising different concentrations of light scattering and/or reflecting particles, and/ or different numbers of light out-coupling structures per unit area of the out-coupling surface. The manufacture of light guides, having two or more regions comprising different concentrations of light scattering and/or reflecting particles, can be easier when the two regions are arranged in separate light guide members as compared to when the two regions are arranged in a common light guide member. A number of light guide members, each comprising a selected and uniform concentration of light scattering and/or reflecting particles may be manufactured in a first step. At least two such light guide members, comprising different and selected concentrations of light scattering and/or reflecting particles, can then be joined in the light guide, such that the light guide comprises at least two regions comprising different concentrations of light scattering and/or reflecting particles. In one embodiment, the concentration of light scattering and/or reflecting particles, the number per unit area of the out-coupling surface of light out-coupling structures in a light guide member, and/or the width of the light guide member, may be selected in order to achieve uniform output of light from the light out-coupling surface. For example, in case the light loss in the light guide is exponential with the distance to the light in-coupling surface, a number of light guide members of a selected and preferably small width may be serially arranged with respect to the light in-coupling surface. The concentration of light scattering and/or reflecting particles, and/or the number per unit area of the out-coupling surface of light out-coupling structures, is then arranged to increase exponentially over the light guide members and with their distance to the light in-coupling surface, in order to achieve uniform light.

The cross section of a light guide member can be rectangular or can have any other shape, such as wedge shaped, as is described below with reference to Figure 4A. Two or more of such light guide members may be joined such that the resulting light guide has a rectangular cross-section.

The light guide members are joined such that a sufficient optical contact is achieved between the respective light guide members, and preferably such that the joined light guide members substantially has the same or similar light transport capability and/or capacity as a single light guide member. The joint between the light guide members is preferably a transparent joint. Methods for joining acrylic light guide members are for

®

instance described in the pamphlet "Working with Acrylite acrylic sheet", distributed by CYRO Industries, Rockaway, NJ 07866, USA, see chapter "Joining ACRYLITE acrylic sheet".

The light guide may for instance comprise a number of regions having different concentrations of light scattering and/or reflecting particles, and also including light out-coupling structures arranged on the light out-coupling surface of the light guide.

According to a second aspect of the present invention, there is provided an illumination device comprising a light guide according to the present invention and at least one light emitting element arranged such that at least some light emitted by it is coupled into the light guide via the light in-coupling surface.

The illumination device of the present invention comprises one or two or a plurality of, i.e. two or more, light emitting elements. The light emitting element or elements may in principle comprise any kind of element that is able to generate and emit light. For example, the light emitting elements may comprise light emitting diodes, LEDs. RGB LEDs are advantageously used to enable dynamic color light output from the illumination device. In embodiments of the illumination device comprising a plurality, i.e. two or more, of light emitting elements, the light emitting elements may be of the same type or different types.

The at least one light emitting element emits light during use. The light guide accepts light from the at least one light emitting element through or via the at least one light in-coupling surface, from which the light propagates within the light guide by means of total internal reflection. The light scattering and/or reflecting particles embedded in the light guide redirect the light propagating within the light guide such that at least some of it may exit a surface, e.g. light out-coupling surface, of the light guide, thereby giving the light guide at least some of its illuminating properties. According to an embodiment of the present invention, light out-coupling structures arranged on the light out-coupling surface of the light guide additionally redirect some of the light propagating within the light guide such that at least some of it may exit the light out-coupling surface, thereby further contributing to the illuminating properties of the light guide.

The first region and the at least a second region of the light guide may be arranged in relation to a light emitting element such that at least some of the light that is emitted from the light emitting element and is coupled into the light guide may travel to the second region via the first region, or vice versa. The first region and the at least a second region may alternatively be arranged in relation to a first light emitting element and a second light emitting element such that at least some of the light that is emitted from the first light emitting element and is coupled into the light guide may travel to the second region via the first region and such that light that is emitted from the second light emitting element and is coupled into the light guide may travel to the first region via the second region. The first and second light emitting elements may be arranged to couple light into a light in-coupling surface on the same side of the light guide, or alternatively be arranged to couple light into light in-coupling surfaces on mutually opposite sides of the light guide.

