Abstract:
A plurality of light sources, each radiating a color of light; a corresponding plurality of reflectors are arranged and configured so that the reflector reflects light from a predetermined one of the plurality of light sources. The reflected light from the plurality of reflectors is mixed to generate a composite light from the plurality of light sources. A sequenced or stacked array of the light sources and dichroic reflectors mixes the reflected light from the reflectors. Each reflector is positioned on a common optical axis with an aligned corresponding one of the plurality of light sources to provide a light source and reflector pair. Each reflector is coated with a dichroic filter material which reflects the color of light radiated by the corresponding light source of the pair, and which transmits light radiated by all preceding light sources in the sequenced array.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is related to U.S. Provisional Patent Application Ser. No. 60/491,694 filed on Aug. 1, 2003, which is incorporated herein by reference and to which priority is claimed pursuant to 35 USC 119. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to the field of apparatus and method for using light emitting diodes (LED) or other light sources of differing wavelengths in an approximately unitized beam, sharing similar angle space.  
         [0004]     2. Description of the Prior Art  
         [0005]     Color projection systems have been used for many years to project motion pictures and still photographs onto screens for viewing. More recently, presentations using multimedia projection systems have become popular for conducting sales demonstrations, business meetings, and classroom instruction. In a common operating mode, multimedia projection systems receive analog video signals from a personal computer (“PC”). The video signals may represent still, partial-, or full-motion display images of a type rendered by the PC. The analog video signals are typically converted in the projection system into digital video signals, and the signals are electronically conditioned and processed to control an image-forming device, such as a liquid crystal display (“LCD”) or a digital micromirror device (“DMD”).  
         [0006]     A popular type of multimedia projection system employs a broad spectrum light source and optical path components upstream and downstream of the image-forming device to project the image onto a display screen.  
         [0007]     However, the optical performance of conventional projectors is often less than satisfactory. For example, suitable projected image brightness is difficult to achieve, especially when using compact portable color projectors in a well-lighted room. The projectors typically use high intensity arc lamps as their light source and then filter out all of the light except for blue, green, and red light and employ three separate light paths or some forms of sequential color modulator to coordinate color image data. Such white light systems typically use a series of dichroic mirrors to fraction the light into red, green and blue wavelengths and then remix the light from each beam after passing each through an LCD mask which as been configured to provide a red, green and blue component of the final desired image. The optical path lengths are long and there are a number of reflections and filtration steps which must be performed with resulting loss in intensity and resolution. The physical package which must be provided for such a system can be large.  
         [0008]     Because LCD displays have significant light attenuation and triple path color light paths are heavy and bulky, portable multimedia projectors typically employ DMD displays in a single light path configuration. Producing a projected color image with this configuration typically requires projecting a frame sequential image through a sequential color modulator, such as a color wheel.  
         [0009]     Another form of color illuminator combines red, green, blue, cyan and amber colored LED sources in order to increase brightness in a complex reflected optical path to mix the resultant light in an integrator rod. Again the optical path ways are long, the optical system is necessarily physically large and the overall performance is still subject to intensity and collimation losses. In this case the output of the integrator rod is a single color and a plurality of such color illuminators must be employed to obtain a large scale pixel image.  
         [0010]     What is needed is a some kind of a controllable color light source which is not subject to the inherent disadvantages of such prior art displays or other conventional colored light systems.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     The invention pertains to the use of light emitting diodes (LED) in a device that combines the energy from multiple LEDs of differing wavelengths into an approximate unitized beam, sharing similar angle space or projection beam envelope. The invention provides for the efficient collection of energy radiating from two or more LEDs, and then distributes this energy into a common physical space or solid angle of radiation. The invention further includes thermally managing the device and contemplates electronic control of the individual LEDs.  
         [0012]     By choosing different color outputs for the LED and since the LED are individually controllable, device may be used generally in a wide variety of applications as a generic source of selectively controllable colored light.  
         [0013]     The invention is a highly efficient LED based device with an energy source, at least two LEDs, at least two reflectors, a means for mounting each of the LEDs over the reflectors which double as heat sinks such as a thermally conductive bridge, and a housing. The LEDs are mounted on a heat conductive material or bridge that provides the thermal management for the LEDs. This bridge also situates the LEDs over the reflectors with the primary light direction of the LEDs facing rearwardly into the reflectors. The reflectors then reflect the light back out the front facing direction of the device. The mechanical design of the bridge is a predetermined compromise between occluding the light returning from the reflectors and providing the thermal management for the LEDs.  
