WO2004104476A1

WO2004104476A1 - Thin flat lamp module for shelf illumination

Info

Publication number: WO2004104476A1
Application number: PCT/DK2004/000352
Authority: WO
Inventors: Karl Lausten
Original assignee: Bright Ideas V/Karl Lausten
Priority date: 2003-05-20
Filing date: 2004-05-18
Publication date: 2004-12-02
Also published as: EP1625326A1; DK200300756A; DK176001B1

Abstract

A thin flat lamp module using Light Emitting Diodes (LED) or other miniature light sources with low heat dissipation in combination with a light guide including an optical lens and a curved mirror to emit light perpendicular to the module or in any angle or range of angles between approx. 40 and 140 degrees. Useful application is for illumination of shelves and other confined spaces. The module may be mounted underneath a shelf near the front of that shelf thus illuminating the shelf below and any objects on it. Modules may be interconnected to build a uniform lamp of some length with one common power supply.

Description

Thin flat lamp module for shelf illumination

Technical field

The invention concerns a lamp module having a light source optically coupled to the rear of a light guide for propagation of light to the front end of the light guide, where the front end of the light guide is provided with a reflective surface for reflecting light out of the light guide. The invention further concerns a shelf system with such a lamp module and use of such a lamp module.

Background of the invention

Shelf illumination has had a number of drawbacks including undesired heat dissipation, space consumption, poor angle of illumination, and necessity to encroach on the construction to make way for the light and/or for ventilation or at least to mount the lamp. Shelf illumination has utilised incandescent or fluorescent light sources both of which produce heat to an extent that demands ventilation and a certain minimum space around the light source to avoid fire hazards. The light sources themselves are rather spacious and in many cases demand high voltage power supply and correspond- ingly safe electrical insulation.

In shelf systems, the light source often has been placed behind one shelf and shielded in such a way that light would not shine directly towards the front but instead be reflected from the back wall or from the shelf above or below. Or the light source has been placed centred over the top shelf emitting a conical light beam passing through several shelves made of glass or other transparent material - the lower shelves being partly shaded by objects placed on upper shelves. Neither solution produces satisfying illumination, and both are spacious and encroach on the construction.

Lately, solid state lighting has become available, practically eliminating heat dissipation and to some extent decreasing demand for space. However, a lamp has not yet been constructed in a way that gives an optimal angle of illumination and at the same time requires very little space and does not encroach on the bookcase or cupboard. Cold Cathode Fluorescent Lighting is an alternative for diminutive light sources without excessive heat dissipation that has not been utilised for this purpose.

In Japanese patent application JP 2002 042 408 by Atsumi Kensaku assigned to Mat- sushita Electric Works Ltd, a shelf illumination is disclosed with a light guide having a skew plane at the end for refraction of light out of the light guide. The skew plane results in an illumination of the surroundings at the end of the light guide as well as in an opposite direction. However, due to the angular spread of the light in the light guide, this system is not suited for a controlled illumination in certain possibly naroow directions.

In british patent GB 952,388 by Ernest Raymond Constance, an illuminated transparent display shelf is disclosed, where light from a light guide has a saw-tooth configuration on its lower side for reflecting light out of the upper part of the light guide in order to illuminate objects standing on the transparent shelf.

A light guide with a saw-tooth reflector for a fax machine is also disclosed in Japanese patent application JP 2003 097 910 by Kawana Takashi assigned to Canon KK. This system is provided for an even illumination in near vicinity of the light guide.

The aforementioned systems are not construed for a controlled spread of light into certain directions with possible rather narrow angular spreads, for example in connection with book shelves or pictures.

It is therefore the purpose of the invention to provide a light source in a low profile environment, preferably for book and display shelves, which only has a very low heat dissipation, which is small and which delivers light at a predetermined direction, preferably suited for downwards or sideways directed shelf illumination.

