Abstract:
A light collection system includes at least one light source, a light tunnel having reflective walls and a collimating plate at the light output end of the tunnel. The collimating plate includes an optical element array. The element array receives the light emitted from the light source and outputs part of the light at a desired cone angle and reflects the remainder back into the tunnel toward the light source. The light is “recycled” in the tunnel until the light either exits the collection system through the collimating plate or gets absorbed within the collection system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of: 
    (1) U.S. patent application Ser. No. 10/458,390 filed on Jun. 10, 2003, titled “Light Guide Array, Fabrication Methods, and Optical System Employing Same”;     (2) U.S. patent application Ser. No. 11/066,605, titled “Compact Polarization Conversion System for Optical Displays,” filed on Feb. 25, 2005;     (3) U.S. patent application Ser. No. 11/066,616, titled “Compact Projection System Including a Light Guide Array,” filed on Feb. 25, 2005;     (4) U.S. patent application Ser. No. 11/067,591, titled “Light Recycler and Color Display System Including Same,” filed on Feb. 25, 2005; and     (5) U.S. patent application No. 11/317,189, titled “Light Recovery System and Display Systems Employing Same”, filed on Dec. 22, 2005.    
 
         [0007]     This application also claims the benefit of U.S. Provisional Application No. 60/719,155 filed on Sep. 21, 2005.  
         [0008]     This application is also related to the following patent applications: 
    (1) U.S. Patent Application No.  60 / 719 , 109 , titled “Method and System for LED Light Extraction Using Optical Elements”, filed on Sep. 21, 2005; and     (2) U.S. patent application Ser. No. 11/232,310, titled “Method and Apparatus for Reducing Laser Speckle”, filed on Sep. 21, 2005.    
 
         [0011]     The subject matter of all of the aforementioned applications is hereby incorporated by reference as though set forth herein in full. 
     
    
     TECHNICAL FIELD  
       [0012]     The invention relates generally to systems for collecting and condensing electromagnetic radiation, such as light. More particularly, the disclosure relates to a system for providing a high radiance to a small target such as a display panel in a projection system.  
       BACKGROUND  
       [0013]     Electromagnetic radiation such as light can be collected and condensed using imaging or non-imaging systems. An imaging system produces an image of an arc at a certain location in an optical path. A non-imaging system does not produce an image of an arc, but delivers an optical beam with a certain area, aspect ratio and cone angle.  
         [0014]     A common method for light collection is based on a system using a parabolic or ellipsoid reflector of the imaging or non-imaging type.  FIG. 1A  shows a prior art lamp/reflector system in which a lamp  12  is placed at a first focus of an ellipsoid reflector  11 . The ellipsoid reflector  11  focuses the light beam  13  into a second focus  14  located on the optical axis  5 . A target (not shown) is usually placed at this second focus  14 .  
         [0015]      FIG. 1B  shows another prior art lamp/reflector system in which a lamp  22  is placed at a focus of a parabolic reflector  21 . The parabolic reflector  21  delivers a collimated light beam  23  parallel to an optical axis  15 . A focusing lens (not shown) can be used to collect the collimated beam  23  and focus it into a target (not shown) located somewhere on the optical axis  15 .  
         [0016]     Both systems shown in  FIGS. 1A-1B  are on-axis systems, since the components are aligned along an optical axis. Systems based on off-axis configurations are also known. For example, U.S. Pat. Nos. 5,414,600 and 5,430,634 describe off-axis collection systems of the imaging type. Non-imaging collection systems are discussed, for example, in U.S. Pat. No. 5,271,077 to Brockman, Kacia et al. and U.S. Pat. No. 6,554,456 to Buelow et al.  