         [0014]     The reflectors may be designed to provide a collimated beam, a convergent beam or a divergent beam. The reflectors may have a common conic shape or not and may be faceted or dimpled or otherwise modified to provide a desired beam pattern. Any configuration or form of optical reflector now known or later devised can be equivalently employed. The device may optionally have at least one lens or surface(s) that further control(s) the light from the reflectors.  
         [0015]     More particularly the invention is an apparatus for generating a selected color of light comprising a plurality of light sources disposed in a housing, each radiating a color of light and a corresponding plurality of reflectors disposed in the housing. Each reflector is longitudinally paired with a light source to reflect light from a paired one of the plurality of light sources. The light sources and reflectors are arranged and configured to mix reflected light from the reflectors into a composite light beam from the plurality of light sources. The arrangement in the illustrated embodiment is comprised a sequenced or stacked array of the light sources and dichroic reflectors. In other words, the arrangement of light sources and reflectors comprises a sequenced array of the plurality of light sources and reflectors in an alternating pairs of reflectors and light sources. Each reflector is positioned on a common optical axis with an aligned corresponding one of the plurality of light sources to provide a light source and reflector pair. Each reflector with the possible exception of the first reflector of the sequenced array is coated with a dichroic filter material which reflects the color of light radiated by the corresponding light source of the pair, and which transmits light radiated by all preceding light sources in the sequenced array. The result is that the stacked assembly of light sources and reflectors have an overall envelope radius or size which is approximately equal to or comparable to the beam aperture radius or size. The stacked assembly is compact and the optical path length of the light components and the number of reflections encountered is minimized. Using this design arrays of such stacked assemblies can be assembled which are arbitrarily color controllable, have very little dead space, have very little source intensity loss, and produce highly collimated beams.  
         [0016]     The plurality of light sources generate a full color spectrum of visible light, or more specifically green, blue and red light in selected amounts. The apparatus further comprising means for individually controlling the intensity of light from each of the light sources, such as conventional drive circuits coupled to the light sources.  
         [0017]     The apparatus further comprising a corresponding plurality of heat sinks. Each heat sink is thermally coupled to one of the plurality of light sources. The heat sink further comprises a fixture for mounting each corresponding light source relative to the corresponding reflector. The apparatus still further comprises a housing thermally coupled to each of the heat sinks.  
         [0018]     The plurality of light sources and reflectors are assembled into a unit and a plurality of such units is arranged and configured into a compound system or array. The compound system includes, but is not limited to, such applications as a large format LED display screen, a backlight for an LCD screen, a light source for a digital light projection system, a digital cinema projector, a color video projector, a color changing light source for a display, an architectural light, a theater and stage light, or a light source for a color corrected display system.  
         [0019]     Each unit mixes the light by time-multiplexing the generation of colored light from the unit by cycling individual light sources to generate corresponding color images.  
         [0020]     In addition the individual units may be controlled to radiate at the same time with different intensities to form what can be defined as color multiplexed light.  
         [0021]     The invention also includes a method of providing and operating the apparatus described above.  
         [0022]     While the apparatus and method has or will be described for the sake of grammatical fluidity with functional explanations, it is to be expressly understood that the claims, unless expressly formulated under 35 USC 112, are not to be construed as necessarily limited in any way by the construction of “means” or “steps” limitations, but are to be accorded the full scope of the meaning and equivalents of the definition provided by the claims under the judicial doctrine of equivalents, and in the case where the claims are expressly formulated under 35 USC 112 are to be accorded full statutory equivalents under 35 USC 112. The invention can be better visualized by turning now to the following drawings wherein like elements are referenced by like numerals. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a perspective view of one embodiment of the invention in which three LEDs are used and shown in phantom outline in a housing.  
         [0024]      FIG. 2  is a side cross-sectional view of the embodiment of  FIG. 1  as seen through section lines  2 - 2  of  FIG. 3 .  
         [0025]      FIG. 3  is an end plan view of the embodiment of  FIG. 2 .  
     
    
       [0026]     The invention and its various embodiments can now be better understood by turning to the following detailed description of the preferred embodiments which are presented as illustrated examples of the invention defined in the claims. It is expressly understood that the invention as defined by the claims may be broader than the illustrated embodiments described below.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Turn to  FIGS. 1-3  wherein the illustrated embodiment of the invention is depicted.  FIG. 1  is a perspective view of the device, generally denoted by reference numeral  20 , which is comprised of a housing  1  and various optical elements described below. Housing  1  in the illustrated embodiment serves to align the various optical elements of the device. One of the optical elements is a reflector  2  which is disposed in a rearward position of device  20  as shown in the left end portion of the side cross-sectional view of  FIG. 2  and which can be coated to reflect substantially all the light from light emitting diode, LED,  3 , which is held in position over reflector  2  by means of a heat sink  4 . By LED it is understood to include a solid state light emitting diode package, which includes a semiconductor substrate in which the light emitting junction is defined, electrical leads, passivation layers and a lens or lens assembly mounted on or forming part of the passivating package around the junction and substrate. The illustrated embodiment employs an LED  3 , but it is to be understood that any light source may be employed which is now known or later devised, such as incandescent, fluorescent, arc, or gas plasma sources as a few examples. Thus, wherever LED is referred, it is to be understood according to the context that any light source could be equivalently substituted.  