Summary of this invention

This purpose is achieved by a lamp module having a light guide with a rear end and a front end and a side surface between the rear end and the front end, the module further comprising at least one light source optically coupled to the rear end of the light guide, the front end of the light guide being provided with a reflective surface for reflecting light from the light source after propagation through the light guide, wherein the reflective surface is a curved mirror configured to reflect light from the light source through an exit region at the side surface.

By using a mirror, the light may be reflected in a desired direction, also into rather narrow angles dependent on the form of the mirror. Furthermore, the mirror may be provided for an even illumination in such directions.

The side surface, preferably, comprises two parallel distant planes, and the invention will be explained in this respect in the following. However, many other shapes are possible, for example a cylindrical or wedge-shaped light guide, or a bent light guide using a mirror or internal reflection at the bend.

As a light source, a light emitting diode (LED) may be used. The optical coupling be- tween the light source and the light guide may comprise a curved rear end of the light guide constituting a cylindrical lens for transforming divergent light rays from the light source into parallel fans of rays inside the light guide.

Alternatively, the optical coupling between the light source and the light guide com- prises a double-curved rear surface, the curvature of which is convex in a first direction for transforming divergent light rays from the light source into parallel fans of rays inside the light guide, and concave in a perpendicular direction in order to increase the spread of the fans of rays inside the light guide.

Instead of using LEDs, it is possible to use Cold Cathode Fluorescent Lighting (CCFL), wherein the optical coupling between the light source and the light guide comprises a reflector surrounding those parts of the light source not facing the light guide and arranged to reflect the light from the light source towards the rear end of the light guide. The optical lens in the form of a cylindrical curved rear surface may in this case be replaced by a straight edge as the light source is supplied with a reflector.

The curved mirror at the front end may be convex or concave with a reflecting surface having a shape adapted to the intensity profile desired at the exit region. For example, the mirror may be configured to reflect the light from the light source into angles be- tween approximately 40 and 140 degrees outside the exit surface of the light guide. Preferably, the mirror has a circular or parabolic cross-sectional shape. The range of angles is determined by the properties of the light guide material in connection with internal reflection in the material.

The exit region may be provided with a frosted or rippled surface. The ripples can be arranged perpendicular to the longitudinal axis of the mirror in order to spread the light in the direction parallel to the, for example cylindrical, mirror. However, ripples may also be provided in other directions in order to adjust the light distribution. Furthermore, the exit region may be provided with a coating configured to diffuse, dye, filter, or refract light.

In an advantageous embodiment, the lamp module according to the invention comprises a housing enclosing the light source and the light guide with mirror. Such a housing may be configured for interconnection to other lamp modules of the same kind.

In accordance with the introduction, the invention also foresees a shelf system with at least two shelves arranged above each other, the underside of the upper shelf being provided with at least one lamp module according to the invention, the lamp module being provided with the exit region directed downwards for illumination of the shelf below. The module may advantageously be mounted, for example by using adhesive tape, underneath a shelf near the front part of that shelf, thus illuminating the shelf below and any objects on it. LEDs require low voltage and have very low energy consumption, allowing thin wires to be used for the power supply and requiring only a very small hole in the back of the bookcase or cabinet for the cable.

Brief description of the drawings

Figure 1 is a side view of a lamp module according to the invention with a convex mirror, Figure 2 is an alternative embodiment with a concave mirror

Figure 3 is a bottom view of an LED light source and the light guide.

Figure 4 is a side view of a CCFL light source, a reflector and the light guide.

Figure 5 is a bottom view of lamp modules capable of interconnecting,

Figure 6 is an illustration of a shelf system with a lamp module according to the in- vention, Figure 7 shows a bent light guide using a mirror at the bend,

Figure 8 shows a bent light guide using a mirror at the bend and an exit region pointing the opposite way,

Figure 9 shows a bent light guide with two light entrances and one exit region using two mirrors to bend and combine the fans of light,

Figure 10 shows a bent light guide using two low angle surfaces for internal reflection, Figure 11 shows a bent light guide using a soft curve for internal reflection, Figure 12 is a side view of a light guide with a combined concave and convex mirror, Figure 13 is a front view of a rod shaped light guide with a combined concave and convex mirror.

