GB2340215A

GB2340215A - Scattering illumination light source

Info

Publication number: GB2340215A
Application number: GB9917368A
Authority: GB
Inventors: Keith Anderson; Geoffrey Archenhold; Kurt Baldwin; Andrew Neal
Original assignee: Integrated Systems Technologies Ltd
Current assignee: Integrated Systems Technologies Ltd
Priority date: 1998-07-30
Filing date: 1999-07-26
Publication date: 2000-02-16
Anticipated expiration: 2019-07-26
Also published as: GB9917368D0; GB2340215B; GB9816492D0

Description

2340215 Scattering Illumination Light Source This invention relates to

light sources, especially those applied to lurninaire systems. It is particularly useful providing a uniform illumination source whose luminosity can be controlled, or for coupling light into one or a plurality of optic fibres.

The aim of any light source is to collect as much light as possible that is emitted from a bulb, and to direct this light into the chosen direction. This has traditionally been achieved using a reflector behind the bulb to collect the fight that is emitted back-wards or sideways, and to reflect this fight into a forward direction. The reflector is acting as an imaging optic, providing a (blurred) image of the bulb filament in the forward direction.

The 11-ht source described in t1iis invention does not imasie the bulb filament, but scatters the emitted light within a chamber. The chamber is arranged to have an exit means for the scattered lmht to escape, and thus provide an output. The principle is similar to that used for integrating spheres. Here a light source is placed inside a sphere whose interior is coated with an efficient reflective or scattering material. Typical efficiencies are >99% for the incident light being reflected or scattered, which means that very little light is absorbed by the inside surface of the sphere. The light emitted from the light source is thus scattered many times within the sphere, effectively randomising the direction of travel of the photons. Any particular portion of the inside of the sphere W-111 have the same light power incident upon it. When a small light detector is placed at the surface of the sphere, the reading on the detector will be proportional to the total amount of light emitted from the source, independent of the direction that it was emitted in. This type of photometric analysis is the usual application of these devices.

The application described within this invention is to use an efficiently scatterin--/reflectina chamber surrounding a light source. A hole in the side of the chamber will emit a uniform light intensity, independent upon the directional properties of an errussion light bulb or source within the chamber. This is therefore a non-imaging light source - any information about the spatial distribution of the light emission is removed by the multiple scattering events as the photons pass across the inside of the chamber.

According to the present invention, there is provided a light source comprisin& a fight source-, a scattering chamber surrounding the fight source; a exit port in the chamber which provides for the light output.

Specific embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, wherein.- Figure I is a schematic diagram of the system consisting of a light source, scattering chamber and exit port geometry for controlling the light output; Figure 2 is a schematic diagram of a method for controlling the light intensity by a mechanical means.

Figure 3 is a diagram of a design of an intemal'colfintinating' tube which can increase the output light level by recollecting some of the undesirable rays of light.

Figure 4 is a diagram of a design of an external 'collimating' tube', Figure 5 is a diagram of the system with the light source mounted axially, and with a mirrored cone obscuring the direct path of rays from the light source to the exit hole.

Figure 6 is a diagram of the system with optical fibres at the output-, Figure 7 is a diagram of the system with the ends of optical fibres positioned in the vicinity of the wall of the scattering chamber- Flo-,ure 8 is a dia-ram of the output system with optical fibres, ball lenses, and alignment balls; Flaure 9 is a different View of the output system of figure 8, showing a packing arranaement of the balls and optic fibres; Flaure 10 is a dla--ram of the systern with a'hot mirror' to remove some of the -3 infrared heat; Figure 11 is a diagram of the system with a light source powered using microwave radiation through a window in the chamber wall; and Figure 12 is a diagram of the system with a plurality of light sources. Referring to the drawings, the system shown in figure I has a light source I located inside a chamber 2, which is coated with an efficient scattering surface. This chamber is similar to an integrating sphere. The chamber has an exit port -3) which provides the light output, which in the case of a luminaire is directed towards a gate 6. The distribution of light intensity, and the collimination of the light can be controlled using a tube positioned inside the chamber 4 or outside the chamber 5.

The degree of collimination of the light emitted from the chamber will depend upon the ratio of the tube 4, 5 length to diameter. The tube must not extend too far into the chamber so that it shadows the chamber wall in region 12 which is the surface emitting light towards the exit hole 3 of the chamber. The outside of the tube should be coated with an efficient reflection/scattering material so that it acts like a part of the internal wall of the chamber and therefore does not absorb the photon energy within the chamber.

The preferred location of the light source 1 is for it to be positioned in the chamber so that there is no path for the light emitted from the light source to the exit port 3) of the chamber. If there were a direct path, then the light emitted from the chamber Would no longer have a uniform spatial distribution. One such position is shown in figure 1.

