WO2009087587A1

WO2009087587A1 - Lighting system

Info

Publication number: WO2009087587A1
Application number: PCT/IB2009/050019
Authority: WO
Inventors: Michel C. J. M. Vissenberg; Ramon P. Van Gorkom; Marcellinus P. C. M. Krijn; Tim Dekker
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-01-08
Filing date: 2009-01-06
Publication date: 2009-07-16
Also published as: TW200940871A

Abstract

The present invention relates to a lighting system (1), comprising a light guide (5) having a first and a second surface facing each other, wherein at least one of the surfaces is capable of providing light in a first direction (100, 200). The lighting system (1) further comprises means capable of providing light (20), wherein the means capable of providing light (20) is disposed at at least one of said surfaces, and means (30, 31, 32, 35, 36) for shaping light from the means capable of providing light, wherein the shaping means (30, 31, 32, 35, 36) is arranged to shape light in the first direction (100, 200).

Description

Lighting system

TECHNICAL FIELD

The present invention relates to a lighting system comprising a light guide having a first and a second surface, wherein at least one of said surfaces is capable of providing light in a first direction.

BACKGROUND OF THE INVENTION

In the field of lighting for interior and exterior use, there is an increasing need to integrate the lighting systems as unobtrusively as possible. This enables architects and interior designers to, by means of lighting, create a style that clearly distinguishes one building from another or one room from another. The commonly used fluorescent lamp fixtures usually have a thickness of about 5 cm. It is, however, expected that these fluorescent lamp fixtures will be replaced by LED-based luminaires within 3-5 years.

In office environments, it is often desired to provide direct lighting for workspaces and indirect lighting for providing general lighting. Light fixtures with indirect and direct lighting have been introduced in order to provide lighting conditions that are considered to improve productivity and occupant satisfaction. Even though these parameters are hard to quantify, the benefits are said to be significant. Moreover, for fulfilling the requirements for office lighting, collimation angles of typically 2x45° are required. Collimation of the light reduces glare. In addition, to reduce glare, the luminance for angles above 65° should be below 1000 cd/m².

In order to meet requirements for reduction of glare, the LED-based lighting systems are provided with optics using refraction and total internal reflection (TIR) for collimation of the light and/or reflecting (metal) collimators. This special optics is fitted closely to the LEDs, such that the size of the lighting system is kept at a minimum. Disadvantageously, this complicates construction of the lighting system and renders the lighting system less flexible in the use of various LED types. An optical system that collimates the light far away from the light sources is more flexible in the use of different LED types. However, due to the distance between the lighting system and the optical system, the light is spread out. Spread light usually requires larger (thicker) collimators. As a consequence, a lighting system with a larger collimator may become obtrusive.

Hence, there is a need for unobtrusive lighting systems that are flexible in the use of different types of light sources.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved lighting system that alleviates the above-mentioned problems of prior art.

This object is met by the lighting system as set forth in the appended independent claim 1. Specific embodiments are defined in the dependent claims.

According to an aspect of the invention, there is provided a lighting system, comprising a light guide having a first and a second surface facing each other, wherein at least one of the surfaces is capable of providing light in a first direction. The lighting system further comprises means capable of providing light, wherein the means capable of providing light is disposed at at least one of said surfaces, and means for shaping light from the means capable of providing light, wherein the shaping means is arranged to shape light in the first direction.

An idea of the invention is to provide a lighting system that comprises a light guide, means for providing light and means for shaping light. Further, the light guide has a first and a second surface. The means for providing light is arranged in the vicinity of any one of the surfaces of the light guide. At least one of the surfaces is capable of providing light in a first direction. Light, which is provided by said means for providing light, is guided through the light guide such as to be shaped (or optionally collimated) by the shaping means. The shaping of the light may, preferably, involve controlling of the angle of the beams in the light emitted in the first direction. In this manner, the lighting system provides shaped light in the above-mentioned first direction.

In embodiments of the present invention, it is preferred that the means capable of providing light is associated with the shaping means. Most preferably, the means capable of providing light is aligned with the shaping means. Optionally, the light guide guides light from said means capable of providing light to said shaping means, thereby light may be emitted in the first direction after passing through or by the shaping means.

The means capable of providing light (or means for providing light) may, in embodiments of the lighting system according to the invention, be any one of dots of paint, dots comprising a phosphor-based material, diffusers, optical structures for refracting, diffracting and/or reflecting light, LEDs or organic LEDs or a combination thereof. For example, any one of the following diffusers may be used: ground glass diffusers, teflon diffusers, diffusers based on TiO2, MgO, Ta2O5, AL2O5 particles, holographic diffusers (isotropic diffusers or anisotropic diffusers), opal diffusers, grayed glass diffusers or a combination thereof. The means for providing light may be seen as a light out-coupling element, a scattering dot or a diffusively scattering dot. In some cases, as for example when the means capable of providing light comprises an LED, the light out-coupling element generates light. The means capable of providing light may, preferably, be disposed at any one of the surface. It is preferred to arrange the means for providing light in optical contact with the light guide. The means for providing light is intended to couple the light out of the light guide and may be in the form of out-coupling elements, or scattering dots. When light is coupled out of the light guide by the means for providing light, the angular distribution of the out-coupled light may be determined by the shaping means. For some applications, it may be preferred that the light from the means capable of providing light is diffusive, while for some other applications it may be desired that the light from the means capable of providing light is collimated.

In an embodiment of the lighting system according to the present invention, the means for providing light comprises a pixilated OLED. In this manner, light reflected at the first and/or second surface may be allowed to pass through the OLED at transparent portions between pixels before being emitted as, for example, indirect light.

In particular, for the case where the means capable of providing light comprises phosphor-based materials, it is common practice to use white LEDs consisting of blue-emitting dies that excite a yellowish phosphor. The combination of yellow light and the remainder of blue light renders white light. In a (remote) phosphor system, the phosphor is not applied directly onto the die. The advantages are more control over color (not all phosphor types can withstand high temperatures close to the die) and a higher efficiency (less light back to the die). Light from blue or near-UV LEDs may be coupled into the light guide. The phosphor is then located at the means capable of providing light (out-coupling dots). The dominant emission wavelength of a central part of means capable of providing light, provided with phosphor, may differ from a peripheral part of the means for providing light. As a result, an angular dependent appearance of the color may be obtained.