Detailed description of the invention

The lamp module 14 in a first embodiment is shown in FIG. 1. The lamp module 14 includes at least one miniature light source 1 with very low heat dissipation, preferably an LED. Though the invention will be explained with one light source per lamp module 14, it is implicit that a number of light sources 1 may be arranged for each lamp module 14.

The light source 1 is mounted near the rear surface 12 of a light guide 15 such that the emitted light is mainly directed towards the front end 13 of the light guide 15 where the reflector 3 a is located. In the near vicinity of the light source 1, emitted light will enter into the light guide 15 made of optically clear material, preferably acrylic polymer (Polymethyl-methacrylate, PMMA) or glass. The rear surface 12 of the light guide 15 facing the light source 1 is shaped as a convex cylindrical lens 2 with an axis parallel to the reflector 3 a and a curvature adapted to the distance to the light source 1 in order to create a light beam 16 in the light guide 15 which propagates mainly as parallel fans of rays from the rear of the module 15 to the front end reflector 3 a. Light beams slightly off the parallel path 16 will be reflected by internal reflection insight the light guide at the planes 4 between the rear end 12 and the front 13 of the module

14.

Due to refraction during entrance into the module at the rear end 12, the horizontally diverging light from the light source 1 entering the module 14 as parallel fans of rays is redirected slightly into a more forward direction decreasing the angular divergence of the fans of rays. This decrease can be counteracted, as illustrated in FIG. 3, by providing a concave curve 6 at the rear end 12 of the light guide 15, where the radius of curvature of the curve 6 has its origin at a focal point of the light source 1. Using a radius of curvature less than the distance to the focus of the light source 1, will results in an enhanced spreading the fans of rays inside the module 15.

The front end 13 of the light guide 15 may be provided with a concave cylindrical mirror 3 a with an axis parallel with the front of the lamp, as shown in FIG. 1. Alternatively, the reflector may be a convex mirror, as illustrated in FIG. 2. The reflector 3 a, 3b, reflects light out of the module 15 with a certain angular divergence, for example between 65 and 115 degrees as measured from the exit surface 5 in the plane 4. When light emits through the exit surface 5 of the light guide 15, it will undergo refraction and leave the light guide 15 in a changed angular divergence, for example at angles between 45 and 135 degrees. For a general purpose lamp of this type, emitting angles between 45 and 90 degrees are typically desirable. For special purposes it may be desirable to use the maximum interval of angles or any predetermined fraction thereof. The characteristics of the curved mirror 3 a, 3b determines the range of emitting angles.

Part of the bottom surface 4 of the light guide 5 may be frosted to diffuse the light beam or rippled to enhance sideways refraction of the light, the latter being advantageous, if the diverging fan of rays has a relatively little degree of divergence. Alternatively, the surface 5 or part thereof may be coated with a substance being able to diffuse, dye, filter, refract light as required for different purposes.

The light source 1, the necessary electronic circuitry and parts of the light guide 15 may be enclosed in a housing 10 that hides the circuitry, protects the light guide and cuts off any stray light. The housing 10 may comprise connectors for power supply on the rear.

In a further embodiment of the invention, sockets may be provided for mounting several lamp modules 14 together, for example by interconnecting the electrical circuitry by means of suitable pin headers. To stabilise the joint, the housing may be provided with one or more holes 17 facing corresponding holes in the next module 14 providing the opportunity to fit the holes 17 with a pin 11 holding the modules 14 in place, as illustrated in FIG. 5. The modules 14 can be connected in a row, numbers limited only by the ability of the circuitry to provide sufficient power for all units. The row may even be continued without interconnecting the circuitry because any one of the modules 14 in a row may be connected by cable to the power supply.

As means for affixing the lamp modules 14 to the underside of a shelf, each module will be fitted on the surface with one or more strips of self adhesive tape. Similar tape will be used to affix power supply cables completely eliminating the need for nails or screws.

