Patent Publication Number: US-2009237958-A1

Title: Low-clearance light-emitting diode lighting

Description:
BACKGROUND OF THE INVENTION 
     1. Field of The Invention 
     The present invention relates to lighting, and more particularly, to low-clearance light-emitting diode lighting. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for providing low-clearance light-emitting diode lighting for either drop-ceilings, drywall/plaster ceilings or walls. 
     2. Discussion Of The Related Art 
     In general, drop-ceilings are typically installed in commercial buildings. However, drop-ceilings can also be installed in residences, such as during basement remodeling.  FIG. 1A  is a perspective view of a drop-ceiling having ceiling-grid with a lighting unit according to the related art. As shown in  FIG. 1A , horizontal rails  1   a  and vertical rails  1   b  create a ceiling-grid  1  with openings in which ceiling tiles  2  is positioned. The ceiling-grid  1  shown in  FIG. 1A  is, for example, a two foot by two foot ceiling-grid. As also shown in  FIG. 1A , the related art lighting unit  3 , such as a fluorescent lighting fixture, can also be positioned in the ceiling-grid  1 . The related art lighting unit  3  has the same standard size or outside dimensions as the ceiling tiles  2 . 
     Drop-ceilings are easy to install because the ceiling-grid can be hung by wire-hangers, which can be readily attached to the overhead ceiling. The use of the wire-hangars permits simple installation and leveling of the drop-ceiling. A drop-ceiling covers up the electrical wires, ventilation equipment and plumbing that can run along an overhead ceiling. The electrical wires, ventilation equipment and plumbing above the drop-ceiling are easy to access through the ceiling-grid after removal of the ceiling tiles. However, a drop-ceiling requires a minimum clearance between the overhead ceiling and the drop-ceiling. 
       FIG. 1B  is a cross-sectional view of a ceiling having ceiling-grid with a lighting unit along the line I-I′ of  FIG. 1A . As shown in  FIG. 1B , the back of the related art lighting unit  3 , which resides in an opening of the ceiling-grid  1 , extends from the ceiling-grid  1  to a lighting unit height HLU above the ceiling-grid  1 . The lighting unit height HLU above the ceiling-grid  1  can be about five to six inches, depending on the depth D of the related art lighting unit  3 . A minimum insertion height HMI is needed in addition to the lighting unit height HLU so as to be able to insert the related art lighting unit  3  into the ceiling-grid  1 . The minimum insertion height HMI of the related art lighting unit  3  can be about four to six inches. Thus, the minimal lighting clearance height HMLC that a drop-ceiling must have to receive the related art lighting unit is the sum of the lighting unit height HLU and the minimum insertion height HMI, as shown in  FIG. 1  B. Accordingly, the minimal lighting clearance height HMLC that a drop-ceiling must have to receive the related art lighting unit can be about nine to twelve inches. 
     Typically, the minimum clearance between an overhead ceiling and a drop-ceiling is limited by the minimal lighting clearance height HMLC of the related art lighting unit. Thus, the minimal lighting clearance height HMLC of the related art lighting unit dictates the drop-ceiling height HDC over the floor, as shown in  FIG. 1B . In other words, the maximum drop-ceiling height HDC is usually limited by the minimal lighting clearance height HMLC. 
     Unlike drop-ceilings, a drywall/plaster ceiling is attached directly to either roof joists or floor joists. The related art lighting units in drywall/plaster ceilings are placed between the joists to accommodate the lighting unit height HLU of the related art lighting units. However, the size of the related art lighting units is limited to the spacing between floor/ceiling joists. Further, the placement of related art lighting units in a drywall/plaster ceiling is restricted because of the need for the related art lighting units to be placed between floor/ceiling joists. 
     Although the lighting efficiency of a light-emitting diode lighting fixture is high, heat is generated by the light-emitting diodes of a light-emitting diode lighting fixture. Removal or dissipation of such heat away from the light-emitting diodes is a determining factor in both the efficiency and the overall durability of the light-emitting diodes. However, the positioning of the light-emitting diodes may not be conducive to efficient use of the light emanating from the light-emitting diodes. Further, the addition of structures for efficient thermal dissipation may detract from the aesthetics of the fixture and impede implementation of the fixture. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to low-clearance lighting that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide light-emitting diode lighting with low overhead clearance. 
     Another object of the present invention is to improve the thermal dissipation capability of light-emitting diode lighting. 
     Another object is to provide light-emitting diode lighting configured to reside in ceiling-grids with low overhead clearance. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, a low-clearance light-emitting diode lighting includes a light guide panel having side surfaces and a front surface opposing a back surface, a plurality of light-emitting diodes positioned on at least two side surfaces of the light guide panel, a reflecting plate at the back surface of the light guide panel, reflectors having an inclined angle, and a metal frame for supporting the reflecting plate and the light guide panel, wherein each of the plurality of light-emitting diodes is positioned between one of the at least two side surfaces and one of the reflectors such that light from the plurality of light-emitting diodes is reflected toward the at least two side surfaces. 
     In another aspect, a low-clearance light-emitting diode lighting includes a light guide panel having side surfaces and a front surface opposing a back surface, a plurality of light-emitting diodes positioned on at least two side surfaces of the light guide panel, and a reflective encasement having an interior reflective surface at back surface of the light guide panel and interior reflective surfaces having an inclined angle, wherein each of the plurality of light-emitting diodes is positioned between one of the at least two side surfaces and one of the inclined interior reflective surfaces such that light from the plurality of light-emitting diodes is reflected toward the at least two side surfaces. 