Further, in embodiments of the lighting system according to the present invention, the first direction may be in a direction such that light emitted in the first direction may be used as direct light (i.e. the first direction is, for example, towards a desk or an object to be highlighted). Conversely, in other embodiments of the lighting system according to the present invention, the first direction may be in a direction such that light emitted in the first direction may be used as indirect light (i.e. the first direction is, for example, towards the ceiling or a reflective screen). In some embodiments of the lighting system according to the present invention, the first surface is capable of providing light is in the first direction and the second surface is capable of providing light in a second direction (the second direction being different from the first direction). Thereby, a lighting system providing both direct light and indirect light is provided. The direct light (or functional light) may be collimated for optimization for reading or alike. The indirect (or atmosphere) light may be directed towards the ceiling for providing background lighting. On the other hand, the direct light may be used to highlight elements in the interior in order to create a certain atmosphere, while the indirect light may provide a functional background light level.

In yet further embodiments of the present invention, there is provided a diffuser foil for directing the light back into the light guide at the second surface. It is preferred that the diffuser foil is not in optical contact with the light guide. Accordingly, the amount of light in the first direction is increased.

In an embodiment of the lighting system according to the invention, the means capable of providing light is arranged at the second surface and the shaping means comprises a mask with at least one opening for shaping of light emitted in the first direction. The mask is, preferably, disposed at the first surface. Advantageously, the light from the means for providing light is shaped according to the size and shape of the opening in the mask, i.e. light from the means for providing light that is incident on the mask (not at the opening) will be cut-off and, hence, not emitted in the first direction. The opening may be arranged to match the means for providing light. Further, the mask may be diffusely reflective in order to direct light incident on the mask (not the opening) in the second direction.

In other embodiments of the lighting system according to the present invention, the mask may comprise a retro -reflective mask. The retro-reflective surface is, preferably, directed towards the light guide. An ideal retro-reflector resends all light that does not pass through the opening in the mask back to the means for providing light. At the means for providing light, the light is scattered again and it may either pass the mask opening or be retro -reflected again, ad infinitum. Hence, all light is used as direct light with the desired angular width and cut-off. Further, the mask may contain phosphor in order to provide indirect light of a different color (e.g. more warm white for the indirect light in the second direction) than the direct light (in the first direction). Again, the phosphor material is, preferably, directed towards the light guide. In order to avoid an uncomfortably bright spot directly above the lighting system according to embodiments of the present invention, the indirect light distribution is, preferably, peaked at large angles with respect to a normal of the light guide. This may be obtained by using a mask with a specularly reflecting surface, facing the light guide, instead of a mask with a diffusive reflecting surface. In embodiments of the lighting system according to the invention, the shaping means comprises a mirror, disposed at the opposite surface compared to the surface at which the means for providing light is disposed. The shape of the mirror may be circular, but other shapes are also possible. In a case, in which the mirror is circular, the diameter of the mirror affects the ratio of light emitted in the first and the second direction. Preferably, the mirrors should not be in optical contact with the light-guide in order to benefit as much as possible from the principle of total-internal reflection (TIR).

In other embodiments of the lighting system according to the invention, the shaping means comprises a mirror, disposed at the surface at which the means for providing light is disposed. Expressed differently, in embodiments of the lighting system the mask comprises a mirror. The mirror may, hence, be in the form of a mask with holes for light, which is to be emitted in the first direction. The shape of the holes in the mirror may be circular, but other shapes are also possible. If the holes are non-circular, the cut-off angle may be dependent on the angular direction. In this manner, some rays (or beams) at certain angles are redirected to be emitted at the second surface, i.e. coupled out of the light guide at the surface at the opposite side of the light guide compared to where the mirror is arranged.

In embodiments of the lighting system, the mirrors or the mask openings (holes) are arranged in a hexagonal manner.

In still further embodiments of the present lighting system, the means capable of providing light is arranged at the first surface and the shaping means comprises a lens arrangement (or a lens) for shaping light emitted in the first direction. The lens may have a first strength (refraction/reflection ability) within a radius of the lens (a first region) and a second strength out-side mentioned radius of the lens (a second region). It is also possible to provide a lens with more than two different regions with different strength. It is to be noted that strength of the lens may be radius dependent and increases for increasing radii. Preferably, the lens comprises a transmissive lens and is arranged at the first surface. For example, a Fresnel type lens, which has been modified according to the above may be used. The first, inner region may function as a Fresnel lens, whereas the second, outer region may be modified and rely on TIR (see examples below). Further, the lens may comprise a reflective lens. In case of a reflective lens, or lens arrangement, the lens may be located at the opposite surface of the light guide compared to the surface where the means for providing light is arranged (generally, at the second surface of the light guide). Also in the case of a reflective lens, the lens may be of Fresnel- type according to the above. Beam shaping may be accomplished in several ways. For example, by replacing round lenses with astigmatic lenses the beam may acquire a different shape in different directions. An example of an astigmatic lens is a cylindrical lens with a lens action (e.g. refraction) in one direction only.

Explicitly, it is envisaged that the shaping means may comprise mirrors, lens arrangements, masks and/or a combination thereof.

In embodiments of the present lighting system, the means capable of providing light is shifted in relation to the means for shaping light for changing the direction of the light beam from the lighting system. In this manner, beam direction and beam focusing may be performed, more particularly the direction and/or focus of the light beam may be user- adjustable.

In a similar manner, the beam from a lighting system with a large area may be focused on a target area. This may be accomplished by shifting the means for providing light at the right side to the right with respect to the shaping means. Further, the means for providing light at the left side is shifted to the left. Thereby, the beams at the sides of the lighting system are directed inwards.

Further, in order to reduce the number of shadows obtained in the direct light, it may be possible to shift the means for providing light at the right side to the left with respect to the shaping means and the means for providing light at the left side to the right. Thereby, the beams at the sides of the lighting system are directed outwards and, thus, reducing the number of shadows as indicated above.

Moreover, the shape (symmetry) of the beam may be changed by varying the shape of the means for providing light and/or the shape of the shaping means, such as opening in a mask/mirror or shape of a lens. In accordance herewith, an elliptical shape of, for example, the opening in the mask generates a beam with an elliptical cross-section. The shape of the means for providing light and/or the shape of the shaping means (for instance, the openings in the mask) may be in the form of a circle, a polygon, a square or alike.