         [0017]     Non-imaging light collection systems have been described in U.S. Pat. No. 5,773,918 to Dolan et al. and U.S. Pat. No. 6,509,675 to MacLennan et al. In such systems, a reflective coating is applied directly to the bulb surface of an electrodeless lamp (and sometimes a reflective jacket surrounds the bulb) leaving a port open in the reflective coating (or the reflective jacket) to form an aperture. Light exits the collection system through the aperture and can be collimated via known imaging or non-imaging optics to obtain the desired cone angle. These collection systems do not provide a way to control the spatial distribution of light in terms of angle and intensity at each point across the aperture. In addition, the Dolan and MacLennan patents focus on electrodeless lamps and do not provide effective means to apply such collection schemes to electroded lamps.  
         [0018]     Many known electromagnetic radiation collection systems suffer from the following problems. First, many of these systems are relatively large, making them less attractive for many applications such as portable projection display systems. Second, these systems provide limited control over the spatial distribution of delivered light in terms of intensity and angle. Third, due to the large optical aberrations typical of these reflector types, etendue (angular extent) of the light beam is not preserved in most cases, leading to radiation losses at the target. Finally, many of these systems collect only part of the light emitted from a source. Specifically, they collect those light rays that strike the reflector after being emitted from the source. Light rays that do not strike the reflector typically do not get collected, and are thus wasted.  
         [0019]     Therefore, there is a need for compact, lightweight, and efficient light collection system that provides control over spatial distribution of light in terms of intensity and angle over a certain target area, such as the active area of a display panel.  
       SUMMARY  
       [0020]     It is an advantage of the present invention to provide a compact, light weight, and efficient light collection system capable of producing a light beam having a desired cross-section and spatial distribution of light, in terms of intensity and angle. Such a light collection system can efficiently couple light from sources having different sizes and shapes into targets of various shapes and sizes. For example, using the collection systems disclosed herein, arc lamps having arc sizes of more than 1 mm long can be efficiently coupled to small illumination targets, thus, enabling the use of long arc lamps that are less expensive and have longer lives in projection systems.  
         [0021]     In accordance with an exemplary embodiment of the invention, optical element arrays and light guides are used to form a collection system this is capable of providing a desired spatial distribution of light in terms of angle and intensity over a certain target area, such as that of a display panel. The collection system includes at least one light source, a light tunnel having reflective walls and a collimating plate at the light output end of the tunnel. The collimating plate includes an optical element array. The micro-element array receives the light emitted from the light source and outputs part of the light at a desired cone angle and reflects the remainder back into the tunnel toward the light source. The light is “recycled” in the tunnel until the light either exits the collection system through the collimating plate or gets absorbed within the collection system.  
         [0022]     In addition to the embodiments described herein, other embodiments, features, aspects, advantages, systems and methods of the invention will be or will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional embodiments, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     It is to be understood that the drawings are solely for purposes of illustration and not as a definition of the limits of the invention. Furthermore, it is to be understood that the drawings are not necessarily drawn to scale and that, unless otherwise stated, they are merely intended to conceptually illustrate the structures and methods described herein.  
         [0024]      FIG. 1A  is a cross-sectional view of a prior art collection system, which utilizes an ellipsoid reflector for light collection.  
         [0025]      FIG. 1B  is a cross-sectional view of a second prior art collection system, which utilizes a parabolic reflector for light collection.  
         [0026]      FIG. 2A  shows a perspective view of a collection system utilizing a light tunnel and a collimating plate for light collection.  
         [0027]      FIG. 2B  shows a perspective view of the light tunnel shown in  FIG. 2A .  
         [0028]      FIG. 2C  shows a perspective view of the collimating plate shown in  FIG. 2A .  
         [0029]      FIG. 2D  shows a perspective view of the light source shown in  FIG. 2A .  
         [0030]      FIG. 2E  shows a cross-sectional view of the collection system of  FIG. 2A .  
         [0031]      FIG. 2F  shows a cross-sectional view of the collimating plate shown in  FIGS. 2A and 2C .  
         [0032]      FIG. 2G  shows a perspective view of the aperture array shown in  FIGS. 2C and 2F .  
         [0033]      FIG. 2H  shows a perspective view of the micro-waveguide and micro-lens arrays shown in  FIGS. 2C and 2F .  
