Non-imaging light source for uniform illumination applications

[0002] This invention relates to light sources, especially those applied to luminaire systems. It is particularly useful in providing a uniform illumination source whose luminosity can be controlled, or for coupling light into one or a plurality of optic fibres.

[0003] 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 light that is emitted backwards or sideways, and to reflect this light into a forward direction. The reflector is acting as an imaging optic, providing a (blurred) image of the bulb filament in the forward direction.

[0004] The light source described in this invention does not image the bulb filament, but scatters the emitted light within a chamber. The chamber is arranged to have an exit means for the scattered light 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 will 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.

[0005] It is an object of this invention to use an efficient scattering chamber as a uniform illumination light source.

[0006] According to the present invention, there is provided apparatus comprising:

[0007] a light source;

[0008] a scattering chamber having an internal surface for scattering light from the light source; and

[0009] an exit port in the chamber which provides a light output.

[0010] By this invention, the exit port emits a uniform light intensity, independent upon the directional properties of the light source, e.g. an emission light bulb. In other words, a non-imaging light source is provided in which any information about the spatial distribution of the light emission is removed by multiple scattering events as the photons pass across the inside of the chamber.

[0011] The light source can be any of the following:

[0012] a) Fluorescent light, linear and compact

[0013] b) Halogen incandescent lamps

[0014] c) Incandescent light bulbs

[0015] d) Tungsten filament lamps

[0016] e) High intensity discharge (HID) lamps

[0017] f) Light emitting diodes (LEDs) all/different colours

[0018] g) Electroluminescent lamps

[0019] h) Radioluminescent lamps

[0020] i) Radiofrequency (RF) lamps

[0021] j) Microwave light sources

[0022] k) Laser light sources

[0023] The light source may consist of one or more light emitters positioned internally and/or externally of the chamber. Where more than one emitter is provided, these may be the same or different. Where an external emitter is provided, the chamber has an entrance port for light to enter the chamber. More than one entrance port may be provided.

[0024] The chamber may be adapted to reduce heat build-up within the chamber and/or in the light output at the exit port. For example, one or more windows may be provided with reflective/transmissive properties for separating visible light and infrared radiation (heat). Thus a window may be provided in the chamber wall to transmit infrared radiation out of the chamber and reflect visible light within the chamber and/or a window may be provided in the exit port to transmit visible light out of the chamber and reflect infrared radiation within the chamber.

[0025] The intensity of the light output may be controlled by varying the intensity of the light source. This may be achieved by mechanical, electrical or electronic systems. A mechanical system may employ an adjustable shutter for covering the light source. This is particularly simple and can take various forms, for example, a sliding cover or an iris diaphragm. More than one exit port may be provided.

[0026] Specific embodiments of the invention will now be described by way of example, with reference to the accompanying drawings.

[0027] FIG. 1 is a schematic diagram of the system consisting of an internal light source, scattering chamber and exit port geometry for controlling the light output;

[0028] FIGS. 2A and 2B are schematic diagrams of methods for controlling the light intensity by mechanical means;

[0029] FIG. 3 is a schematic diagram of a design of an internal portion of a colliminating tube which can increase the output light level by recollecting some of the undesirable rays of light;

[0030] FIG. 4 is a schematic diagram of a design of an external portion of a collimating tube;

[0031] FIG. 5 is a schematic 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 port;

[0032] FIG. 6 is a schematic diagram of the system with optical fibres at the output;

[0033] FIG. 7 is a schematic diagram of the system with the ends of optical fibres positioned in the vicinity of the wall of the scattering chamber;

[0034] FIG. 8 is a schematic diagram of the output system with optical fibres, ball lenses, and alignment balls;

[0035] FIG. 9 is a different view of the output system of FIG. 8, showing a packing arrangement of the balls and optic fibres;

[0036] FIG. 10 is a schematic diagram of the system with mirrors to remove some of the infrared heat;

[0037] FIG. 11 is a schematic diagram of the system with a light source powered using microwave radiation through a window in the chamber wall;

[0038] FIG. 12 is a schematic diagram of the system with a plurality of light sources;

[0039] FIGS. 13A and 13B are schematic diagrams of systems with an external light source;

[0040] FIG. 14 is a schematic diagram of the system with a reflective video projection device and projection optics at the exit port to provide static or moving image projections; and

[0041] FIG. 15 is a schematic diagram of the system with a transmissive video projection device and projection optics at the exit port to provide static or moving image projections.

