WO2005031411A1

WO2005031411A1 - Lighting system, light chamber and display device

Info

Publication number: WO2005031411A1
Application number: PCT/EP2004/052276
Authority: WO
Inventors: Jacobus Johannes Fiers
Original assignee: Fivado Beheer B.V.
Priority date: 2003-09-29
Filing date: 2004-09-23
Publication date: 2005-04-07
Also published as: NL1024395C2

Abstract

A lighting system for lighting an image (13) comprises a light-emitting panel (1) comprising a light output window (2) and a rear wall (3) disposed opposite thereto. At least one light ingress surface (4) is located between the light output window (2) and the rear wall (3) for coupling light from a light source (6) into the light-emitting panel (1), wherein, in use, the light propagates through the light-emitting panel (1). According to the invention, the light output window (2) is provided with a pattern of light-diffusing element (8, 8', …). Preferably, the pattern of light-diffusing elements (8, 8', ...) comprises a multitude of discrete markings on the surface of the light output window (2). Preferably, the markings are at least substantially homogeneously distributed over at least substantially the entire surface of the light output window (2). The uniformity of the light distribution of the lighting system, and thus the evenness with which the image is lighted, has been improved.

Description

Lighting system, light chamber and display device

The invention relates to a lighting system for lighting an image, comprising a light-emitting panel comprising a light output window, a rear wall disposed opposite thereto, and furthermore at least one light ingress surface located between the light output window and the rear wall for coupling light from a light source into the light-emitting panel, wherein, in use, the light propagates through the light-emitting panel. The invention furthermore relates to a light chamber for use in said lighting system and to a display device provided with said lighting system. Such lighting systems, which are known per se, are also referred to as edge lighting systems. They are used inter alia for back-lighting translucent images, e.g. a sheet of paper, a film, a foil or a (colour) photograph, e.g. for advertising purposes in shops, offices, bus shelters and at exhibitions, for example. Furthermore, the lighting systems are used for signposting purposes (both indoors and outdoors), e.g. at airports and in public buildings. Such lighting systems are furthermore used for decorative purposes. In the lighting systems as referred to in the introduction, the light source is usually a tubular low-pressure mercury discharge lamp, e.g. one or more compact fluorescent lamps, wherein the light that is emitted by the light source in use is coupled into the light-emitting panel, which functions as a light guide. Said light guide generally forms a relatively thin and flat panel, e.g. made of a plastic or glass, with light being transmitted through the light guide inter alia under the influence of (total) internal reflection. Such a lighting system may also be provided with a multitude of optoelectronic elements, e.g. light-emitting diodes (LED's), as an alternative light source. Another alternative light source is a laser diode. These light sources are generally disposed near or abut against a light ingress surface of the light-emitting panel, wherein, in use, light from the light source is incident on the light-transmitting edge surface and propagates through the panel. From WO-A 02/50473 there is known a lighting system which comprises a light-emitting panel and one or more light sources, which couple light into the light-emitting panel via a light ingress surface, which light subsequently propagates through the light- emitting panel. The light ingress surface is located between a light output window and the rear wall of the light-emitting panel. In the known lighting system, the distribution of the light being emitted by the light-emitting panel is effected by providing a suitable pattern of light-diffusing elements on the rear wall of the light-emitting panel. A drawback of the lighting system of the above type is that the light distribution in the light-emitting panel is not uniform enough. As a result, the lighting of the image does not take place sufficiently evenly.