         [0034]      FIG. 3A  shows a perspective view of a collimating plate consisting of an aperture array and a micro-waveguide array (with no micro-lens array).  
         [0035]      FIG. 3B  shows a cross-sectional view of the collimating plate of  FIG. 3A .  
         [0036]      FIG. 3A  shows cross-sectional view of another configuration of the collection system where the light source electrodes are placed within the xy-plane.  
         [0037]      FIG. 3B  shows cross-sectional view of an alternative configuration of the collection system where the light source is attached to the back of the light tunnel.  
         [0038]      FIG. 3C  shows a top view of a collimating plate utilizing hollow micro-tunnel and aperture arrays for light collimation.  
         [0039]      FIG. 3D  shows a cross-sectional view (in the yz-plane) of the collimating plate of  FIG. 3C .  
         [0040]      FIG. 3E  shows a perspective view of a collimating plate consisting of an aperture array and a micro-lens array (with no micro-waveguide array).  
         [0041]      FIG. 3F  shows an exploded view of the collimating plate of  FIG. 3E .  
         [0042]      FIG. 3G  shows a cross-sectional view (in the yz-plane) of the collimating plate of  FIG. 3E .  
         [0043]      FIG. 4A  shows a cross-sectional view (in the xy-plane) of a collection system utilizing a collimating plate, a light tunnel and a light source.  
         [0044]      FIG. 4B  shows a cross-sectional view (in the xy-plane) of a collection system utilizing a collimating plate, a light tunnel and a light source attached to the back side of the tunnel.  
         [0045]      FIG. 4C  shows a cross-sectional view (in the xy-plane) of a collection system utilizing a collimating plate, a light tunnel, a solid light pipe and a light source.  
         [0046]      FIG. 4D  shows a cross-sectional view (in the xy-plane) of a collection system utilizing a collimating plate, a light tunnel, a solid light pipe and a light source attached to the back side of the tunnel.  
         [0047]      FIG. 4E  shows a perspective view of a collection system utilizing two light sources and a light tunnel.  
         [0048]      FIG. 5A  shows a perspective view of a collection system utilizing a light source having a back reflector.  
         [0049]      FIG. 5B  shows a cross-sectional view (in the yz-plane) of the collection system of  FIG. 5A .  
         [0050]      FIG. 5C  shows a cross-sectional view (in the xy-plane) of the collection system of  FIG. 5A .  
         [0051]      FIG. 5D  shows a cross-sectional view (in the yz-plane) of the source of  FIG. 5A .  
         [0052]      FIG. 5E  shows a cross-sectional view (in the xz-plane) at the back side of the tunnel of the collection system of  FIG. 5A .  
         [0053]      FIG. 6A-6C  shows a cross-sectional view of the process of partly coating a source and its electrodes with a reflective coating.  
         [0054]      FIG. 6D  shows a cross-sectional view of the source of  FIG. 6C  attached within a light tunnel.  
         [0055]      FIG. 6E  shows a cross-sectional view of another variation of the source of  FIG.6C  attached within a light tunnel.  
         [0056]      FIG. 6F  shows a cross-sectional view of a source with a cylindrical bulb attached within a light tunnel.  
         [0057]      FIG. 7  shows a cross-sectional view (in the yz-plane) of a collection system providing light to a solid pipe or hollow tunnel.  
         [0058]      FIG. 8  is a cross-sectional view of a collection system suitable for an electrodeless lamp excited by microwave energy.  
         [0059]      FIG. 9  is a cross-sectional view of a collection system suitable for an electrodeless lamp excited by high energy electromagnetic radiation.  
     
    
     DETAILED DESCRIPTION  
       [0060]     The following detailed description, which references to and incorporates the drawings, describes and illustrates one or more specific embodiments of the invention. These embodiments, offered not to limit but only to exemplify and teach the invention, are shown and described in sufficient detail to enable those skilled in the art to practice the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art.  