An illumination device according to the present invention may be used for illuminating surfaces such as shelves, interior panels, thin profile signs and poster panels, etc. The illumination device is may advantageously be comprised in a luminaire, such as a consumer luminaire used for general lighting of a space, such as a home.

According to a third aspect of the present invention, there is provided a luminaire comprising an illumination device according to the present invention.

According to a fourth aspect of the present invention, there is provided a light guide comprising embedded light scattering and/or reflecting particles, a light in-coupling surface adapted to couple light impinging on the light in-coupling surface into the light guide, and a light out-coupling surface adapted to couple light out of the light guide. The light guide comprises a plurality of light out-coupling structures arranged on the light out-coupling surface of the light guide. Each light out-coupling structure of the plurality of light out- coupling structures is adapted to couple out light impinging on the light out-coupling structure from the light guide.

According to a fifth aspect of the present invention, there is provided an illumination device comprising a light guide according to the fourth aspect of the present invention and at least one light emitting element arranged such that at least some light emitted by it is coupled into the light guide via the light in-coupling surface of the light guide.

According to a sixth aspect of the present invention, there is provided a luminaire comprising an illumination device according to the fifth aspect of the present invention.

Further objects and advantages of the present invention are described in the following by means of exemplifying embodiments.

It is noted that the present invention relates to all possible combinations of features recited in the claims. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplifying embodiments of the invention will be described below with reference to the accompanying drawings, wherein:

Figure 1 schematically depicts an illumination device according to an embodiment of the present invention, comprising regions with different concentrations of light scattering and/or reflecting particles.

Figure 2 schematically depicts an illumination device according to an embodiment of the present invention, comprising regions with different concentrations of light scattering and/or reflecting particles, wherein the concentration in at least one region is zero or substantially zero. Figure 3A-3B schematically depict embodiments of illumination devices according to the present invention, comprising regions with different concentrations of light scattering and/or reflecting particles.

Figures 4A-4B schematically depict cross-sectional side views of illumination devices according to embodiments of the present invention.

Figure 5 schematically depicts an illumination device according to an embodiment of the present invention, comprising regions with different numbers of light out- coupling structures per unit area of a light out-coupling surface.

Figures 6A-6B schematically depict embodiments of illumination devices according to the present invention, comprising regions with different numbers of light out- coupling structures per unit area of a light out-coupling surface, wherein the number of light out-coupling structures per unit area in at least one region is zero or substantially zero.

Figure 7 schematically depicts an illumination device according to an embodiment of the present invention, comprising light emitting elements that emit light of different intensities and a triangular light guide comprising regions with different numbers of light out-coupling structures per unit area of a light out-coupling surface.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments of the present invention are shown. The present 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 by way of example so that this disclosure will convey the scope of the invention to those skilled in the art. Furthermore, like numbers refer to the same or similar elements or components throughout.

Figure 1 schematically depicts an illumination device 1, arranged to generate output light 12. The illumination device 1 comprises a plurality of light emitting elements 10 and a light guide 2 comprising embedded light scattering and/or emitting particles 5. The light emitting elements 10 are arranged such that at least some of the light emitted by them is coupled into the light guide 2.

The light emitting elements 6 may in principle comprise any kind of element that is able to generate and emit light. For example, the light emitting elements 6 may comprise light emitting diodes, LEDs. RGB LEDs are advantageously used to enable dynamic color light output from the illumination device 1. The plurality, i.e. two or more, of light emitting elements 6 shown in Figure 1 may be of the same type or different types. Other embodiments of the illumination device according to the present invention may comprise only one light emitting element.

The light guide 2 shown in Figure 1 comprises a waveguide which is arranged to receive input light 11 through or via a light in-coupling surface 3 and to out-couple the light through or via a light out-coupling surface 4. In a preferred embodiment, as shown in Figure 1, the light guide 2 is substantially plate shaped, having edge surfaces along its edges, as well as a top surface and a bottom surface. The top and bottom surfaces are parallel. A light in-coupling surface 3 is arranged on at least one of the edge surfaces and is

perpendicular to the top and bottom surfaces. The light out-coupling surface 4 is arranged on the top surface. The light guide 2 may alternatively be arranged in various other ways. For example it may have a curved configuration, having curved top and bottom surfaces, have a more rod-like shape, be triangular, circular or have any other regular or irregular shape. Alternatively, the light out-coupling surface 4 may be arranged on both the top and bottom surfaces or only on the bottom surface.