Furthermore, the beam width and cut-off are determined by the area (in the case of circular means for providing light; the diameter) of the means for providing light, the thickness of the light guide and the area (in the case of circular openings in the shaping means: radius) of the openings in the shaping means, e.g. a mask and/or a mirror. For example, when increasing the diameter of the means for providing light and decreasing the radius of the opening, the intensity of the resulting beam in the first direction is decreased. In further embodiments, the mask (or a mirror in the form of a mask) may comprise a specular reflector with at least one opening (hole). The reflective area is to be directed towards the light guide. Thereby, bright spots directly above the lighting system may be reduced. By choosing the ratio of specular versus diffuse reflection, the indirect light (indirect beam shape) in the second direction may be tuned to a desired appearance.

In an embodiment of the present lighting system, beam width, cut-off, beam shape, direction, focus and/or color may be adjusted dynamically. The adjustment may be performed by electrical and/or mechanical means. For example, two identical masks with circular holes may be shifted with respect to each other in order to form a mask with eye- shaped holes to produce an elliptical light beam. The electrical means may comprise switchable diffusers (e.g. LC gel or PDLC), switchable reflectors or electro-chromic layers. With patterned switchable diffusers as a mask, the size, shape and/or location of the mask holes may be adjusted dynamically and, hence, the beam width, cut-off and/or direction may be adjusted dynamically. By applying a switchable diffuser in combination with a specularly reflecting mask, the indirect light directions may be adjusted dynamically or the color effects may be adapted dynamically. Similar color effects can be obtained with switchable reflectors in combination with a static diffuser, or with electro -chromic materials.

Further, it is possible to cover the second surface of the light guide with a retro -reflecting layer (sheet). An ideal retro-reflecting, top sheet redirects light that hits the means for providing light in such a way that the shaping means is avoided. Thereby, the light is redirected back into the light guide again. Compared to the embodiment of the lighting system with a diffusive sheet at the second surface, this reduces the probability that light escapes from the light shaping means (i.e. the mask/mirror opening) at large angles.

The lighting system may also be switched to an "ambient light only" mode by closing the mask holes (either mechanically or electronically). Alternatively, the lighting system may be set in a "direct light only" mode by making the mask fully transparent or by redirecting all indirect light by a (switchable) diffusive top-sheet. In the "direct light only" mode, there will be a trade-off between light flux versus worsened beam profile and cut-off. The lighting system according to embodiments of the present invention may further comprise a primary light source and the means capable of providing light may comprise a secondary light source. The primary light source may comprise an LED, an organic LED, a fluorescent lamp or alike or a combination thereof.

In the lighting system according to embodiments of the invention, the light guide further has sides into which light may be fed into the light guide. Additionally or alternatively, light from side-emitting LEDs (primary light source) may be fed into the light guide via recesses distributed over the guide. In this manner, light is coupled into the light guide. Further, side-emitting optics may be integrated with the light guide for allowing the use of forward emitting LEDs as a primary light source. The light guide, which preferably is flat and/or thin, may be manufactured of, for example, polymethyl methacrylate (PMMA), poly-carbonate (PC), including a scratch-resistant layer, or glass, In embodiments of the present invention, the lighting system may comprise an array of means capable of providing light. The array may comprise light elements comprising means for providing light. The light elements may differ from each other according to embodiments described or in the disclosure of the present application.

Furthermore, the lighting system may comprise an array of means for shaping light. The array may comprise shaping elements comprising means for shaping light. The shaping elements may differ from each other according to embodiments described in the disclosure of the present application. For example, some shaping elements may comprise lens arrangements, while other shaping elements comprise mirrors, and further shaping elements may comprise mirrors and lenses, in one single embodiment of the lighting system according to the present invention. Furthermore, in other embodiments the shaping elements may comprise holes of different sizes and shapes as described above.

It is to be understood that the term "pitch" relates to the relative distance between elements in the arrays of light elements and shaping elements.

The size and/or shape of the means for providing light (for example, the scattering dots) and/or the pitch of the means for providing light may depend on its location, i.e. depend on the relative distance to the nearest LED. The further away, the larger the dots should be. In this manner, it may be compensated for decrease in intensity further away from an LED (a primary light source). However, in the present lighting system the size of the scattering dots and the pitch is strongly coupled to the beam profile via the size and spacing of the mask holes. Hence a uniform appearance in the lit state (with varying dot size or spacing) may result in a non-uniform appearance in off-state. Therefore, in an alternative embodiment of the invention it may be possible to use scattering dots of constant size and spacing, but with varying scattering strength depending on the relative distance to the nearest LED. Possible implementations of this alternative embodiment comprises e.g. the use of dithering dots (dots that consist of small scattering patches with tuneable density), variable thickness of white paint dots (to tune the transmission), and/or variable roughness of sandblasted surface dots. It should however be noted that the dots can have variable surface scattering roughness in general. Accordingly, such dots can for example be made by sandblasting but also by etching.

Furthermore, a continuous variation in beam direction is obtained by taking a pattern of means for providing light with a slightly larger pitch (in one or in both directions) than the shaping means, such as the mask-hole pitch. The other way around, the light beam may be formed to be more diverging by choosing a smaller pitch.

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 may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

Fig. 1 is a view in oblique projection over a flat lighting system according to an embodiment of the invention;

Fig. 2a-2c are views in different oblique projections over the lighting system in Fig. 1;

Fig. 3 is a cross-sectional view over a portion of the lighting system in Fig. 1.

Fig. 4a-4b are diagrams of a radial beam profile in a first and a second direction of light from a lighting system according to embodiments of the present invention; Fig. 5 is a further diagram of a radial beam profile of light from a lighting system according to another embodiment of the present invention;

Fig. 6 is still a further diagram of a radial beam profile of light from a lighting system according to a still further embodiment of the present invention; Fig. 7 is a view in oblique projection over another embodiment of the present lighting system;

Fig. 8 is another diagram of a radial beam profile of light from a lighting system according to another embodiment of the present invention;

Fig. 9 is yet another diagram of a radial beam profile of light from a lighting system according to yet another embodiment of the present invention;

Fig. 10 shows a cross-sectional view over a portion of a retro-reflector foil;

Fig. 11 is still another diagram of a radial beam profile of light from a lighting system according to still another embodiment of the present invention;

Fig. 12 is a top, plan view over a lighting system according to embodiments of the invention;

Fig. 13 is a cross-sectional view over a portion of a lighting system, using a lens for shaping of light, according to embodiments of the present invention;

Fig. 14 shows refraction at a first and a second location on the lens in Fig. 13 in a cross-sectional view; Fig. 15 shows refraction of another type at a location on the lens in Fig. 13 in a cross-sectional view;