         [0028]     The light reflected by reflector  2 , represented by a light ray  12  passes through the reflector  6 , where it combines with the light ray  13  radiating from LED  5  suspended by means of heat sink  7  and reflecting off reflector  6 . Reflector  6  is coated with a material which is commonly referred to as a thin film or a dichroic filter. A dichroic filter material selectively transmits light according to its wavelength and are well known to the art. This filter material on reflector  6  is designed or selected to reflect the wavelength of LED  5 , while transmitting the wavelength of LED  3 .  
         [0029]     Rays  12  and  13  pass through reflector  9  and combine with the ray  14  that radiates from LED  8 , which is suspended on heat sink  10  reflecting off reflector  9 . Reflector  9 , similarly as reflector  6 , is coated with a dichroic filter material designed to reflect the wavelength of LED  8  and transmit all other wavelengths. It is also within the scope of the invention to select the dichroic filter materials on reflectors  2 ,  6  and  9  to reflect or transmit more specific wavelengths other than those radiated by the LEDs  3 ,  5  and  8  of the device  20 . It must also be understood that less or more than three LEDs may be combined in device  20  according to the foregoing teachings.  
         [0030]     Heat sinks  4 ,  7  and  10  are typically comprised of metal but any thermally conductive material may be employed. Heat sinks  4 ,  7  and  10  are formed in the shape of a cylindrical radially defined body which flushly mounts into housing  1  with a pair a diametrically extending arms leading to a central mounting boss to which the corresponding LED is mounted. Hence, housing  1  may also be thermally conductive and be employed in the heat management of LEDs  3 ,  5  and  8 . The arms may carry wires and/or form part of the electrical circuit with their respective LEDs.  FIG. 3  is an end plan view as seen from the right end of the side cross-sectional depiction of  FIG. 2 . In the illustrated embodiment the arms of heat sinks  4 ,  7  and  10  are azimuthally offset from each other so that the arms of all three heat sinks  4 ,  7  and  10  are not angularly aligned with each other. This assists in reducing the light shadow or obstruction caused by the arms.  
         [0031]     Alternative means of mounting and thermally handling the LEDs or light sources is also included within the scope of the invention. For example, the heat source could be devised as a thermally conductive, flat transparent substrate, such as made from glass, quartz, heat resistant plastic, or a crystalline material to which the LED or light source is mounted and thermally coupled, while transparent indium tin oxide leads are disposed on the substrate to provide electrical connection to the LED or light source.  
         [0032]     The lens or lenses  11  may be optionally provided to spread or converge the combined light beam, asymmetrically or not, or provide diffusion or other optical effects according to conventional design options.  
         [0033]     By selecting appropriate colored LEDs  2 ,  5 ,  8  and controlling the output of the individual LEDs  2 ,  5 ,  8 , the device  20  could be used either alone or in arrays for several different and distinct purposes. These uses include: a pixel for large format LED display screens, a backlight for LCD screens, a light source for projection systems, a color changing light source for displays, architectural lighting, theater and stage lighting, a light source for color corrected display systems and many other lighting related applications.  
         [0034]     In a preferred embodiment as shown in  FIGS. 1-3 , the device  20  is shown with three LEDs  3 ,  5 ,  8 . One of LEDs  3 ,  5 ,  8  is red, one is green and one is blue. The red LED  3 , for example, would preferably be farthest from the front of the device  20  and situated over a highly reflective concave surface of reflector  2 . The light emitted from the red LED  3  reflects off the surface of reflector  2  and passes through a plane that is defined as the “mouth” of the reflector  2 . The green LED  5  is situated over a reflector  6  that is coated in such a way as to allow the red light to pass through it and to reflect the green light radiated from the green LED  5  situated over reflector  6  in a similar manner to the red LED  3 . The red and green light can now be considered mixed in the same physical space or at the mouth of reflector  6 . The next LED  8  is blue and is similarly situated over a reflector  9  that is coated to reflect the blue light radiated from the blue LED  8  and to allow the red and green light to pass through it. The light from all three LEDs  3 ,  5 , and  8  can then be considered as mixed in the same physical space or at the mouth of reflector  9 . By separately adjusting the light output of the individual LEDs  3 ,  5 , and  8  by means of any conventional LED drive circuit (not shown) in theory any color of light beam can be produced by the invention.  