The light guide 2 is arranged to enable propagation of light coupled into it by means of total internal reflection (TIR). It comprises a material through which light can propagate. The material is preferably a transparent material. Examples of such materials include transparent acrylic materials such as poly(methylmethacrylate) (PMMA), polycarbonate, glass and silicon rubber.

Light scattering and/or reflecting particles 5 are embedded in the wave guide. These particles 5 enable out-coupling of the light as output light 12. The light scattering and/or reflecting particles 5 redirect light beams that impinge upon them, and may redirect at least some of the light beams towards the light out-coupling surface 4, at an angle of incidence that is smaller than the critical angle for TIR, thus enabling the light beam to be out-coupled from the light out-coupling surface 4 of the light guide 2.

The light guide 2 comprises several regions 6, 7, 8, of which at least two regions comprise different concentrations of the embedded light scattering and/or reflecting particles. In Figure 1, region 7 comprises a higher concentration of light scattering and/or reflecting particles than regions 6 and 8 and therefore out-couple light to a higher degree per unit volume of the region than regions 6 and 8. That is, a higher proportion of the light reaching region 7 is out-coupled from the light guide 2 from region 7, per unit volume of region 7, than the proportion of light reaching the regions 6 and 8 and there being out- coupled from the light guide 2, per unit volume of the respective regions 6 and 8. The quantity of light 12 that is out-coupled through or via the light out-coupling surface 4 can thus be arranged to be higher for region 7 than regions 6 and 8, such that the light out- coupled from region 7 has a higher brightness and/or intensity than the light out-coupled from regions 6 and 8.

Alternatively, the concentration of embedded light scattering and/or emitting particles 5 within each region 6, 7, 8 can be arranged such that the light 12 that is out-coupled at the light out-coupling surface 4 has a uniform brightness and/or intensity over the light out-coupling surface 4. Due to light losses in the light guide 2 and due to the light being out- coupled when it impinges on the light scattering and/or reflecting particles 5, the amount of light that reaches a position or location in the light guide 2 is dependent on the distance of that position or location from the light in-coupling surface 3. The more distant the position or location is from the light in-coupling surface 3 the less light reaches the position or location. By increasing the concentration of light scattering and/or reflecting particles 5 in regions 7 that are more distant from the light in-coupling surface, as in Figure 1, a higher proportion of light is out-coupled from that region per unit volume of the region, compensating for the light losses that have occurred before the light reaches that region. Thus, by adapting the concentration of embedded light scattering and/or reflecting particles 5 with regard to the distance from the light in-coupling surface 3, the light output over the light out-coupling surface 4 can be arranged to be uniform.

Figure 2 shows an illumination device 1 comprising a plurality of light emitting elements 10 and a light guide 2 comprising embedded light scattering and/or emitting particles 5, as described in relation to Figure 1. The light guide 2 shown in Figure 2 comprises three regions 6, 7, 8, of which region 7 comprises a different concentration of light scattering and/or reflecting particles 5 than the concentration of light scattering and/or reflecting particles 5 in regions 6 and 8. The concentration of light scattering and/or reflecting particles 5 in regions 6 and 8 is substantially zero, while the concentration of light scattering and/or reflecting particles 5 in region 7 is larger than zero. That is, regions 6 and 8 are substantially void of light scattering and/or reflecting particles, while region 7 comprises light scattering and/or reflecting particles 5 of a concentration enabling out-coupling of light that is visible to a viewer through or via the light out-coupling surface 4. No light is coupled out through or via the light out-coupling surface 4 of the regions 6, 8, that are substantially void of light scattering and/or reflecting particles. Light is however coupled out through or via the light out-coupling surface 4 of the region 7 comprising light scattering and/or reflecting particles. Some parts of the light guide 2 will therefore be transparent, while other parts will be illuminating. This results in a surprising effect that can be used to arrange illumination devices 1 with different aesthetic effects.

Figure 3A shows a similar illumination device 1 with one region 6 that is substantially void of light scattering and/or reflecting particles, and another region 7 comprising light scattering and/or reflecting particles of a concentration enabling out- coupling of visible light through or via the light out-coupling surface 4. Region 7 is smaller than region 7 of the illumination device 1 described with reference to Figure 2 and is not in contact with any of the edge surfaces of the light guide 2.