         [0061]      FIG. 2A  shows a perspective view of a collection system  30  utilizing one light source  32 , a tunnel  33  and a collimating plate  34 . As shown in  FIG. 2D , the bulb  32   a  of the radiation source  32  is placed within the tunnel  33  so that most of emitted light is guided within the light tunnel  33 . The support rod (or electrodes)  32   b  of the bulb  32   a  extend through two of the tunnel sidewalls  33   b  (see  FIG. 2B ). The radiation source  32  can be a filament lamp or an arc lamp such as a xenon lamp, a metal halide lamp, an HID lamp or a mercury lamp. Electrodeless and electroded lamps can be used as light sources.  
         [0062]     As shown in  FIG. 2B , the hollow tunnel  33  consists of four sidewalls  33   b  and a back side  33   a , which are coated with a highly reflective coating. The coating can be specular, diffuse reflector or combinations of both (i.e., part of the sidewalls has diffuse and other parts have specular reflector). The exit face  33   c  of the tunnel  33  is open. The collimating plate  34  is attached to the exit face  33   c  of the tunnel  33  as shown in  FIG. 2A . The collimating plate  34  receives light exiting the tunnel  33  at its light input surface  37  and outputs collimated light from its light output surface  39 .  
         [0063]     Although the tunnel  33  is shown as being rectangular shaped, it can have other shapes, such as being cylindrical.  
         [0064]      FIG. 2C  shows a perspective view of the collimating plate  34 , which consists of an aperture plate  34   a , micro-waveguide array  34   b  and a micro-lens array  34   c . Each micro-lens corresponds to a micro-waveguide and a micro-aperture. As shown in  FIG. 2G , the aperture array  34   a  comprises a plate made of a highly-transmissive material  34   a   1  to electromagnetic radiation with a patterned reflective coating  34   a   2  applied to its top surface. A perspective view of the micro-waveguide array  34   b  and micro-lens array  34   c  is shown in  FIG. 2H . Both arrays  34   b  and  34   c  are made on a single glass plate. A cross-sectional view of the aperture array  34   a , micro-waveguide array  34   b  and micro-lens array  34   c  is shown in  FIG. 2F .  
         [0065]     Design parameters of each optical element (e.g., micro-waveguide, micro-lens, aperture or micro-tunnel) within an array  34   a ,  34   b  and  34   c  include shape and size of entrance and exit apertures, depth, sidewalls shape and taper, and orientation. The elements within an array  34   a ,  34   b  and  34   c  can have uniform, non-uniform, random or non-random distributions and range from one element to millions with each element being distinct in its design parameters. The size of the entrance/exit aperture of each element is preferably greater than or equal to 5 μm in case of visible light in order to avoid light diffraction phenomenon, in a range of about 5 μm-50 μm. However, it is possible to design elements with sizes of entrance/exit aperture being less than 5 μm. In such case, the design should consider the diffraction phenomenon and behavior of light at such scales to provide homogeneous light distributions in terms of intensity, viewing angle and color over a certain area. Such elements can be arranged as a one-dimensional array, two-dimensional array, circular array and can be aligned or oriented individually.  
         [0066]     In addition, the collimating plate  34  can have a smaller size than the exit face  33   c  of the tunnel  33  (see  FIG. 2B ) and its shape can be rectangular, square, circular or any other arbitrary shape.  
         [0067]     The operation of the light collection system  30  is described as follows. Part of the electromagnetic radiation emitted by the source  32  travels directly toward the collimating plate  34  and the some travels toward the back side of the tunnel where it gets reflected toward the collimating plate  34 . This radiation is guided within the light tunnel  33  until it impinges on the collimating plate  34 , which passes part of this electromagnetic radiation through the entrance apertures  34   b   1  (see the exploded view of  FIG. 2F ) of the micro-waveguide array  34   b . The remainder of the radiation gets reflected off of the reflective coating  34   a   2  (see  FIG. 2F ) of the aperture array  34   a  and travels toward the source  32 . Most of this reflected light impinges on the back side of the tunnel  33  and gets reflected back toward the collimating plate  34 . This process continues until most of the radiation passes through the collimating plate  34 .  