The object of the invention is to obviate the above drawback in whole or in part. More in particular it is an object of the invention to provide a lighting system of the type referred to in the introduction wherein the distribution of light takes place more uniformly, resulting in a more even lighting of the image. According to the invention, this objective is accomplished in that the light output window is provided with a pattern of light-diffusing elements. Light-diffusing elements typically scatter light. Preferably, the light-diffusing elements scatter the light in every direction, e.g. according to a so-called Lambert distribution. Part of the light can egress the light-emitting panel via the light output window in this way and can be used for lighting the image. By varying the size, the shape and the position of the light-diffusing elements, the aperture of the light output window is influenced. By varying the aperture, the internal reflection in the light-emitting panel is influenced, and thus the light distribution in the light-emitting panel. As the number of internal reflections increases, the light distribution in the light-emitting panel becomes more homogeneous, and the light output of the light-emitting panel decreases as a result of the increasing attenuation. As the number of internal reflections decreases, the light distribution in the light-emitting panel becomes less homogeneous, and the light output increases as a result of the decreased attenuation. A suitable selection of the size, the shape and the position of the light-diffusing elements leads to a homogeneous light distribution in combination with a relatively high light output. In the known lighting system, a pattern of light-diffusing elements is provided on the rear wall of the light-emitting panel. In the lighting system according to the invention, a pattern of light-diffusing elements is provided on the light output window of the light- emitting panel. As a result, the light distribution in the light-emitting panel is controlled in combination with the amount of light being emitted by the light output window. This aspect according to the invention leads to an improved uniformity of the distribution of the light being emitted by the lighting system. As a result, a more even lighting of the image to be displayed is realised. Another advantage of providing a lighting system according to the invention is the fact that simpler and/or cheaper images can be used, which images will nevertheless have an attractive appearance. The appearance of the image obtained by using the lighting system according to the invention has thus been improved. As a result of the improved uniformity of the light distribution, the designer of the image to be displayed has a wider technical scope in designing the image. Thus it is possible to use an even background colour. If an even background colour would be used in the known lighting system, small variations in the light distribution would be readily perceptible to the viewer. Preferably, the pattern of light-diffusing elements comprises a multitude of discrete markings on the surface of the light output window. Such markings, also called spots, are relatively easy to provide on the surface of the light output window. Special effects can be realised by varying the dimension of the markings and the distribution of the markings over the surface of the light output window. In this way the attractiveness of the image being displayed can be enhanced. Preferably, the markings are at least substantially homogeneously distributed over at least substantially the entire surface of the light output window. In this way the image to be displayed by the lighting system is lighted as evenly as possible. An advantageous embodiment of the lighting system is characterized in that the number of markings per unit area varies between 10 and 50 markings per cm², preferably between 16 and 25 markings per cm². Given the dimensions of and the spacing between the markings, the aperture of the light output window is adjustable from about 20% to about 80%. Preferably, the markings form small protrusions on the surface of the light output window. Preferably, the shape of said markings has been selected from the group consisting of spheres, cones, pyramids, and parallelepipeds and parts of spheres, cones, pyramids, and parallelepipeds. Such shapes are relatively easy to provide on the surface of the light output window. A preferred embodiment of the lighting system is characterized in that the rear wall is provided with a reflective layer on a side remote from the light-emitting panel. Such a reflective layer increases the light output of the lighting system. Preferably, said reflective layer is diffusely reflective. Such a diffusely reflective layer increases the homogeneity of the light distribution in the light-emitting panel. The diffusely reflective layer enlarges the viewing angle of the lighting system. The reflective layer is preferably spaced from the rear wall. Such a reflective layer can simply be provided as a loose layer in the lighting system, e.g. in the form of a reflective foil. An alternative, preferred embodiment of the lighting system is characterized in that the reflective layer is provided with a pattern of light-diffusing elements on a side facing towards the light-emitting panel. Preferably, the pattern of light-diffusing elements comprises a multitude of discrete markings on the surface of the reflective layer. The provision of a second scattering layer causes the number of internal reflections in the light- emitting panel to increase. An advantageous embodiment of the lighting system is characterized in that the light output window is provided with a light-diffusing layer on a side remote from the light-emitting panel. Such a light-diffusing layer enlarges the viewing angle of the lighting system. The light-diffusing layer is preferably spaced from the light output window. This simplifies the assembly of the lighting system. An alternative, preferred embodiment of the lighting system is characterized in that a light chamber for accommodating a light source is associated with the light ingress surface, and in that the light chamber is provided with a reflective foil or layer for directing, in use, the light from the light source to the light ingress surface. The light chamber according to the invention is of simple construction and can be manufactured at low cost. The reflective foil or layer causes the light from the light source to be directed to the light ingress surface of the light-emitting panel. The reflective foil or layer preferably extends over part of the light output window and or the rear wall of the light-emitting panel. Such construction contributes towards the coupling of light from the light chamber into the light- emitting panel.

The invention will now be described in more detail on the basis of a number of embodiments and a drawing. In the drawing: Fig. 1 shows an embodiment of the lighting system according to the invention in cross-sectional view; Fig. 2 shows an alternative embodiment of the lighting system according to the invention in cross-sectional view; Fig. 3 shows a further alternative embodiment of the lighting system according to the invention in cross-sectional view; and Fig. 4 shows the luminance of the light measured at the light output window of the lighting system as shown in Figs. 1 and 3. The figures are purely schematic illustrations, which are not drawn to scale.