Another example is shown in Figure 3B, in which region 7 is star shaped and placed at the center of the light out-coupling surface 4. Region 6 and region 7 comprise embedded light scattering and/or reflecting particles. The concentration of light scattering and/or reflecting particles is higher in region 7 than in region 6.

Figure 4A schematically depicts a cross-sectional side view of an illumination device 1 comprising a light emitting element 10 and a light guide 2. The light guide 2 comprises two light guide members 2a, 2b. The cross sections of each of the light guide members 2a, 2b are wedge shaped or triangular. The light guide members 2a, 2b are joined such that the cross section of the light guide 2 is rectangular. In the shown example light guide member 2a comprises light scattering and/or reflecting particles 5 of a concentration that is larger than zero, while light guide member 2b is substantially void of light scattering and/or reflecting particles 5. As the light 11 enters the light in-coupling surface 3 of the light guide 2 and travels or propagates into the light guide 2 it encounters more and more light scattering and/or reflecting particles 5. That is, close to the light in-coupling surface 3 the light encounters few scattering and/or reflecting particles 5, and more distant from the light in-coupling surface 3 the light encounters a higher number of light scattering and/or reflecting particles 5. In this way light losses in the light guide 2 are continuously compensated for, such that the light that is out-coupled through or via the light out-coupling surface 4 is uniform over the light out-coupling surface 4.

Fig. 4B shows a cross-sectional side view of an illumination device 1 with a similarly arranged light guide 2, with different cross-sections of the light guide members 2a, 2b as compared to the light guide members 2a, 2b of the illumination device described with reference to Figure 4A. As illustrated in Fig. 4B, the cross sections of the light guide members 2a, 2b are "exponentially shaped" so as to have curved portions. In other embodiments other cross-sectional shapes of the light guide members are also conceivable. Figure 5 schematically depicts an illumination device 1, comprising a plurality of light emitting elements 10 and a light guide 2 comprising embedded light scattering and/or emitting particles 5. The light emitting elements 10 and the light guide 2 are arranged as in the illumination device 1 described above with reference to Figure 1. The concentration of embedded light scattering and/or reflecting particles 5 is uniform over the light guide 2 shown in Figure 5. The light guide 2 additionally comprises a plurality of light out-coupling structures 9 arranged on the light out-coupling surface 4. The light out-coupling structures 9 are adapted to out-couple light impinging on them from the light guide 2. The light out- coupling structures 9 may for instance be constituted by or comprise paint dots and/or scratches on the light out-coupling surface 4. In the embodiment shown in Figure 5 the light out-coupling structures 9 are distributed over the light out-coupling surface 4, such that the number of light out-coupling structures 9 per unit area of the light out-coupling surface 4 is different for regions 6, 7, 8 of the light out-coupling surface 4.

In Figure 5 region 7 comprises a higher number of light out-coupling structures 9 per unit area of the light out-coupling surface than regions 6 and 8 and therefore light is out-coupled at a higher degree at region 7, per unit volume of region 7, than at regions 6 and 8, per unit volume of the respective regions 6 and 8. That is, a higher proportion of the light reaching region 7 is out-coupled from the light guide 2 from region 7, per unit volume of region 7, than the proportion of light reaching the regions 6 and 8 and there being out- coupled from the light guide 2, per unit volume of the respective regions 6 and 8. The effect of having different numbers of light out-coupling structures 9 per unit area in different regions 6, 7, 8 of the light guide 2 (as in Figure 5) thus corresponds to the effect of having different concentrations of light scattering and/or reflecting particles 5 in different regions of the light guide 2 (such as in Figure 1).

The quantity of light 12 that is out-coupled through or via the light out- coupling surface 4 can thus be arranged to be higher for the region 7, comprising a higher number of light out-coupling structures 9 per unit area of the light out-coupling surface 4, than for regions 6 and 8, comprising a lower number of light out-coupling structures 9 per unit area of the light out-coupling surface 4, such that the light out-coupled from region 7 has a higher brightness and/or intensity than the light out-coupled from regions 6 and 8.