Fig. 16 is a top, plan view over a portion of the lighting system according to Fig. 13;

Fig. 17 is a cross-sectional view over a portion of an exemplifying lighting system, using a reflective lens, according to another embodiment of the present invention;

Fig. 18a- 18c show different types of reflective lenses or lens arrangements;

Fig. 19a and 19b are polar diagrams of light emission from transmissive and reflective lenses, respectively;

Fig. 20 is a cross-sectional view over a portion of a lighting system, using lenses and mirrors, according an embodiment of the present invention;

Fig. 21 is a cross-sectional view over a portion of a lighting system, using mirrors disposed at the opposite surface of the light guide compared to the surface at which the means for providing light are disposed, according another embodiment of the present invention; Fig. 22 is a cross-sectional view over a portion of the lighting system in Fig. 21, further comprising a mirror in the form of a mask, disposed at the same surface as the means for providing light is disposed, according another embodiment of the present invention; and Fig. 23a-23d shows different implementations of scattering dots having variable out-coupling efficiency.

DETAILED DESCRIPTION

Throughout the following description, the same or similar reference numerals have been used to denote the same or similar elements and/or features of the lighting system according to embodiments of the present invention.

Fig. 1 shows a thin lighting system 1 comprising a light guide 5 with a dot pattern of light out-coupling elements 20 (or means for providing light) on one side of the guide. Light is coupled in at the sides of the guide 5, or via recesses distributed over the guide 5. When light is coupled out by a light out-coupling element 20 (which also will be referred to as a scattering dot or a diffusively scattering dot), the angular distribution of the out-coupled light is trimmed by a flat mask (or shaping means) at the opposite side of the guide 5. The mask 30 has a hole pattern 31 that matches the pattern of scattering dots 20 and is (diffusely) reflective in order to send the trimmed light upwards to the ceiling. The light emitted upward may be used as indirect light. In this example, the first direction is indicated by the reference numeral 200, whereas the reference numeral 100 denotes a second direction in which light is diffusely emitted in order to provide indirect lighting. In other examples of the lighting system 1, the first direction may be in the direction indicated by reference numeral 100 and, consequently, the second direction may be in the direction indicated by reference numeral 200.

The principle of collimating light by masking is illustrated in Fig. 2a-2c. In Fig. 2a, it is illustrated that the whole scattering dot is visible at small angles from a normal to a surface of the mask. At medium angles from the normal of the mask, as seen in Fig. 2b, a portion of the scattering dots (out coupling areas/elements) is visible. There is illustrated, in Fig. 2c, that the scattering dots are completely cut-off by the mask at larger angles.

Referring to Fig. 3, the lighting system 1 comprises a PMMA light guide 5 with a thickness of H = 4 mm and a refractive index n=1.49. The light is generated by a square array of side-emitting LEDs that couple light into the guide via holes in the guide at a pitch of 4 cm (not shown). For reasons of glare, a cut-off angle of 60° α_c in air is required. That implies αi = 35° (cut-off in the light guide). The angle α₂ = 42° (TIR angle in PMMA). With a dot diameter of D = 1.5 mm, a dot pitch P = H (tg αi + tg (X₂)=6.4 mm and a radius of the holes in the mask R = H tg αi -D/2 = 2.1 mm is calculated. Ray-tracing simulations with ASAP software have been performed. These simulations indicate that 33% of the light flux may be used for direct (or task) lighting, 41% flux is indirect light to the ceiling, and the rest is lost (15% absorbed by LED array (with reflectivity R=0.5), 10% absorbed by out-coupling dots (or scattering dots, R=0.97), and 1% absorbed by diffuser (R=0.97)).

The radial beam profile of the indirect light and the direct light is shown in Fig. 4a and 4b, respectively. In the diagrams the radial intensity (RI), as a percentage (%) of a peak intensity, is plotted against sin of the angle from a normal to the light guide (the jagged graphs in Fig. 4a and 4b). The smooth graphs (starting at zero for sin θ equals zero in these examples) show the integrated beam profile, integration starting at the center of the beam. In the following examples, involving graphs of radial beam profiles, the jagged graphs are, likewise, related to the beam profile as explained above and the smooth graphs are, similarly, related to the integrated beam profile. The indirect light is diffuse light and the direct light has a specific beam profile. Furthermore, the indirect light beam has a Lambertian distribution, which is determined by the scattering properties of the diffuser (or the mask), whereas the direct light beam is collimated to a width of about 2 x 45 degrees and has a cutoff at about 60 degrees. In some cases, there may be provided a separate diffuser with holes centered at the same locations as the holes in the mask.

In other examples of the lighting system according to the present invention, the indirect light may be shaped. For example, in order to avoid an uncomfortably bright spot directly above the lighting system, the indirect light distribution is preferably peaked at large angles with respect to a normal of the light guide. This is obtained by using a specular reflector (with holes) instead of a diffusive reflector. The indirect light beam profile, obtained via specular reflection, is plotted in Fig. 5. The diagram in Fig. 5 is similar to the diagrams in Fig. 4a and 4b. The indirect beam shape may be tuned by selecting the ratio of specular reflection versus diffuse reflection. Consequently, a more even brightness of the indirect light (distributed on the ceiling) is achieved, since the light beam is directed in a direction towards being parallel with the ceiling.

As explained above, the beam width and cut-off are determined by the dot diameter, the thickness of the light guide, and the radius of the holes in the mask. For example, a more narrow beam with the same-cut-off may be obtained by choosing a larger out-coupling dot size D=2.0 mm in combination with a smaller hole radius, R = 1.8 mm. The resulting beam profile is given in Fig. 6. The beam width is reduced to about 2 x 35 degrees, while the cut-off is maintained at 60 degrees. As may be seen from the plotted graph in Fig. 6, the beam intensity drops at smaller angles than in Fig. 4a and 4b. Since the beam profile in Fig. 6 is narrower (i.e. better "tuned"), the ratio of direct to indirect light is decreased. In this example, the direct light is 29% and the indirect light is 49%.

Furthermore, the beam width and cut-off, the shape (symmetry) of the beam may be changed by varying the shape of the holes in the mask. An example of an elliptical spot shape is given in Fig. 7. Additionally or alternatively, the shape of the light out-coupling dot may be changed in order to provide a different beam width, cut-off angle and or shape of the beam.

In the following, four different examples on how to alter the ratio of direct light to indirect light may be achieved.