The output intensity of a light system is usually controlled by adjusting the electrical po,A,er feed to the light source (bulb). This requires additional electronics to be able to provide this level of control. The use of the scattering chamber light source means that the output level can be controlled by a mechanical means, such as a shutter, which phNsically covers the 112ht source. This could not be performed usino a conventional reflector/condenser arranoement because the edae of the shutter would form an image over 4- the exit gate. This non-imaging source arrangement does not image the local fight source, and so can still provide a uniform light level across the exit, independent of the amount of the local light source that is covered by a shutter. This is illustrated by way of two example embodiments in figure 2. The upper diagram shows a cross section of a sliding dome cover 8 over the light source 1. The lower figure shows a cylindrical cover 7 which can be moved to fully enclose the light source using an end cover. The mechanical shutter can be controlled, for example using a simple motor (stepper or DQ and simple electronics, or manually using some mechanical attachment to the outside of the system. Thus the system negates the need for complicated dimming electronics.

If an internal tube 4 was used to control the collimination of the fight output, then this could be designed with slats to collect some of the tight that is incident on the entrance of the tube, but would miss the exit hole. This is illustrated in cross section in figure 3). The rays of light 9 that are transn-Litted by the slatted tube pass back into the bulk of the chamber to undergo more scattering, processes. The use of the slatted tube would therefore increase the overall light output intensity because it reduces the amount of absorption surfaces (if for example the inside of the tube 4 was an absorption surface), or unwanted output rays of fight from within the system (if for example the ray of light 9 were reflected off the tube 4, it would propagate through the exit hole of the chamber at a steep angle).

An external tube 5 can also be used to control the degree of collimation of the output, as illustrated in figure 4. If an external tube was used without an internal tube, then the use of slats in the tube would not increase the light level as described for the internal tube becausetheTays of light escaping through the slats would be lost from the system. However, it may be advantageous to make the inside of the external tube into a rru'rror-like surface. The rays of light 10 that are incident on the external tube will be at a grazin 9 angle, especially if the external tube is used in conjunction with an internal tube. This means that the reflection from the internal surface of the external tube V.11111 help to concentrate the fight into the required region (external gate 6, figure 1).

The whole fight source system may be made axially symmetric, as illustrated in figure 5. This may have some advantages with manufacture. A mirror or scattering cone I I could be used to shield the exit port 3 from a direct fine of sight of the light source 1. The output light would come from the vicinity of the lateral circumference of the chamber 2, via a reflection off the mirror or scattering surface 11.

The scattering chamber system would also provide an efficient means of coupling light from the light source I into one, or a plurality, of optic fibres 13, as illustrated by figure 6. The fibres can be positioned anywhere in the output path of the chamber. Figure 6 shows the fibres at the end of an external tube 5. The use of tubes 4,5 would help to control the range of angle of the light incident upon the ends of the fibres, hence controlling the efficiency of coupling light into the fibres (which will have a limited acceptance angle). The fibres could also be positioned such that their ends are in the vicinity of the wall of the chamber, as shown in figure 7. This configuration has the advantage of simplicity over that shown in figure 6.

The light can also be focused into the fibres using ball lenses. An embodiment of this system is shown in figure 8. Ball lenses 14 are transparent spheres which act to couple light from an external source into the optic fibre 13. A potential problem with this arrangement is ahmine the ball lenses 13 with the ends of the optic fibres. This can be aided using a second layer of spheres 15 (eg ball bearings), which would stack over the interstitial re2ions of the ball lenses, thus providing a location pocket for the optic fibres. This is also illustrated in a different projection in figure 9, for the case of a cubic packing arrancrement. There are many packing arrangements (which are well known from D crystal I o graphy), including hexagonal close packing which has a larger packing densitv I ID C I-D I than the cubic arrangement shown. The schematic diagram of fi--ure 9 shows the case with the optic fibre D being smaller in diameter than the ball bearing 15. The packing principle would work as well if the fibre had a lareer diameter than the alignment bearing, or if they were of sin-dlar diameter.

A potential problem with many luminaire systems is the removal of the heat ermitted ftom the light source 1. Since this system is a relatively enclosed system around the fight source, this is a matter that requires some attention. The use of efficient light sources (such as the Philips. Alfastercolour CDM- T bulb) would be especially applicable with this invention. However, a window could be incorporated into the wall of the chamber, as illustrated in figure 10. If this window had a reflection/transrm'ssion characterli stic that efficiently reflected visible radiation, but transnuitted in&a red radiation (heat), then this would help to reduce any build-up of heat within the chamber.

A window could also be introduced into the output path from the chamber. If this window had a reflection/transmission characteristic that efficiently transmitted visible licht and reflected infra red radiation (heat), then this would help to reduce the heat at the output of the system.

This scattering chamber could also be used with other types of Eght sources. For example fiaure I I shows a sulphur lamp 18 inside the chamber, which may need to have a special window 17 in the wall of the chamber to transrru't microwave radiation to power the lamp.

The material for the interior coating, of the chamber needs to have a minlimal absorption of the incident 11!aht. It therefore needs to be especially efficient at either scattering or reflectina licaht. One material that is suitable for this is glass powder, with a particle size of less than approximately 10 pm. This powder could be fixed to the inside wall of the chamber usina an adhesive or other type of cement, or it could be mixed in a paint, resin, or some other carrier, which is either coated onto the inside of the chamber, or makes up the structure of chamber.