More in particular, some dimensions are strongly exaggerated for the sake of clarity. Like parts are indicated by the same numerals as much as possible in the figures.

Fig. 1 schematically shows an embodiment of the lighting system according to the invention in cross-sectional view. The lighting system comprises a light-emitting panel 1 of a light-transmitting material. The panel 1 is e.g. made of a plastic, acryl, polycarbonate, PMMA, e.g. perspex, or glass. A very suitable material having a high optical brightness is methyl methacrylate (MMA). The light-emitting panel may have a variety of dimensions. This aspect of the invention makes it possible to use relatively large light-emitting panels, too. Lighting systems having panel dimensions LxWxT = 2000x3000x10 mm in which the uniformity of the light distribution is retained have been realised. L represents the length of the panel, W represents the width of the panel and T represents the thickness of the panel. An especially suitable lighting system has a light-emitting panel of e.g. Al-size, wherein LxWxT = 935x630x10 mm. In use, light is transmitted through the panel 1 under the influence of total internal reflection. The light-emitting panel 1 has a light output window 2 and a rear wall 3 disposed opposite thereto. Furthermore a light ingress surface 4 is disposed between the light output window 2 and the rear wall 3 for coupling light from a light source 6 into the light- emitting panel 1. The lighting system further comprises a light chamber 5 (very schematically indicated in Fig. 1) provided with a light source 6. The light chamber in Fig. 1 is provided with a hinge 5' for providing easy access to the lighting system. Usually a tubular low-pressure mercury discharge lamp, e.g. one or more (compact) fluorescent lamps, is used as the light source 6. Alternatively, a multitude of optical-electronic elements, e.g. light- emitting diodes (LED's), are used as the light source. One light chamber suffices for lighting systems of relatively small dimensions. For lighting systems of relatively large dimensions, two light chambers are usually used on opposed sides of the light-emitting panel. The light chamber(s) preferably extend(s) parallel to the long side(s) of the light-emitting panel. The light chamber 5 is associated with the light ingress surface 4, which means that the light chamber 5 is coupled to the light ingress surface 4 in such a manner that the light that is generated in the light chamber 5 is optimally coupled into the light-emitting panel 1 via the light ingress surface 4. In use, light from the light source 6 is incident on the light-transmitting edge surface 4 and propagates through the light-emitting panel 1. The light from the light source 6 can reach the light ingress surface both directly and via (multiple) reflections on the walls of the light chamber 5. In Fig. 1 the light chamber 5 is furthermore provided with a reflective foil 7 or layer for directing light from the light source 6 to the light ingress surface 4 in use. In the example of Fig. 1, the reflective foil 7 extends over part of the light output window 2 and of the rear wall 3 of the light-emitting panel 1. This contributes towards the coupling of light from the light chamber 5 into the light-emitting panel 1. A diffuser (not shown) may be present between the light chamber 5 and the light ingress surface 4 for the purpose of contributing towards the mixing of the light from the light chamber 5. Preferably, such a diffuser does not form an additional interface between the light chamber 5 and the light-emitting panel 1. The light chamber 5 can be made in a simple manner, it will e.g. comprise a housing of suitably folded sheet metal. A sensor (not shown in Fig. 1) may be provided in the light chamber 5 for measuring the optical properties of the light that is being emitted by the light source 6 in use. Said sensor is connected to control electronics (not shown in Fig. 1) for suitably adapting the flow of light from the light source 6 to the desired brightness and/or colour point of the light to be output by the light-emitting panel. A feedback mechanism can be realised by means of the sensor and the control electronics for influencing the quality and the quantity of the light to be output from the light-emitting panel 1. In Fig. 1, numeral 13 indicates a (translucent) image to be displayed by the lighting system. Suitable translucent images are e.g. a sheet of paper or a foil provided with an illustration, a film image or a (colour) photograph. Also combinations of images are possible. The assembly of the light-emitting panel 1, the light source 6 and the image 13 forms a display device, e.g. for displaying (video) images. In the example of Fig. 1 a protective layer 15 is provided for protecting the image 13, e.g. against scratches or stains. The light being emitted by the light-emitting panel lights the translucent image 13 and egresses the lighting system in the manner indicated by the arrows in Fig. 1. In order to increase the light output of the lighting system, the rear wall 3 of the light-emitting panel 1 is provided with a reflective layer 9 on a side remote from the light-emitting panel 1. In the example of Fig. 1, the reflective layer 9 is spaced from the rear wall 3. In an advantageous embodiment, the reflective layer 9 is diffusely reflective. To enlarge the viewing angle of the lighting system, the light output window 2 is provided with a light-diffusing layer 11 on a side remote from the light-emitting panel 1. In the example of Fig. 1, the light-diffusing layer 11 is spaced from the light output window 2. According to the invention, the light output window 2 of the light-emitting panel 1 is provided with a pattern of light-diffusing elements 8, 8', ... . The pattern of the light-diffusing elements 8, 8', ... preferably comprises a multitude of discrete markings on the surface of the light output window 2. The markings are preferably homogeneously distributed over the surface of the light output window 2. In this way the image to be displayed by the lighting system is lighted as evenly as possible. Special effects can be realised by varying the