         [0068]     Radiation received by the collimating plate  34  experiences total internal reflection within the micro-waveguides of array  34   b  and becomes highly collimated as it exits array  34   b . This collimated radiation enters and exits the micro-lens array  34   c  via refraction and become even more collimated. In addition to this high level of collimation, collection system  30  provides control over the spatial distribution of output radiation in terms of intensity and cone angle at the location of each element. The spatial distribution of output radiation can be varied by changing the arrangement, uniformity, designs, number and density of the optical elements included in the collimating plate  34 .  
         [0069]     Since the collection system  30  is a closed one, the reflected light beam gets reflected off of the reflective coating at the back side of the tunnel and travels back toward the micro-waveguide array. The light is recycled in the tunnel until the light either exits the collection system through the collimating plate or gets absorbed within the collection system.  
         [0070]      FIGS. 3A-3G  show collimating plates  44 ,  54 ,  64  with alternative designs and structures. These alternative collimating plates  44 ,  54 ,  64  can be substituted for the collimating plate  34  shown in the collection systems  30 ,  130 ,  330 ,  530 ,  630  disclosed herein.  
         [0071]      FIG. 3A and 3B  show perspective and cross-sectional views of a collimating plate  44  consisting of a micro-waveguide array  34   b  and an aperture array  34   a .  FIG. 3C and 3D  show top and cross-sectional views of a collimating plate  54  consisting of an aperture array  44   a integrated with a hollow micro-tunnel array  44   b  on a single plate. The internal sidewalls  45   b  (exploded view of  FIG. 3C ) of each micro-tunnel are coated with a highly reflective coating  46   b  ( FIG. 3D ) of the specular type. The aperture array  44   a  consists of a reflective coating  46   a  (can be specular or diffuse type) applied to the areas surrounding the entrance aperture  45   a  of each micro-tunnel. In this type of collimating plate  54 , the radiation enters through the entrance aperture  45   a  of each micro-tunnel, gets reflected off of the reflective coating  46   b  applied to the micro-tunnel&#39;s sidewalls  45   b  and exits the exit aperture  45   c  of each micro-tunnel as a more collimated radiation. The remainder of received radiation gets reflected by the reflective aperture array  44   a . The advantages of collimating plate  54  are compactness and high transmission efficiency of radiation without the need for antireflective (AR) coatings at the entrance  45   a  and exit  45   c  apertures of its micro-tunnels.  
         [0072]     The collimating plate  54  shown in FIGS.  3 C-D is discribed in U.S. patent application Ser. No. 10/458,390 filed on Jun. 10, 2003, titled “Light Guide Array, Fabrication Methods, and Optical System Employing Same”, which is incorporated by reference.  
         [0073]      FIGS. 3E, 3F  and  3 G show perspective, exploded and cross-sectional views of a collimating plate  64  consisting of an aperture array  64   a  and a micro-lens array  64   b  made on a single plate. In this case, the micro-lens array  64   b  performs the collimation function of delivered radiation via refraction.  
         [0074]     U.S. Pat. Nos. 5,598,281 and 5,396,350, which are hereby incorporated by reference, discuss various designs of additional collimating plates which can be used in the collection systems disclosed herein. However, micro-waveguide arrays of these two patents required the application of a specular reflective coating on the sidewalls of individual solid micro-waveguides. Such a requirement is necessary for their intended backlight applications where the cone angle of received light is too large to be collimated via total internal reflection.  
         [0075]     Two additional implementations of collection systems  130 ,  230  are shown in FIGS.  4 A-B, respectively.  
         [0076]      FIG. 4A  shows a cross-sectional view of the collection system  130  with the source  32  being oriented in the xy-plane rather than the yz-plane as shown in  FIGS. 2A and 2E .  FIG. 4B  shows a cross-sectional view of the collection system  230  with the source  32  being oriented in the yz-plane and attached to the back side of the tunnel  33 . Other orientations are possible but in general, it is preferable to align the cone angle of the majority of the radiation along the optical axis (i.e., the y-axis) in order to have better collimation and higher transmission efficiency.  