There are many applications for this type of light source system. Some of these applications include luminaires for stage or theatre lighting, or architectural illumination, sources for video projection (liquid crystal display panels, digital mirror device projections) and for illuminating light guides (optic fibres, transparent codults).

The system can consist of one or a plurality of light sources and emitters 19, such as:- a) Fluorescent light, linear and compact.

b) Halogen incandescent lamps.

c) Incandescent light bulbs.

d) Tungsten filament lamps.

e) High intensity discharge lamps, (HID) f) Light emitting diodes (LEDs) all/different colours.

g) Electro luminescent lamps.

h) Radioluminescent lamps.

i) Radiofrequency (RF) lamps.

D Microwave light sources.

k) Laser light sources.

The output intensity of the light source(s) can be controlled by means of mechanical, electrical and electronic systems.

Claims

8 CLAIMS

1 Apparatus comprising a light source, a chamber surrounding the light source, the chamber having an inner surface for scattering and/or reflecting light from the light source, and an exit port in the chamber which provides for a light output, the arrangement being such that there is no direct path for light emitted from the light source to the exit port..

2. Apparatus according to claim 1 wherein the light source comprises 10 one or more light emitters within the chamber.

3. Apparatus according to claim 1 or claim 2 wherein the chamber is provided with means for collimating the light output.

4. Apparatus according to claim 3 wherein the collimating means is provided at the exit port and comprises a tube extending into the chamber.

5. Apparatus according to claim 4 wherein the tube has an outer surface for scattering and/or reflecting light incident on the outer surface It, )0 within the chamber.

6. Apparatus according to claim 4 wherein the tube has an inner surface adapted to transmit light incident on the inner surface for further scattering and/or reflection within the chamber. 25 7. Apparatus according to claim 6 wherein the tube is formed with inclined slats providing openings for transmitting light incident on the inner surface.

9 8. Apparatus according to claim 4 wherein the collimating means comprises a tube extending out of the chamber.

9. Apparatus according to claim 8 wherein the tube has an inner 5 surface for reflecting light incident on the inner surface.

10. Apparatus according to claim 9 wherein the inner surface is a mirrorlike surface.

11. Apparatus according to any one of the preceding claims wherein optic fibres are provided for collecting the light output for fibre lighting.

12. Apparatus according to claim 11 wherein means is provided for focusing the light output into the optic fibres.

13. Apparatus according to claim 12 wherein the focusing means comprises ball lenses.

14. Apparatus according to claim 13 wherein means is provided for 20 aligning the ball lenses with the ends of the optic fibres.

15. Apparatus according to claim 14 wherein the alignment means comprises spacers between the optic fibres forming pockets for locating the ball lenses.

16. Apparatus according to any one of the preceding claims wherein the chamber is provided with means for reducing heat build-up within the chamber.

17. Apparatus according to claim 16 wherein the chamber heat reduction means comprises a window having a reflection/transmission characteristic for reflecting visible radiation back into the chamber and transmitting infra-red radiation from the chamber.

Apparatus according to claim 17 wherein the window is provided in a wall of the chamber.

19. Apparatus according to any one of the preceding claims wherein the chamber is provided with means for reducing heat build-up at the light output.

20. Apparatus according to claim 19 wherein the light output heat reduction means comprises a window in the light output path for transmitting visible light and reflecting infra-red radiation.

21. Apparatus according to any one of the preceding claims wherein means is provided for varying the light output intensity.

22. Apparatus according to claim 21 wherein the light output intensity varying means comprises an adjustable shutter or cover for the light source.

23. Apparatus according to claim 22 wherein the shutter or cover is 25 controlled bv a motor or manually.

24. Apparatus accordinc, to anv one of the preceding claims wherein licrht from the licht source is scattered and/or reflected by class powder on the inner surface of the chamber.

11 25. Apparatus according to claim 24 wherein the glass powder has a particle size of less than 10 microns approximately.

26. Apparatus according to any one of the preceding claims wherein the light source is offset relative to the exit port.

27. Apparatus according to any one of claims 1 to 25 %%,herein the light source is aligned with the exit port and is shielded from the exit port.

28. Apparatus according to any one of the preceding claims wherein the light intensity from the light source is controlled by mechanical, electrical or electronic means either separately or in any combination.

29. A lighting system comprising a light source, a chamber surrounding the light source, the chamber having an inner surface for scattering and/or reflecting light from the light source, and an exit port in the chamber providing a light output from the chamber, the light source and exit port being arranged and/or adapted so that light from the light source is scattered and/or reflected within the chamber prior to passing out of the chamber through the exit port.

30. Light source comprising a light emitter located inside a chamber whose inner surface is an efficient optical scatterer or reflector, and a port in the chamber which acts as the output means of the light source, the light emitter within the chamber being shielded from direct line of sight from the port either by use of baffles or shields A,,ithin the chamber, and/or by the geometry of the chamber.

31. Apparatus substantially as hereinbefore described vvith reference to Fioure 1 of the accompanying drawings.

12 32. Apparatus substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings as modified by any one of Figures 2 to 12 of the accompanying drawings. 5