[0042] Referring to the drawings, the system shown in FIG. 1 has a light source 1 located inside a chamber 2 having an internal surface which is an efficient light scatterer. This chamber is similar to an integrating sphere.

[0043] The chamber 2 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 4 for the exit port 3. The tube 4 may have an internal portion 4′ and/or an external portion 4′.

[0044] The degree of collimation of the light emitted from the chamber 2 will depend upon the ratio of the length of tube 4 to the diameter of tube 4. The tube 4 must not extend too far into the chamber 2 so that it shadows the chamber wall in region 12 which is the surface emitting light towards the exit port 3 of the chamber. The outside of the tube 4 should be an efficient light scatterer so that it acts like a part of the internal surface of the chamber 2 and therefore does not absorb the photon energy within the chamber.

[0045] The preferred location of the light source 1 is for it to be positioned in the chamber 2 so that there is no direct path for the light emitted from the light source 1 to the exit port 3 of the chamber 2. One such position is shown in FIG. 1. If there were a direct path, then the light emitted from the chamber 2 would no longer have a uniform spatial distribution.

[0046] The output intensity of a light system is usually controlled by adjusting the electrical power feed to the light source (bulb). This requires additional electronics to be able to provide this level of control.

[0047] 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 physically covers the light source. This could not be performed using a conventional reflector/condenser arrangement because the edge of the shutter would form an image over the exit gate. This non-imaging source arrangement does not image the local light 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 FIGS. 2A and 2B.

[0048] FIG. 2A shows a cross section of a sliding dome cover 8 over the light source 1. FIG. 2B shows a cylindrical cover 7 which can be moved to fully enclose the light source 1 using an end cover. The mechanical shutter can be controlled, for example using a simple motor (stepper or DC) 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.

[0049] As shown in FIG. 3, an internal portion of a colliminating tube 4acan be designed with slats 5 to transmit some of the light that is incident on the inside of the tube 4a.The rays of light 9 that are transmitted by the slats 5 pass back into the bulk of the chamber 2ato undergo more scattering processes. The use of the slats 5 would therefore increase the overall light output intensity because it reduces the amount of absorption surfaces (if for example the inside of the tube 4awas an absorption surface), or unwanted output rays of light from within the system (if for example the ray of light 9 were reflected off the tube 4a,it would propagate through the exit port 3 of the chamber 2aat a steep angle).

[0050] An external portion of a colliminating tube 4bcan also be used to control the degree of collimation of the output, as illustrated in FIG. 4. Slats in the external portion of tube 4bwould not increase the light level as described above for the internal portion of the tube 4abecause the rays of light escaping through such slats in external portion would be lost from the system. However, it may be advantageous to make the inside of the external portion into a mirror-like surface. The rays of light 10 that are incident on the inside of the external portion will be at a grazing angle, especially if the external portion is used in conjunction with an internal portion. This means that the reflection from the internal surface of the external portion will help to concentrate the light into the required region (e.g., the external gate 6 shown in FIG. 1).

[0051] The whole light source system may be made axially symmetric, as illustrated in FIG. 5. This may have some advantages with manufacture. A mirror or scattering cone 11 could be used to shield the exit port 3 from a direct line of sight of the light source 1. The output light would come from the vicinity of the lateral circumference of a chamber 2bvia a reflection off the mirror or scattering cone 11.

[0052] The scattering chamber system can also provide an efficient means of coupling light from the light source 1 into one, or a plurality, of optic fibres 13, as illustrated by FIG. 6. The fibres 13 can be positioned anywhere in the output path of the chamber 2. FIG. 6 shows the fibres at the end of the external portion 4″. The use of the tube 4 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 13 could also be positioned such that their ends are in the vicinity of the wall of the chamber, as sown in FIG. 7. This configuration has the advantage of simplicity over that shown in FIG. 6.