A straight forward way to achieve more direct light is to redirect the indirect light back to the mask (the shaping means) by a diffuser foil on top of the light guide. The diffuser foil is, preferably, not in optical contact with the guide. In the lighting system described above, an enhancement of the direct light from 33% to 66% of the total flux is attained. As shown in Fig. 8, there is some beam formation, but the cut-off is not as distinct or even non-existent. The direct light beam is collimated to a width of about 2 x 50 degrees, but there is no cut-off at large angles. A further way to enhance the direct light flux is to use a retro -reflective mask

(instead of a diffuser or specular reflector). An ideal retro-reflector resends all light that does not pass the mask holes back to the out-coupling dot. At the dot, the light is scattered again and it may either pass the mask hole or be retro -reflected again, ad infinitum. Hence, all light is used as direct light, which will have the correct angular width and cut-off. With a non-ideal retro -reflector (that introduces some angular spread), part of the light will miss the out- coupling dot and will exit the system as indirect light.

As an example, there has been modeled an engineering-grade retro -reflector that consists of very small glass beads (n=1.9) embedded in a reflecting substrate. The retro- reflector is illustrated in Fig. 10. The spheres have a refracting index of n=1.9. The top half of the spheres are coated with a reflector material M. The reflective index of the reflector material is R = 0.95.

Thanks to the geometry of the proposed retro-reflector, about 1/3 of the retro- reflected light is redirected to the out-coupling dot. This is to be compared with about 15% for the case with a lighting system having a diffuser as described above. There has been a modest increase in direct light to 37%, and a decrease in indirect light to 29%. The beam shape and cut-off are conserved, as shown in Fig. 9. Consequently, it may be concluded that the quality of the retro-reflecting sheet determines to a high degree the efficiency of the retro- reflector. Another way to enhance the direct light flux is to cover the top side of the light guide by a retro -reflecting sheet, or to make both the mask and the top sheet of a retro- reflecting material. As above, an ideal retro -reflecting top sheet redirects all indirect light that does not hit the out-coupling dot in such a way that the mask holes are avoided. In comparison with using a diffusive top sheet, the probability that light leaves the mask holes at large angles is reduced. For a case with two retro -reflecting foils (both mask and top sheet) an analysis has been performed. The analysis showed an increase in direct light to 49%. The resulting beam profile is shown in Fig. 11. It shall be noted that the cut-off is better than in Fig. 8 (diffusive mask and diffusive top sheet), but not as distinct as in Fig. 9 (retro -reflecting mask, no top sheet). In this case, the quality of the retro -reflecting foil strongly determines not only the efficiency (which is not very high in this example), but also the beam quality (cut-off).

A still further way to enhance the direct light is to structure the light out- coupling dots. So far, a Lambertian scattering pattern has been assumed. The scattering profile may also be tuned to produce a peak in the perpendicular direction, thereby enhancing the direct light flux through the mask holes. For example, the scattering dots may be made of a holographic diffuser with a well-defined scatter pattern. Alternatively or additionally, micro-structures may be used. A micro -structure may contain a number of facets at about 45 degrees to the plane of the light guide. Such a micro -structure may be used in combination with a light source (primary light source) that emits light that is collimated in the plane of the light guide.

Yet another way to enhance the direct light is to place the LEDs directly in front of the mask holes, at the positions of the scattering dots. A downward beam of direct light may be enhanced by collimating and aiming the light beams from the LEDs in the direction of the mask hole. Since this allows for a direct view into the LED more care may be needed to avoid glare. For example, the LEDs may produce a more narrow beam

(comparable to a light beam from a spot light), while other light sources produce a broader (general illumination-like) beam via the scattering dots.

In further examples of the lighting system, beam direction and beam focusing may be performed by shifting the mask (or more generally, the shaping means) with respect to the dot pattern. In this manner, a lighting system with an asymmetric beam direction may be attained. An example is shown in Fig. 12. An asymmetric light beam from the out- coupling dots in Fig. 12 is generated by using a mask that is shifted with respect to the out- coupling dots. In a similar manner, the beam from a large-area lighting system may be focused on a target area (e.g. a desk). This may be accomplished by shifting the out-coupling dots at the right side to the right with respect to the mask holes. Further, the dots at the left side are shifted to the left. Thereby, the sides of the light beam are directed inwards.

A continuous variation in beam direction is obtained by creating a dot pattern with a slightly larger pitch (in one or in both directions) than the mask-hole pitch. The other way around, the light beam may be formed to be more diverging by choosing a smaller dot pitch.

In further examples of the lighting system, the out-coupling dots may comprise a yellowish phosphor material. In this case, it is preferred to pump the light guide with blue LEDs. Furthermore, the mask may contain (a different) phosphor in order to provide indirect light of a different color (e.g. warmer white light) than the direct light. The direct light may also contain color effects by using different (color) phosphor dots for different mask-holes. The different areas in the spot (e.g. centre vs. periphery, or left vs. right side) can, in this manner, be given different colors. For example, a white center spot with a colored halo around it, or a color gradient from left to right may be provided.

In other examples of the lighting system according to the invention, the color of the indirect light may be acquired by using a colored mask, i.e. by using paint. The mask may have a pattern of colors for creation of a color effect on the ceiling. For example, the mask may contain diffusive patches of a different color than the sheets, which are processed to provide specular reflection. As a result, there is obtained an indirect light pattern on the ceiling with a different color (by means of the diffuser) just above the luminaire than far away from the luminaire (generated by the specular reflector).

With reference to Fig. 13, there is shown another example of the lighting system according to the present invention. There is shown a lighting system based on a thin light guide 5 with a pattern of out-coupling structures 20 (or 'dots'). Light is coupled in at the sides of the light guide or via recesses distributed over the guide into which light from side- emitting LEDs is coupled. Light is coupled out from the light guide at the side where the dot pattern 20 is located. Light rays will travel inside the light guide by means of total internal reflection (TIR) until they encounter a scattering dot. The scattering dots are an essential part of the out-coupling structure. They, for example, consist of diffusely reflecting dots 20, such as dots of white paint; each dot will diffusely reflect (scatter) the light, thereby acting as a secondary light source. The dots 20 hardly transmit any light. Some of the light scattered by the dots 20 will still be trapped inside the light guide by means of TIR (i.e. light scattered at angles exceeding the critical angle θ for TIR). Light scattered at angles not exceeding the critical angle will be able to leave the light guide at the side opposite to where the dot pattern is located (top side in Fig. 13). This is the case for rays that obey θ < θ_c, with θ_c = asin(l/n), where θ_c is the critical angle and n is the index of refraction of the light guide 5. The light is reflected back by a flat mirror 33 (e.g. a sheet of ESR foil produced by the company 3M). Next, the reflected light will be coupled out of the light guide 5 at the side where the dots 20 are located (bottom side in Fig. 13). A Fresnel-type 'lens' 32 is used as a beam-shaper to redirect the out-coupled light rays in order to collimate these rays. The diameter db of the beam of light (not shown in Fig. 13) coupled out and redirected by the 'lens' fulfils the relation:

Here, t denotes the thickness of the light guide. Preferably, the lens-diameter exceeds the beam diameter: di > db. Preferably, but not necessary, also the dot pitch p (which is equal to the lens pitch) exceeds the lens diameter di. Preferably, the dot diameter is less than the thickness of the light guide: da < t.