Alternatively, the number of light out-coupling structures 9 per unit area of the light out-coupling surface 4 in each region 6, 7, 8 can be arranged such that the light 12 that is out-coupled at the light out-coupling surface 4 has a uniform brightness and/or intensity over the light out-coupling surface 4. By increasing the number of light out-coupling structures 9 per unit area at regions 7 that are more distant from the light in-coupling surface, as in Figure 5, a higher proportion of light is out-coupled at that region 7, compensating for the light losses that have occurred before the light reaches that region 7. Thus, by adapting the number of light out-coupling structures 9 per unit area of the light out-coupling surface, with regard to the distance from the light in-coupling surface 3, the light output over the light out-coupling surface 4 can be arranged to be uniform. The embodiment described with reference to Figure 5 has an advantage over solutions where only light out-coupling structures arranged on the light guide are used to achieve a uniform light output from the light guide. The advantage of the combination of light scattering particles that are embedded in the light guide, and light out-coupling structures that are arranged on the surface of the light guide, is that fewer light out-coupling structures are required, while at the same time compensating for the limitations of having embedded light scattering particles for achieving a uniform light output from the light guide. The light out-coupling structures are in general visible to a viewer and it is therefore preferred to have as few of them as possible.

Figure 6A and 6B show illumination devices 1 arranged according to the same principles as the illumination device shown in Figure 5. The number of light out-coupling structures 9 per unit area of the light out-coupling surface 4 in region 6 is substantially zero, while the number of light out-coupling structures 9 per unit area of the light out-coupling surface 4 in region 7 is larger than zero. That is, region 6 is substantially void of light out- coupling structures 9, while region 7 comprises light out-coupling structures 9 of a number per unit area of the light out-coupling surface 4 that enables increased out-coupling of light through or via the light out-coupling surface 4. A small amount of light is coupled out through or via the light out-coupling surface 4 at region 6, which comprises light scattering and/or reflecting particles 5 but is substantially void of light out-coupling structures 9 on the light out-coupling surface 4. A comparatively larger amount of light is coupled out through or via the light out-coupling surface 4 at region 7, comprising light scattering and/or reflecting particles 5 and also light out-coupling structures 9 on the light out-coupling surface 4. Some parts of the light guide 2 will therefore illuminate light of a low brightness and/or intensity, while other parts will illuminate light of higher brightness and/or intensity. This results in an effect that can be used to arrange illumination devices 1 with different aesthetic effects, such as the square pattern shown in Figure 6 A, or to highlight a certain region, such as a logo, as shown in Figure 6B.

Figure 7 shows an example of an illumination device 1 in which the intensity of the light emitted by the light emitting elements 10 as well as the number of light out- coupling structures are adapted in order to achieve uniform brightness and/or intensity over a light out-coupling surface 4 of a triangular light guide 2. In order to achieve uniform illumination, the light emitting element 10a, providing light to the most narrow portion of the triangular light guide 2, is arranged to emit light of a low intensity, while the light emitting elements 10b, 10c, lOd and lOe, each providing light to increasingly wider portions of the triangular light guide 2, are arranged to emit light of increasingly higher intensity, respectively. In order to compensate for the differences in intensity of the light that is in- coupled at the different portions of the light in-coupling surface 3 of the light guide 2, light out-coupling structures 9 are arranged on the light out-coupling surface 4 of the light guide 2. A higher number of light out-coupling structures 9 per unit area of the light out-coupling surface 4 is arranged at the narrow portion of the triangular light guide 2, while decreasing numbers of light out-coupling structures 9 per unit area of the light out-coupling surface 4 are arranged at portions of the triangular light guide 2 that are increasingly wider.

In conclusion, a light guide is disclosed. At least a portion of the light guide comprises embedded light scattering and/or reflecting particles. The light guide comprises a light in-coupling surface adapted to couple light impinging on the light in-coupling surface into the light guide, a light out-coupling surface adapted to couple light out of the light guide, and a first region and at least a second region, each of the first and second regions comprising a portion of the light out-coupling surface. The light guide is arranged such that the proportion of light being coupled out from the first region of light travelling into the first region, per unit volume of the first region, is different from the proportion of light being coupled out from the second region of light travelling into the second region, per unit volume of the second region. The degree of light that is out-coupled from the light guide at selected positions can be adapted as desired, for example to give uniform lighting or to create an aesthetic effect. An illumination device comprising the light guide and a luminaire comprising the illumination device are also disclosed.