dimension of the markings and the distribution of the markings over the surface of the light output window 2. By way of example, certain parts of the surface of the light output window 2 may thus emit more light than other parts; in this way the corresponding parts of the image can be made to stand out relative to the surrounding parts (e.g. the product itself or a halo around the product), which enhances the attraction of the product being displayed. The number of markings per unit area preferably varies between 10 and 50 markings per cm². An especially suitable number of markings per unit area is 16-25 markings per cm². Preferably, the dimension of the markings varies between 1 and 2.5 mm and the spacing between the markings varies between 0.5 and 2.5 mm. Given the dimension of the markings and the spacing therebetween, the aperture of the light output window can be adjusted between about 20% and about 80%. The height of the markings varies from 0.002 to 0.25 mm, with a height of 0.10 to 0.15 mm being especially suitable. The markings preferably form small protrusions on the surface of the light output window. Said markings comprise (patterns of) deformations, e.g. comprising screen- printed dots, wedges and/or corrugations. The markings have been formed in the light output window 2 of the panel 1 by etching, scratching or sandblasting, for example. Alternative ways of forming the markets are grinding, laser treatment or cutting. The markings may be flat, convex and/or polygonal. Very suitable markings are spheres, cones, pyramids, and parallelepipeds and parts of spheres, cones, pyramids, and parallelepipeds. Such shapes are relatively easy to form on the surface of the light output window, e.g. by means of roller printing or screen-printing techniques. The markings function as a secondary light source and output light from the light-emitting panel 1 by reflection, diffusion and/or refraction. The markings, which are irradiated from the light-emitting panel 1, typically scatter the light in all directions. As a result, part of the light egresses from the light-emitting panel 1 and part of the light is reflected and remains within the light-emitting panel 1. The aperture of the light-emitting panel can be regulated between 23% and 77% by a suitable selection of the dimension, the shape and the position of the light-diffusing elements. By varying the aperture, the internal reflection of the light-emitting panel is influenced and the light distribution is adapted to the dimension of the light-emitting panel 1. In this way a lighting system exhibiting a homogeneous light distribution in combination with a relatively high light output is effected. Fig. 2 schematically shows an alternative embodiment of the lighting system according to the invention in cross-sectional view. Like parts are indicated by the same numerals in Figs. 1 and 2. In Fig. 2, the light-emitting panel 1 is provided with a pattern of light-diffusing elements 18, 18', ... . Preferably, the pattern of light-diffusing elements 18, 18', ... comprises a multitude of discrete markings on the surface of the reflective layer 9. The provision of a second scattering layer causes the number of internal reflections in the light-emitting panel 1 to increase. In an alternative embodiment of the lighting system (not shown in Fig. 1) the rear wall 3 is provided with a pattern of light-diffusing elements, which pattern preferably comprises a number of discrete markings on the surface of the rear wall 3. In the example of Fig. 2, the reflective foil 7 comprises a trapezoidal mirror built up of one or more mirror parts. The location of the mirror parts is preferably selected so that the reflected light is not directed back towards the light source 6. Preferably, the trapezoidal mirror that is used is designed so that the light source 6 becomes readily accessible when the light chamber 5 is opened via the hinge 5'. Fig. 3 schematically shows another alternative embodiment of the lighting system according to the invention in cross-sectional view. Like parts are indicated by the same numerals in Figs. 1 and 3. In the lighting system as shown in Fig. 3, the rear wall 3 also functions as a light output window and is provided with a pattern of light-diffusing elements 28, 28', ... . In Fig. 3, a light-diffusing layer 11, 11', an image 13, 13' and a protective layer 15, 15' are present on either side of the light-emitting panel. The light that is emitted by the light-emitting panel in Fig. 3 illuminates the translucent images 13, 13' and egresses the lighting system on opposite sides as indicated by the arrows in Fig. 3. Fig. 4 shows the luminance L_u of the light measured at the light output window as shown in Figs. 1 and 3. In both cases a lighting system having a length of about 0.94 metres is concerned, in which a light chamber provided with a light source is present on both sides. The luminance measurements have been carried out without an image being present in the lighting system. Curve (1) shows the luminance as a function of the distance from the lighting system that emits unilateral light (Fig. 1). Curve (2) shows the luminance as a function of the distance from the lighting system that the units bilateral light (Fig. 2). Near the edges of the light output window a minor effect of the coupling of the light from the light chamber can be detected. The measurements show that the light distribution is sufficiently uniform all over the light output window of the light-emitting panel, also near the light source. A sufficiently even lighting of the image is realised with the lighting system according to the invention. It will be apparent that many variations are open to those skilled in the art within the framework of the invention. The scope of the invention is not limited to the embodiments as shown herein. The scope of the invention extends to each and every new aspect and each and every combination of aspects. The use of the word "comprising" does not exclude the presence of elements other than those mentioned in the claims. The use of the word "a" or "an" preceding an element does not exclude the presence of a multitude of such elements.