The lamp module may be mounted vertically, for example for side illumination of signs, shelves or doors, upside down, for example for illumination of steps in stairs from below, or in any other position suitable for proper illumination in a given environment.

CCFL tubes 9, as illustrated in FIG. 4, can be used as an alternative light source 1 in stead of LEDs. Whereas LEDs emit light in a specific and often very limited direction,

CCFL tubes emit light in all directions. This calls for a reflector 8 surrounding those parts of the tube not facing the light guide 15, and it renders the lens provided by the curved rear surface superfluous, such that the rear end 12 may be provided as a straight edge 7.

Whether the light source be LEDs or CCFLs, it will be necessary to supply the lamps with regulated power suitable for the chosen light source. Circuitry for that purpose will be embodied in a box placed anywhere behind, beside or above the bookcase or cupboard. The box may have out takes for several rows of lamp modules. The box may have a build in transformer enabling it to take power directly from the wall outlet, or it may take in low voltage power from a commercial plug in type transformer.

A shelf system is illustrated in FIG. 6 comprising an upper shelf 20 and a lower shelf

21 as seen from the side. The upper shelf 20 is equipped with a lamp module 14 ac- cording to the invention at the underside near the front part of the shelf 21. The mod- ule provides illumination 22 of the lower shelf, the illumination directed downwards within an angular span of between 90°, i.e. vertically down, and a certain angle v, which is to be determined in accordance with the desired illumination properties in dependence of the dimensions of the shelf system. For example, the depth of the shelves may be assumed 0.3 m, whereas the distance between the shelves is 0.3 m.

Thus, the angle v should be arctg 0.3/0.3 = 45°.

In order to exit the light guide through the exit region at an angle of v=45°, see FIG. 1 for illustration, the angle inside the light guide can be calculated by using Snell's law yielding v'= 90° - arcsin (sin (90°-v)/n), where n is the index of refraction of the light guide material, for example 1.5. Thus, the angle v' inside the light guide would be 62°. In order to reflect into angles between 62° and 90° at the mirror surface, assuming parallel beam incidence, the tangent of the mirror should vary between w=90°+62 2=122° and w'=90°+9072=135°. Having this in mind, a bending surface may be arranged, for example a surface with a circular bending. A circular bending would, however, not result in a homogeneous illumination of the shelf below, but a lower intensity would be experienced towards the back part of the shelf. For a more homogeneous bending, the curvature should vary with a tangent with a slope between 122° and 135° but in a more flat manner around 122°, for example by using a concave parabolic surface with increasing bending from the upper part with 122° tangent to the lower part with 135° tangent.

In principle, it is also possible to use other kind of curves than smooth curves for the mirror, for example a curve resulting from linear pieces with different slopes, or with steps. However, a smoothly reflecting surface is preferred, as the production is very easy and the provision of the mirror is simple, for example by providing a reflective metal foil glued on the prepared smoothly curving surface, for instance as a tape.

In case that the distance between the shelves is less than the depth, it should be born in mind that internal reflection may occur for rays at smaller angles v\

In order to optimise the light guiding properties, it is possible to coat the planes and sides of the light guide with a reflective material. However, in most cases, this is not necessary. Typical dimensions of a light guide in a lamp module according to the invention is a height of 5.5 mm, a width of 135 mm and a length from rear to front of 20 mm. The height should be larger than the height of the light source. For example, an used LED had a diameter of 5 mm and an angular light divergence of +/- 10° (viewing angle of 20 degrees). A housing has been successfully constructed with outer dimensions 7 mm x 145 mm x 40 mm.

The planes of the light guide may be planar and parallel. However, other configurations are possible, for example non-parallel planes, resulting in a wedge-shaped light guide, or planes that are not planar but bent or otherwise curved.

Fig. 7 - 11 show different examples of bent or curved light guides. As illustrated in Fig. 7-9, a sharp bend can be achieved using a reflective surface 23 acting as a mirror. As illustrated in Fig. 10, a smooth bend can be achieved using two or more plane sur- faces 24 arranged to reflect the light in steps around the bend by internal reflection.