         [0077]     FIGS.  4 C-D show, respectively, two other implementations of collection system  330  and  430  utilizing solid pipes  333   b  and  433   b  as well as hollow tunnels  333   a  and  433   a . In such cases, the source  32  is placed (completely or partly) within the hollow tunnels  333   a  and  433   a . Such arrangements make it easier to manufacture the source and tunnel as a separate unit, thus, allowing assembly of the collection systems using hollow tunnels or solid pipes with various lengths and sizes.  
         [0078]      FIG. 4E  shows a collection system  530  consisting of a collimating plate  34 , tunnel  33  and two sources  32   a  and  32   b  connected serially within the tunnel  33 . More than two sources can be placed serially or in parallel within the light tunnel  33 . The serial connection is preferable since it does not require increasing the size of the cross section of the tunnel  33  to accommodate two or more sources connected in parallel. Increasing the cross section of the tunnel  33  increases the optical extent of delivered radiation and reduces the amount of radiation coupled to a target.  
         [0079]     FIGS.  5 A-E show another collection system  630 . The collection system  630  consists of a collimating plate  34 , tunnel  33  and source  632 , which is partly placed within the tunnel  33 .  FIGS. 5B and 5C  show cross-sectional views of the system  630  in the yz- and xy-planes, respectively.  FIG. 5D and 5E  show cross-sectional views of the source  632  in the yz- and xz-planes, respectively. A reflective coating  632   a  is applied to the electrode sealing and to one-half the outside surface of the bulb. In this case, the reflective coating on the bulb&#39;s surface focuses part of the radiation through the arc and toward the collimating plate  34 . Radiation traveling toward the backside of the tunnel  33  is reflected back toward the collimating plate  34  either by the reflective coating  632   a  or by the reflective coating  633  on the back side of the tunnel  33  as shown in  FIG. 5E .  
         [0080]      FIGS. 6A-6D  show the steps of applying a reflective coating (specular or diffuse) directly to the electrodes of an electroded arc lamp and the cross sections of the electrodes sealing.  FIG. 6A  shows an arc lamp  732  consisting of electrodes  732   c,  sealing  732   a , reflective coating  732   d  and bulb  732   b . The reflective coating  732   d  is first applied to part (or most) of the electrodes  732   c  then the sealing  732   a  is applied.  
         [0081]      FIG. 6B  shows the application of the reflective coating  732   e  to the cross sections of the electrodes  732   c.    FIG. 6C  shows the extension  732   f  of the electrodes sealing.  FIG. 6D  shows a cross-sectional view in xz-plane of a collection system  832  using the arc lamp  732  and a tunnel with a cross section  732   g  (the collimating plate is not shown).  
         [0082]     The collection system  832  has the advantage of reducing radiation absorption by the electrodes and preventing radiation from exiting the collection system through the electrodes sealing.  FIG. 6E  shows a cross-sectional view in xz-plane of a collection system  932  using a tunnel with a smaller cross section  932   g  (the collimating plate is not shown). This size reduction is achieved by moving the reflective coating  732   e  closer to the bulb  732   b . This collection system  932  has the advantage of reducing the optical extent of delivered radiation.  FIG. 6F  shows a cross-sectional view in xz-plane of a collection system  1032  (the collimating plate is not shown) utilizing a bulb  1032   b  of a cylindrical shape.  
         [0083]      FIG. 7  shows a collection and homogenization system  1500  comprises a collimating plate  1534 , tunnel  1533 , source  1532  and an optional solid pipe (or hollow tunnel)  1535 . The short tunnel  1533  permits the conversion of the radiation with high angles (for example, near ±90° with respect to the optical axis or y-axis) to radiation with low angles (for example, near ±30° with respect to the optical axis or y-axis) via the collimating plate  1534  while reducing the absorption losses of high angled radiation at the tunnel&#39;s  1533  reflective sidewalls due to the reduction in its length. Optional tunnel  1535  receives radiation from collimating plate  1534  and delivers a more homogenous and uniform spatial distribution of radiation. The advantage of the system  1500  over collection systems  30 ,  130 ,  230 ,  330 , and  430  is its lower losses.  