[0053] The light can also be focused into the fibres 13 using ball lenses. An embodiment of this system is shown in FIG. 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 aligning the ball lenses 14 with the ends of the optic fibres. This can be aided using a second layer of spheres 15 (e.g. ball bearings), which would stack over the interstitial regions of the ball lenses 14, thus providing a location pocket for the optic fibres. This is also illustrated in a different projection in FIG. 9, for the case of a cubic packing arrangement. There are many packing arrangements (which are well known from crystallography), including hexagonal close packing which has a larger packing density than the cubic arrangement shown. The schematic diagram of FIG. 9 shows the case with the optic fibre 13 being smaller in diameter than the spheres 15. The packing principle would work as well if the fibre had a larger diameter than the alignment bearing, or if they were of similar diameter.

[0054] A potential problem with many luminaire systems is the removal of the heat emitted from the light source 1. Since the system described thus far is a relatively enclosed system housing the light source 1 within a chamber, this is a matter that requires some attention. To this end, a window 16 can be incorporated into the wall of a chamber 2c,as illustrated in FIG. 10 having a reflection/transmission characteristic that efficiently reflects visible radiation, but transmits infra red radiation (heat) thereby helping to reduce any build-up of heat within the chamber.

[0055] Alternatively or additionally, a window 17 can be introduced into the output path from the chamber 2cas also illustrated in FIG. 10 having a reflection/transmission characteristic that efficiently transmits visible light and reflects infra red radiation (heat) so as to help to reduce the heat at the output of the system.

[0056] The use of efficient light sources (such as the Philips Mastercolour CDM-T bulb) would be especially applicable with this invention. However, other types of light sources can be used. For example, FIG. 11 shows a sulphur lamp 19 inside a chamber 2d,which has a window 18 to transmit microwave radiation to power the lamp 19.

[0057] The light source may comprise a plurality of emitters. For example, FIG. 12 shows a light source 20 consisting of three emitters within a chamber 2e.In another modification (not shown), a chamber surrounding light source 1 can have a plurality of exit ports.

[0058] The system can also be used where very high intensity light sources are required. In this case, it may be preferable to position the light source outside the chamber. FIGS. 13A and 13B show two arrangements with an external light source 1 and a collector 21 for directing light from the light source 1 towards an entrance port 22 in the wall of a chamber 2f.

[0059] The port 22 could have a reflection/transmission characteristic that transmits visible light into the chamber 2fand reflects infrared radiation (heat) to prevent heat build-up within the chamber 2f.

[0060] Alternatively and/or additionally, the collector 21 could have a reflection/transmission characteristic that reflects visible light towards the entrance port 22 and transmits infrared radiation (heat) out of system to reduce heat build-up within the chamber 2f.

[0061] The use of an external light source enables the light intensity at the exit port 3 to be controlled mechanically. FIGS. 13A and 13B show two arrangements for this using a sliding cover 23 (FIG. 13A) and an iris diaphragm 24 (FIG. 13B) to vary the size of the entrance port 22 exposed to the light source 1.

[0062] The material for the interior coating of the chamber and, where provided, external coating of the internal portion of the colliminating tube, needs to have a minimal absorption of the incident light and to be especially efficient at scattering light. We prefer to use scattering materials having an absorption of less than 5% and more preferably less than 1%.

[0063] One material found to be particularly suitable for this is glass powder with a particle size of less than approximately 10 μm. This powder can be fixed to the inside wall of the chamber using 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. Other scattering materials that may be used include barium sulphate or heat resistant matt white paint.

[0064] The scattering materials employed in carrying out the invention may also reflect light to some degree although the main property of the preferred materials is that of scattering to provide a uniform intensity light output.

[0065] 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 conduits).

[0066] FIG. 14 shows the addition of a reflective video projection device 28 such as the Texas Instruments Digital Light Processing processor or thin film transistor screen or liquid crystal display, and image projection optics 25 enabling static or moving image projection. A light ray 26 from the exit port shows a typical path to the projection optics 25.

[0067] FIG. 15 shows the addition of a transmissive video projection device 27 such as a thin film transistor screen or liquid crystal display and image projection optics 25 enabling static or moving image projection. A light ray 26 from the exit port shows a typical path to the projection optics 25.

[0068] Other features, benefits and advantages of the invention will be apparent to those of ordinary skill in the art and the invention is deemed to include all variants within the scope of the claims.