For that purpose the angle U must not exceed the maximum angle of internal reflection (e.g. 41.8°) for the material in use. As illustrated in Fig. 11, a smooth bend can also be achieved using a smooth curve 25 in which the angle U at no point exceeds the maximum angle of internal reflection, and preferably in which reflection from the in- ner curve 26 is avoided. However, using a smooth curve will not provide parallel beams of light 16 inside the light guide. Light will leave the exit region in more dispersed angles than intended leading to a less efficient utilization of the light available. A combination of bends, as shown in Fig. 9 can be used to couple two or more light sources to one light guide in order to provide higher luminous intensity from the exit region.

Fig. 12 shows an embodiment in which the upper half 27 of the mirror 3 c is concave and the lower half 28 is convex. This shape is very advantageous when used in a cylindrical light guide, shown as a front view in Fig. 13, where it makes it possible to emit all the light evenly in a semicircle 29. Assuming an even distribution of light inside the light guide, this construction will provide a higher luminous intensity at angles reflected from those parts of the mirror that are closest to the cylindrical edge of the light guide. This effect can be used to compensate for the dispersion of light as a function of distance thus approximating an even distribution of light on the surface covered by the semicircle 29. A light guide of this type would be suitable for illumina- tion of paintings, signs etc. Various dimensions may be applied for a lamp module according to the invention for optimising and adaptation to the desired conditions and optical appearance.

Applications of the invention include illumination of cabinets, signs, pictures, displays, exhibition cases, staircases, toys and aquaria, the list in no way being exclusive. However, the use of light guides for communication purposes or medical application is considered outside the scope of this invention.

Claims

1. A lamp module having a light guide with a rear end and a front end and a side surface between the rear end and the front end, the module further comprising at least one light source optically coupled to the rear end of the light guide, the front end of the light guide being provided with a reflective surface for reflecting light from the light source after propagation through the light guide, wherein the reflective surface is a mirror configured to reflect light from the light source through an exit region in the side surface.

2. A lamp module according to claim 1, wherein the reflective surface is smoothly curved.

3. A lamp module according to claim 1 or 2, wherein the light source is a Light Emit- ting Diode.

4. A lamp module according to claim 3, wherein the optical coupling between the light source and the light guide comprises a curved rear end of the light guide constituting a cylindrical lens for transforming divergent light rays from the light source into parallel fans of rays inside the light guide.

5. A lamp module according to claim 1, 2 or 3, wherein the optical coupling between the light source and the light guide comprises a double-curved rear end, the curvature of which is convex in a first direction for transforming divergent light rays from the light source into parallel fans of rays inside the light guide, and concave in a perpendicular direction in order to increase the spread of the fans of rays inside the light guide.

6. A lamp module according to claim 1 or 2, wherein the light source is a Cold Cath- ode Fluorescent Lighting tube and wherein the optical coupling between the light source and the light guide comprises a reflector (8) surrounding those parts of the light source not facing the light guide.

7. A lamp module according to any of the preceding claims, wherein the curved mirror is convex or concave with a reflecting surface having a circular or parabolic shape.

8. A lamp module according to claim 7, wherein the mirror is configured to reflect the light from the light source into angles between 40 and 140 degrees outside the exit surface of the light guide.

9. A lamp module according to any of the preceding claims, wherein the exit region is provided with a frosted or rippled surface.

10. A lamp module according to any of the preceding claims, wherein the exit region is provided with a coating configured to diffuse, dye, filter, or refract light.

11. A lamp module comprising a housing embodying or enclosing the light source and the light guide with mirror, the housing being configured for interconnection to other lamp modules of the same kind.

12. A shelf system with a least two shelves arranged above each other, the underside of the upper shelf being provided with at least one lamp module according to any of the preceding claims, the lamp module being provided with the exit region directed downwards for illumination of the shelf below.

13. Use of a lamp module according to claims 1-10 for a shelf system, a cabinet, a sign, a picture, a display, an exhibition case, a staircase, a toy, or an aquarium.