         [0035]     The optical output of device  20  can be modified by use of a lens or a lens assembly  11  in front of the output mixed beam transmitted from the mouth of reflector  9 . Lenses  11  could provide beam spreading or converging. Alternatively, a semi-transparent material could be placed in front of the beam to create a rear-illuminated display. A plurality of devices  20  can be arrayed to create additional compound devices such as a large format video screens.  
         [0036]     The device can be used for illumination for projection systems alone or in an array. Due to the devices very collimated beam, the device could be used as a light source for liquid crystal display (LCD) based, digital light projection (DLP) based or other similarly controlled projection systems, including digital cinema. By controlling the individual LED current the white point, as defined as the neutral or all-colors spectral mix, can be modified as desired for systems made from a plurality of devices  20 .  
         [0037]     An additional capability for LCD or DLP systems comprised of a plurality of devices  20  is a time-multiplexed color generation by cycling the individual LEDs to alternate color frames in a video. For example, if it is desired to have a 30 frames per second display, then the red LED  3  can be turned on with the green LED  5  and blue LED  8  off for about {fraction (1/90)}th of a second while the display shows the first frame&#39;s red content. Then the green LED  5  would turn on and the red LED  3  and the blue LED  8  off for about the next {fraction (1/90)}th second. Then the blue LED  8  is turn on and the red LED  3  and green LED  5  off for about {fraction (1/90)} th  of a second. The cycle then repeats for the next frame. In contrast, the sequential color projection of the prior art uses a rotating color filter wheel in a white beam.  
         [0038]     Hence, it can now be appreciated that the invention provides an electronically controllable colored light source which is physically compact and provides a single, selectively controllable, colored beam of light with a minimum of the number of optical elements and reflective surfaces and a minimum optical path length. The invention is advantageously characterized as having an overall package envelope which is substantially the same as or close in size to ultimate useful light aperture of the beam.  
         [0039]     The nature of the invention is such than when no light is being produced, the dark field seen looking into the stacked area is very high since the reflective surfaces are well shielded from stray or ambient light. Hence, when a plurality of illuminators are used in an array, one illuminator for each pixel, the contrast between lit and unlit pixels of the image produced by the array is high. This is of particular advantage in large area displays with high information content (LADHIC) such as are used in many sports venues.  
         [0040]     Further, the fact that the beam aperture is very nearly the same size as the envelope size for the stack, allows the stacks to be combined in very compact arrays with very little dead space, which is of particular advantage for use in colored spot lights used for theatrical illumination. The design of the stacks allows them to be made with any space-filling cross-sectional shape, such as square, hexagonal, octagonal and the like. Further, the design also lends itself to inexpensive fabrication since the components can be miniaturized and mass-produced in plastics or other inexpensive and easily manufacturable materials, again which is advantageous in applications where arrays of the stacked assemblies are used.  
         [0041]     Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiment has been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following claims. For example, notwithstanding the fact that the elements of a claim are set forth below in a certain combination, it must be expressly understood that the invention includes other combinations of fewer, more or different elements, which are disclosed in above even when not initially claimed in such combinations.  
         [0042]     The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification structure, material or acts beyond the scope of the commonly defined meanings. Thus if an element can be understood in the context of this specification as including more than one meaning, then its use in a claim must be understood as being generic to all possible meanings supported by the specification and by the word itself.  
         [0043]     The definitions of the words or elements of the following claims are, therefore, defined in this specification to include not only the combination of elements which are literally set forth, but all equivalent structure, material or acts for performing substantially the same function in substantially the same way to obtain substantially the same result. In this sense it is therefore contemplated that an equivalent substitution of two or more elements may be made for any one of the elements in the claims below or that a single element may be substituted for two or more elements in a claim. Although elements may be described above as acting in certain combinations and even initially claimed as such, it is to be expressly understood that one or more elements from a claimed combination can in some cases be excised from the combination and that the claimed combination may be directed to a subcombination or variation of a subcombination.  
         [0044]     Insubstantial changes from the claimed subject matter as viewed by a person with ordinary skill in the art, now known or later devised, are expressly contemplated as being equivalently within the scope of the claims. Therefore, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements.  
         [0045]     The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptionally equivalent, what can be obviously substituted and also what essentially incorporates the essential idea of the invention.