In practice, the choice of the actual dot size and dot pitch relative to the thickness of the light guide is determined by the following two considerations.

Firstly, the larger the dot size or dot pitch, the more light will be coupled out and the shorter the actual range on average traveled by a ray after being injected by an LED will be. In order to provide a lighting system that is robust with respect to failure of one or a few LEDs, it is preferred to arrange the dots and the lenses such that a ray on average travels a distance that is at least of the same order of magnitude as the spacing between the LEDs.

Secondly, the larger the dot size, in relation to the thickness of the light guide, the more difficult it is to obtain a collimated beam from the entire lighting system.

Preferably, the focal distance of the lenses is close to f = 2t/n. This corresponds to a more or less parallel beam of light from the lens.

There are two issues that have to be solved in order to make the lens useful in practice. The first issue is the following: Consider as an example t = 1.25 mm, n = 1.49 (which is true for a light guide of PMMA). Then, di ~ db = 4.5 mm and f = 1.7 mm. This implies that the lens diameter is considerably larger than the preferred focal length. In other words, the lens is strong. In fact, a Fresnel-type lens may be made (very) strong, while still remaining relatively thin. Notably, the lens will deviate from a standard Fresnel lens. The reason for this will be explained with reference to Fig. 14 and Fig. 15 in the following paragraphs.

Consider the ray A in Fig. 14. The ray A, which is located close to the optical axis of the lens, will be easy to refract. This is not true for another ray B. The ray B is far from the optical axis. For a common round lens, the angle with respect to the surface of the lens would be large. Due to the large angle, there is a great probability that the lens, instead of refracting the ray B, reflects the ray B.

This problem may be solved by modifying a standard Fresnel-type lens such that the refraction relies on TIR beyond a certain radius from the optical axis of the lens 32. In Fig. 14, there is demonstrated a ray B, which is incident on a lens. At the location of the ray B and towards the periphery of the lens 32, the lens has been modified. Instead of using the principle of refraction, the deflection of the ray B is governed by the principle of TIR. In other words, the inner region of the lens behaves like an ordinary Fresnel lens. The outer region is modified and relies on TIR. The second issue is the following: By approximation, the lens should make an image of the scattering dot 20 in Figs. 14 and 15. However, due to the fact that the index of refraction n of the light guide 5 exceeds that of air, refraction of a ray occurs at the side where the dots are located at a distance approximately equal to the distance R at which the ray traverses the lens. The virtual location above the lens where the ray seems to originate from depends on this distance R. This implies that the lens strength should depend on the distance R at which a ray traverses the lens. The larger R, the stronger the lens has to be. It may be shown that by approximation the lens strength should obey the following relation:

s(R) = ^ f(R) = - Z ₀ + ¹ Z₁ , with z_o = R/tan(asin(n-sin(atan(R/2t)))) .

In this relation, zo and zi are the object distance (the optical distance from a scattering dot to the lens) and image distance, respectively. For a parallel beam, zi is infinite and f = 2t/n for small values of R (i.e. close to the optical axis of the lens). For a diverging beam zi < 0. In other words, the lens strength is not a constant as for ordinary lenses or Fresnel-type lenses, instead it is dependent on the radius and increases for increasing radii. In Fig. 16, there is shown a bottom view of the layout according to Fig. 13. The dots 20 and lenses 32 are arranged in a hexagonal pattern at the same surface of the light guide 5. In this example, the center of the scattering dots and the lenses are aligned. For other examples of the lighting system according to embodiments of the invention, the center of the scattering dots and the lenses may be arranged such that they are not aligned with each other. Now referring to Fig. 17, there is shown a reflective lens for use as a shaping means. The reflective lens has a diameter d_r. The lens strength of the reflective lens is not constant as for an ordinary lens. It has been observed that, in general, it is easier to manufacture lenses based on reflectivity than lenses based on refraction. In addition, the behavior of a reflective lens is more predictable, from an optical point of view, than behavior of refractive lenses. In Figure 18a - 18c, there is illustrated some reflector shapes. Fig. 18a shows a the Fresnel-type reflector, which is more compact compared to the lens shown in Fig. 17. The polygon shaped reflector (Figure 18b) enables tuning of the beam spread. Thereby, improvement of the mixing and uniformity of the rays within the beam is obtained. Moreover, the reflector may be made slightly diffusive, e.g. by roughening its surface. As a result, similar improvement of mixing and uniformity of the rays within the beam may be obtained. There is shown a perforated reflector in Fig. 18c. In this manner, a combination of functional light emitted downwards and indirect (atmosphere) lighting, i.e. illumination of the ceiling, emitted upwards is achieved. Further, examples of reflector shapes may be obtain by combining the reflector shapes shown in Fig. 18a -18c. Two ray-tracing simulations (with ASAP software package) for measuring the optical quality and efficiency of a proposed lighting system have been performed. In the ray- tracing simulations, the following values of system parameters were used: t=1.25 mm, n=1.49, P=6.0 mm, da = 1.0 mm, di = d_r = P. In Fig. 13 and 15, the meaning of the reference characters are indicated. In the simulations, the radii of curvature for the transmissive and reflective lenses were set to 5.5 mm.

The first simulation, the result of which is shown in Fig. 19a, is based on the use of transmissive, spherical lenses (plano-convex). Although such lenses are not optimal for this task, the results show that it is possible to obtain reasonably good results, i.e. the resulting lighting system does not suffer from glare related problems. An example of a transmissive lens is shown in Fig. 13. As may be seen from Fig. 19a, a major part of the rays emitted by the lighting system is confined within a cone with 45° half angle. More particularly, nearly all rays are confined within a cone with 65° half angle.