While the present invention has been illustrated and described in detail in the appended drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplifying and not restrictive; the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. 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. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A light guide (2) of which at least a portion comprises embedded light scattering and/or light reflecting particles (5), the light guide further comprising:

a light in-coupling surface (3) adapted to couple light impinging on the light in-coupling surface into the light guide,

- a light out-coupling surface (4) adapted to couple light out of the light guide, a first region (6) for coupling out a first proportion of light travelling within the first region, per unit volume of the first region, and

a second region (7) for coupling out a second proportion of light travelling within the second region, per unit volume of the second region,

wherein the first proportion of light is different from the second proportion of light.

2. A light guide according to claim 1, wherein the first region has a first concentration of embedded light scattering and/or light reflecting particles, and wherein the second region has a second concentration of embedded light scattering and/or light reflecting particles, the first and second concentrations being different and at least one of the first and second concentrations being larger than zero.

3. A light guide according to claim 2, wherein one of the first concentration of light scattering and/or light reflecting particles and the second concentration of light scattering and/or light reflecting particles is zero.

4. A light guide according to claim 2 or 3, wherein the first region is closer to the light in-coupling surface than the second region and wherein the first concentration of embedded light scattering and/or light reflecting particles is smaller than the second concentration of embedded light scattering and/or light reflecting particles.

5. A light guide according to any one of claims 2 to 4, wherein the concentration of embedded light scattering and/or light reflecting particles at least partly depends on the distance from the light in-coupling surface in at least a portion of the light guide.

6. A light guide according to any one of claims 2 to 5, wherein the concentration of embedded light scattering and/or light reflecting particles in the first region and the second region, respectively, at least partly depend on the distance of the first region and the second region, respectively, from the light in-coupling surface.

7. A light guide according to any one of claims 1 to 6, further comprising a plurality of light out-coupling structures (9) arranged on the light out-coupling surface, wherein the number of light out-coupling structures per unit area of the light out-coupling surface of the first region is different from the number of light out-coupling structures per unit area of the light out-coupling surface of the second region, and

wherein at least one of the number of light out-coupling structures per unit area of the light out-coupling surface of the first region and the number of light out-coupling structures per unit area of the light out-coupling surface of the second region is larger than zero.

8. A light guide according to claim 7, wherein one of the number of light out- coupling structures per unit area of the light out-coupling surface of the first region and the number of light out-coupling structures per unit area of the light out-coupling surface of the second region is zero.

9. A light guide according to claim 7 or 8, wherein the first region is closer to the light in-coupling surface than the second region and wherein the light guide is arranged such that the number of light out-coupling structures per unit area of the light out-coupling surface of the first region is smaller than the number of light out-coupling structures per unit area of the light out-coupling surface of the second region.

10. A light guide according to any one of claims 7 to 9, wherein the number of light out-coupling structures per unit area of the light out-coupling surface at least partly depends on the distance from the light in-coupling surface for at least a portion of the light out-coupling surface.

11. A light guide according to any one of claims 7 to 10, wherein the number of light out-coupling structures per unit area of the light out-coupling surface of the first region and the number of light out-coupling structures per unit area of the light out-coupling surface of the second region, respectively, at least partly depend on the distance of the first region and the second region, respectively, from the light in-coupling surface.

12. A light guide according to any one of claims 1 to 11, wherein the first region and the second region are arranged relative to each other such that at least some of the light coupled into the light guide travels to the second region via the first region, or vice versa.

13. A light guide according to any one of claims 1 to 12, wherein the light guide comprises a light guide member comprising the first region and the second region.

14. A light guide according to any one of claims 1 to 12, wherein the light guide comprises a first light guide member (2a) and a second light guide member (2b), the first light guide member comprising the first region and the second light guide member comprising the second region, and wherein each of the light guide members is arranged to be in optical contact with at least one of the other light guide members.

15. An illumination device (1) comprising:

a light guide (2) according to any one of claims 1 to 14; and

a light emitting element (10),

wherein the light guide and the light emitting element are arranged such that in operation at least some light emitted by the light emitting element is coupled into the light guide via the light in-coupling surface (3).