Claims

CLAIMS:

1. A lighting system for lighting an image (13), comprising a light-emitting panel (1) comprising a light output window (2), a rear wall (3) disposed opposite thereto, and furthermore at least one light ingress surface (4) located between the light output window (2) and the rear wall (3) for coupling light from a light source (6) into the light-emitting panel (1), wherein, in use, the light propagates through the light-emitting panel

(1), characterized in that the light output window (2) is provided with a pattern of light-diffusing elements (8, 8', ...).

2. A lighting system as claimed in claim 1 , wherein said pattern of light- diffusing elements (8, 8', ...) comprises a multitude of discrete markings on the surface of the light output window (2).

3. A lighting system as claimed in claim 2, wherein said markings are at least substantially homogeneously distributed over at least substantially the entire surface of the light output window (2).

4. A lighting system as claimed in claim 2 of 3, wherein the number of markings per unit area varies between 10 and 50 markings per cm², preferably between 16 and 25 markings per cm².

5. A lighting system as claimed in claim 2, 3 of 4, wherein the shape of said markings has been selected from the group consisting of spheres, cones, pyramids, and parallelepipeds and parts of spheres, cones, pyramids, and parallelepipeds.

6. A lighting system according to any one of the preceding claims, wherein the rear wall (3) is provided with a reflective layer (9) on a side remote from the light-emitting panel (1).

7. A lighting system as claimed in claim 6, wherein said reflective layer (9) is diffusely reflective.

8. A lighting system as claimed in claim 6 of 7, wherein said reflective layer (9) is spaced from the rear wall (3).

9. A lighting system as claimed in claim 6, 7 of 8, wherein said reflective layer (9) is provided with a pattern of light-diffusing elements (8, 8', ...) on a side facing towards the light-emitting panel (1).

10. A lighting system as claimed in claim 9, wherein the pattern of light-diffusing elements (18, 18', ...) comprises a multitude of discrete markings on the surface of the reflective layer (9).

11. A lighting system according to any one of the preceding claims, wherein the light output window (2) is provided with a light-diffusing layer (11) on a side remote from the light-emitting panel (1).

12. A lighting system as claimed in claim 11, wherein the light-diffusing layer (11) is spaced from the light output window (2).

13. A lighting system according to any one of the preceding claims, wherein a light chamber (5) for accommodating a light source (6) is associated with the light ingress surface (4), and in that the light chamber (5) is provided with a reflective foil (7) or layer for directing, in use , the light from the light source (5) to the light ingress surface (4).

14. A lighting system as claimed in claim 13, wherein the reflective foil (7) or layer extends over part of the light output window (2) and/or the rear wall (3) of the light- emitting panel (1).

15. A lighting system according to any one of the preceding claims, wherein said rear wall (3) also functions as a light output window and is provided with a pattern of light- diffusing elements (28, 28', ...).

16. A light chamber (5) for use in a lighting system as claimed in claim 13 or 14.

17. A display device provided with a lighting system according to any one of the preceding claims.

18. A display device as claimed in claim 17, wherein the display device is provided with a image (13), for example a photo.