The second simulation, the result of which is shown in Fig. 19b, is based on reflective lenses with a spherical shape (also non-optimal). An example of a reflective lens is shown in Fig. 17 and Fig. 18a -18c. As may be seen from Fig. 19b, nearly all of the rays emitted by the lighting system are confined within a cone with 10° half angle.

Furthermore, in Fig. 20, there is shown an exemplifying lighting system according to the present invention. The lighting system comprises the light guide 5, scattering dots (or out-coupling dots) 20 and transmissive Fresnel-type lenses 32. Further, there are disposed mirrors 35 at the top (as shown in Fig. 20) surface of light guide. The top surface of the light guide is further equipped with a diffuser 34. A diameter d_m of the mirror is selected such that an angle θ is less than the angle of TIR. In this manner, some light will escape out of the light guide at the top surface of the light guide. Such a lighting system combines functional (direct) light emitted downwards with indirect light (illumination of the ceiling) emitted upwards. By tuning the diameter of the mirror, which may be circular, it is possible to adjust the ratio of direct light to indirect light.

With reference to Fig. 21 , there is shown a portion of an exemplifying embodiment of the present lighting system. The lighting system comprises a light guide 5, scattering dots 20, a diffuser 34 and mirrors 35 with a diameter d_t. The scatting dots 20 are disposed at the bottom (as seen in the Figure) surface of the light guide 5 and the mirrors 35 are disposed at the top (as seen in the Figure) surface of the light guide 5. Preferably, the mirrors 35 are not in optical contact with the light guide 5. The function of the top mirrors is to reflect the light that is scattered upwards by the dots. Suppose for the sake of the argument that the size of the dots is small compared to the thickness t of the light guide 5. Now consider a ray leaving a dot at an angle θ. The size of the top mirror (d_t) is chosen such that all rays with θ not exceeding a certain value will leave the light guide through the bottom surface within a cone with cut-off angle θ_cut__Off. In this case, it can be derived that d_t should fulfill the relation: d_t = 2t tan[asin((l/n) sin(θ_cut__Off))].

In this equation, n is the index of refraction of the light guide 5. If choosing θcut off = 60° in air, the light source will fulfill the glare norm. Together with n=1.49 (PMMA), dt=1.43t. Rays at larger values of θ will leave the light guide at the upper side. They will leave the light guide at grazing angles. The direction of these rays may be changed to more upright by means of a redirection layer or a diffuser 34. Rays with even larger values of θ (i.e. rays exceeding the critical angle for TIR; θ > θ_c = asin(l/n) will be guided inside the light guide by total internal reflection. These rays will travel along the light guide until they encounter a scattering dot 20 again.

A further exemplifying embodiment of the lighting system is shown in Figure 22. This example is similar to the example in Fig. 21. However, the top mirror is chosen somewhat larger than the mirror in Fig. 21. Further, there is disposed a bottom mirror at the bottom surface of the light guide. The mirror is in the form of a mask with holes or openings. The mirror is used to redirect the rays that are to be coupled out at the top side. The radius of the holes in the mirrors at the bottom side determines the cut-off angle Θ_cut-_Off.

In further examples of the lighting system, the appearance of the system may be changed. The appearance of the lighting system is to a large extent determined by the bottom side of the mask (or the shaping means). The mask holes may be given a certain shape for functional reasons as has been explained above, but the shape of the holes or openings may also be determined by design considerations alone or in combination with functional reasons.

The previous examples are based on square, rectangular or hexagonal arrays of dots (means for providing light) and holes (shaping means) with a constant pitch.

Nevertheless, the array may be of any shape (triangular, irregular, etc.). As for the hole shape, this may be for functional reasons (e.g. vary the pitch with distance to the source in order to achieve a more homogeneous distribution, or use clusters of holes at a small pitch to concentrate light at certain locations). These parameters may also be changed as a result of design considerations (e.g. arrange the holes in a star shape or along a pattern of lines). The non-transmissive part of the shaping means (e.g. the mask) may be completely determined by design considerations. For example, it may feature a print that matches the interior design. In this manner, the lighting system blends well with its surroundings and will be very unobtrusive in the off-state. The mask may also be slightly translucent, but sufficiently blocking to keep the cutoff below glare regulations, to give the lighting system an appearance of glowing. This will be particularly visible at large angles (long distance) to the lighting system, because at long distances (and large angles) the direct light contribution is cut off. By using a (reflective) color filter in the (slightly) translucent mask, the lighting system is given a color that will be complementary to the color effect given to the indirect light. For example, if the mask allows some blue light to pass, the lighting system will look bluish, whereas the indirect (reflected) light will look yellowish.

The lighting system may also be given a colored glowing appearance by applying a thin light source (at low light levels) at the bottom side of the mask, such as an OLED or a thin light guide fed by inorganic colored LEDs.

In further examples of the lighting system, the scattering dots are arranged to have a constant size and spacing, but with varying scattering strength. There are several ways to achieve this including for example, or a combination of, dots having a variable dithering, dots of paint having a variable thickness, and/or sandblasted surface dots having a variable roughness. The reason for this implementation is due to the use of a side-lit light guide where the intensity generally decreases with increasing distance from the sides where light is coupled in from for example an LED. In conventional backlighting systems, this effect is countered by varying the scattering (i.e. out-coupling) dots in size and/or in spacing. However, in the present invention, the dot size and spacing is strongly coupled to the beam profile via the size and spacing of the reflective mask. Hence a uniform appearance in the lit state (with varying dot size or spacing) would result in a non-uniform appearance of the mask in the unlit state. For example, turning back to figure 4, it is clear that the scattering elements cannot be varied in size or pitch without changing the beam profile and/or the mask pattern. This is less preferred since this may cause glare (or possibly an inhomogeneous appearance of the luminaire in the off-state since the mask hole size and pitch must vary along with the dot pattern).

Accordingly, it may be possible to improve the luminance uniformity along the light guide by varying the out-coupling efficiency of the scattering elements without varying the element size or pitch. Four examples of scattering dots are illustrated in Fig 23a- 23 d.

In Fig 23a, the distances Di - D₃ between the light sources (e.g. LEDs 50) and the scattering dots 20 will have an impact on the amount of out-coupled light, which will decreases with increasing distance from the sides where light is coupled in from for example an LED.

However, in Fig. 23b, the distances Di - D₃ between the light sources and the scattering dots 20, 20', 20", respectively, controls the selected out-coupling efficiency provided by the dots, wherein the outcoupling efficiency is tuned by varying the size of the blank circle inside the dot, in this embodiment by adjusting the amount of white paint such that the dots only are partially filled with white paint.