         [0084]     A collection system  1600  suitable for an electrodeless lamp excited by microwave energy is shown in  FIG. 8 . The collection system  1600  comprises a collimating plate  1634 , tunnel  1633  and electrodeless lamp  1632 . The collimating plate  1634  as well as the tunnel&#39;s  1633  sidewalls and backside and/or associated film coatings should be formed from materials which block the leakage of the microwave energy and pass light through the collimating plate&#39;s  1634  entrance aperture. For example, it is possible to have collimating plate  1634  and tunnel&#39;s  1633  sidewalls and backside made from a material (e.g., glass and quartz) that does not block microwave, but is coated with a film that blocks microwave energy. In addition, the aperture plate (which is part of the collimating plate  1634 ) as well as the tunnel&#39;s  1633  sidewalls and backside have to be coated with a highly reflective coating (specular or diffuse) in order block the leakage of light. It is preferable in some cases to block UV and IR radiations as well. U.S. Pat. No. 6,734,638 B 2  to Hyung Joo Kang et al., U.S. Pat. No. 6,873,119 B 2  to Jin-Joong Kim et al. and U.S. Pat. No. 6,791,270 B2 to Hyun Jung Kim et al., all of which are hereby incorporated by reference, provide examples of electrodeless microwave lamps that can be used in connection with the collection system  1600  presented in this patent.  
         [0085]     A collection system  1700  suitable for an electrodeless lamp excited by high frequency electromagnetic energy is shown in  FIG. 9 . This collection system  1700  consists of a collimating plate  1734 , tunnel  1733  and electrodeless lamp  1732 . The tunnel&#39;s  1733  sidewalls and their coatings should be formed from materials which pass high frequency electromagnetic energy and block leakage of light. The tunnel&#39;s backside and collimating plate can be made from material that can block high frequency electromagnetic energy. U.S. Pat. No. 5,498,928 to Walter P. Lapatovich et al., which is hereby incorporated by reference, provides an example of electrodeless lamp excited by high frequency electromagnetic energy that can be used in connection with the collection system  1700  presented in this patent.  
         [0086]     The reflective coating can be a metallic coating, dielectric coating, cold mirror coating, dichroic mirror coating, specular, diffuse or a combination of these. Tunnel  33  can be straight, tapered, cylindrical, square, rectangular, or spherical. Length of light guide ranges from few millimeters to tens of millimeters depending on the source size, size of tunnel&#39;s entrance and exit apertures, cone angle of radiation propagating within the tunnel  33  and degree of desired radiation uniformity delivered by the collection system  30 ,  130 ,  230 ,  330 ,  430 ,  530 ,  630 ,  832 ,  932 ,  1032  and  1500 . The entrance and exit faces of tunnel  33 ,  33   a ,  333   b ,  433   a ,  433   b ,  732   g,    932   g,    1032   g,    1533 , and  1535  are independent in terms of size and shape and can have different sizes and different shapes such as square, rectangular, circular, trapezoidal, polygonal, asymmetrical and even irregular shapes. The tunnel sidewalls and backside can be made of materials such as glass, fused silica, quartz, metal, ceramic, and alumina. Metallic materials have good thermal conductivity and are preferable in case of electrodeless lamps of the microwave type where maintaining the microwave energy around the bulb is required.  
         [0087]     While one or more specific embodiments of the invention have been described above, it will be apparent to those of ordinary skill in the art that many more embodiments are possible that are within the scope of the invention. Further, the foregoing summary, detailed description and drawings are considered as illustrative only of the principles of the invention. Since other modifications and changes may be or become apparent to those skilled in the art, the invention is not limited the exact constructions and operations shown and described above, and accordingly, all suitable modifications and equivalents are deemed to fall within the scope of the invention, the invention being defined by the claims that follow.