Similarly, in Fig. 23 c, the distances Di - D3 between the light sources and the scattering dots 20, 20', 20", respectively, controls the selected out-coupling efficiency provided by the dots, wherein a partial filling of dots by dithering has been implemented. In this case, the scattering dots 20' and 20" consist of small patches of paint and/or surface roughness, and thus, the out-coupling efficiency depends on the density of patches in the dot area. The essence is that the total dot area is only partly covered by scattering surface, at least in relation to the dots 20' and 20". This partial covering may have a high spatial frequency (dithering) or a low spatial frequency (e.g. rings of variable thickness).

Additionally, it is also possible to vary the thickness of white paint dots. That is, thick paint dots are fully reflective, and by reducing the thickness, the scattering elements may also become partly transmissive, such that the amount of light that is outcoupled via the mask holes can be tuned. Also, it is possible to provide a variable roughness of the surface scattering elements (e.g. sandblasted dots). In such an implementation, the out-coupling efficiency can be tuned by varying the ratio between the specular and the diffuse component of the scattering dots. It should also be noted that it may be possible to combine any of the above techniques.

Turning finally to Fig 23d, where a cross-sectional view of a typical light guide with out-coupling dots of variable transmission is illustrated. On the left, closest to the side emitting LED 50 emitting light into the light guide 5, the dot 20" having thin white paint scatters less light downwards than the right thick dot 20' further away from the LEDs 50, thereby achieving a more uniform appearance.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. The described embodiments are therefore not intended to limit the scope of the invention, as defined by the appended claims.

Claims

CLAIMS:

1. A lighting system (1), comprising: a light guide (5), having a first and a second surface facing each other, at least one of said surfaces being capable of providing light in a first direction (100, 200), means capable of providing light (20), said means capable of providing light being disposed at at least one of said surfaces, and means for shaping light (30, 31, 32, 35, 36) from said means capable of providing light, said shaping means being arranged to shape light in said first direction.

2. The lighting system (1) according to claim 1, wherein said light guide (5) guides light from said means capable of providing light to said shaping means (30, 31, 32, 35, 36).

3. The lighting system (1) according to any one of the preceding claims, wherein said lighting system comprises an array of means capable of providing light and an array of shaping means.

4. The lighting system (1) according to any one of the preceding claims, wherein each means capable of providing light is associated with a respective shaping means.

5. The lighting system (1) according to any one of the preceding claims, wherein said shaping means (30, 31, 32, 35, 36) further is arranged at at least one of said surfaces.

6. The lighting system (1) according to any one of the preceding claims, wherein said shaping means (30, 31, 32, 35, 36) comprises a mask with at least one opening for shaping of light emitted in said first direction, said mask being disposed at said first surface.

7. The lighting system (1) according to claim 6, wherein said mask comprises a retro-reflecting material at a side of the mask facing said second surface, whereby increased light flux in the first direction is achieved.

8. The lighting system (1) according to claim 6, wherein said mask comprises a mirror, wherein a reflective surface of said mirror is arranged to face said second surface.

9. The lighting system (1) according to any one of claims 1-8, wherein said shaping means comprises a lens for shaping light emitted in said first direction.

10. The lighting system (1) according to claim 9, wherein said lens has a first refraction ability within a radius of the lens and a second refraction ability outside said radius of the lens.

11. The lighting system (1) according to claim 9 or 10, wherein said lens comprises a transmissive lens, preferably a Fresnel-type lens, said lens being disposed at said first surface.

12. The lighting system (1) according to claim 9 or 10, wherein said lens comprises a reflective lens, said lens being disposed at said second surface.

13. The lighting system (1) according to any one of claims 1-11, wherein said shaping means (30, 31 , 32, 35, 36) comprises a mirror, preferably a circular mirror, for directing light in said first direction, wherein said mirror is disposed said second surface and a reflective surface of said mirror is arranged to face said first surface.

14. The lighting system (1) according to any one of claims 1-10, 12-13, wherein said means capable of providing light is arranged at said first surface.

15. The lighting system (1) according to any one of claims 1-11, wherein said means capable of providing light is arranged at said second surface.

16. The lighting system (1) according to any one of the preceding claims, wherein said first surface is capable of providing light in said first direction.

17. The lighting system (1) according to any one of the preceding claims, wherein said second surface is capable of providing light in a second direction.

18. The lighting system (1) according to any one of the preceding claims, wherein shaping of light in said first direction is dynamically controllable.

19. The lighting system (1) according to any one of the preceding claims, wherein shaping of light in said second direction is dynamically controllable.

20. The lighting system (1) according to claim 18 or 19, wherein said dynamic control is provided by any one of mechanical or electrical means or a combination thereof.

21. The lighting system (1) according to claim 20, wherein said mechanical means is arranged to change the physical relation between said shaping means and said means capable of providing light.

22. The lighting system (1) according to claim 20 or 21, wherein said electrical means is provided by means of any one of a switchable reflector, a switchable electro -chromic layers or a switchable diffusers, such as liquid crystal gel and/or polymer dispersed liquid crystals, or a combination thereof.

23. The lighting system (1) according to any one of the preceding claims, wherein said means capable of providing light (20) comprises any one of dots comprising a phosphor-based material, dots of paint, holographic diffusers, optical structures for refracting and/or reflecting light, LEDs or organic LEDs or a combination thereof.

24. The lighting system (1) according to claim 23, further comprising a primary light source, and wherein said dots have a scattering strength depending on the relative distance to the primary light source.

25. The lighting system (1) according to claim 24, wherein the dots are at least one of dots having a variable dithering, dots of paint having a variable thickness and dots having a variable roughness, and the variation depends on the relative distance to the primary light source.

26. The lighting system (1) according to any one of claims 1-22, further comprising a primary light source, and wherein said means (20) capable of providing light comprises a secondary light source.

27. The lighting system (1) according to claim 26, wherein said means capable of providing light comprises microstructures comprising facets at about 45° to a normal of any one of said surfaces and said primary light source provides collimated light incident on said light guide in a direction substantially perpendicular to said first and second direction.

28. The lighting system (1) according to claim 26 or 27, wherein said primary light source is arranged to emit light incident on said means capable of providing light.

29. The lighting system (1) according to any one of claims 26-28, wherein said primary light source comprises an LED, an organic LED, a fluorescent lamp or alike or a combination thereof.