     In another aspect, a low-clearance light-emitting diode lighting includes a light guide panel having side surfaces and a front surface opposing a back surface, a reflecting plate at the back surface of the light guide panel, reflectors having an inclined angle, and a plurality of light-emitting diodes positioned on at least two side surfaces of the light guide panel and mounted on the reflecting plate, wherein each of the plurality of light-emitting diodes is positioned between one of the at least two side surfaces and one of the reflectors such that light from the plurality of light-emitting diodes is reflected toward the at least two side surfaces. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1A  is a perspective view of a lighting unit in the ceiling-grid of a drop-ceiling according to the related art; 
         FIG. 1B  is a cross-sectional view along the line I-I′ of  FIG. 1A ; 
         FIG. 2A  is a perspective view of a ceiling-grid with a low-clearance light-emitting diode lighting unit according to embodiments of the invention; 
         FIG. 2B  is a cross-sectional view along the line II-II′ of  FIG. 2A ; 
         FIG. 3  is a top view of a low-clearance light-emitting diode lighting unit shown in  FIGS. 2A-2B ; 
         FIG. 4A  is a side view of the light tile shown in  FIG. 3  according to a first embodiment of the invention; 
         FIG. 4B  is an exploded view of the circle III shown in  FIG. 4A ; 
         FIG. 5A  is a side view of the light tile shown in  FIG. 3  according to a second embodiment of the invention; 
         FIG. 5B  is an exploded view of the circle IV shown in  FIG. 5A ; 
         FIG. 6A  is a cross-sectional view of a low-clearance light-emitting diode lighting unit according to a third embodiment of the invention; 
         FIG. 6B  is an exploded view of the circle V shown in  FIG. 6A ; 
         FIG. 7A  is a cross-sectional view of a low-clearance light-emitting diode lighting unit according to a fourth embodiment of the invention; 
         FIG. 7B  is an exploded view of the circle VI shown in  FIG. 6A ; 
         FIG. 8A  is a perspective view of a drywall/plaster ceiling having a low-clearance light-emitting diode lighting unit according to a fifth embodiment of the invention; 
         FIG. 8B  is a cross-sectional view of along the line VII-VII′ of  FIG. 8A ; 
         FIG. 9A  is a bottom view of a circular LED lighting fixture; 
         FIG. 9B  is a side view of the circular LED lighting fixture shown in  FIG. 9A ; 
         FIG. 10  is a hexagonal-shaped low-clearance light-emitting diode lighting unit according to a sixth embodiment of the invention; and 
         FIG. 11  is a trapezoidal-shaped low-clearance light-emitting diode lighting unit according to a seventh embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like reference numerals in the drawings denote like elements. 
       FIG. 2A  is a perspective view of a ceiling-grid with a low-clearance light-emitting diode lighting unit according to a first embodiment of the invention. As shown in  FIG. 2A , horizontal rails  10   a  and vertical rails  10   b  create a ceiling-grid  10  having openings in which ceiling tiles  20  are positioned. The ceiling-grid  10  shown in  FIG. 2A  is, for example, a two foot by two foot ceiling-grid  10 . As also shown in  FIG. 2A , a low-clearance light-emitting diode lighting unit  30  is positioned in an opening of the ceiling-grid  10 . The low-clearance light-emitting diode lighting unit  30  has a similar size or outside dimensions as the ceiling tiles  20 . Although a two foot by two foot ceiling-grid  10  is shown in  FIG. 2A , embodiments of the invention can be implemented in two foot by four foot grid as well as grids of other sizes. 
       FIG. 2B  is a cross-sectional view of a ceiling-grid with a lighting unit along the line II-II′ of  FIG. 2A . As shown in  FIG. 2B , the low-clearance light-emitting diode lighting unit  30 , which resides in an opening of the ceiling-grid  10 , may extend above the ceiling-grid  10  because of a power supply  36  mounted at the back of the low-clearance light-emitting diode lighting unit  30 . Further, the low-clearance light-emitting diode lighting unit  30  may have profile such that a portion of the low-clearance light-emitting diode lighting unit  30  protrudes slightly with a protrusion distance DPCG from the ceiling-grid  10 . 
     As shown in  FIG. 2B , the low-clearance light-emitting diode lighting unit  30  has a minimum insertion height HMILED so as to be able to insert the low-clearance light-emitting diode lighting unit  30  into the ceiling-grid  10 . The minimum insertion height HMILED can be about one to three inches for a light-emitting diode lighting unit  30  without a power supply and about two to four inches for light-emitting diode lighting unit  30  with a power supply. Thus, the minimal lighting clearance height that a drop-ceiling must have to receive the low-clearance light-emitting diode lighting unit  30  is just the minimum insertion height HMILED of the low-clearance light-emitting diode lighting unit  30 . The low-clearance light-emitting diode lighting unit of embodiments of the invention can increase the height between the floor and the low-clearance light-emitting diode lighting unit so as to raise a drop-ceiling by decreasing the lighting clearance height to about two to four inches. 
       FIG. 3  is a top view of a low-clearance light-emitting diode lighting unit shown in  FIGS. 2A-2B . As shown in  FIG. 3 , a light guide panel  38  is surrounded by a frame  43 . A first set of light-emitting diodes  37   a  is positioned on one side of the low-clearance light-emitting diode lighting unit within the frame  43  and a second set of light diodes  37   b  is position at a second side of the low-clearance light-emitting diode lighting unit  33  within the frame  43 . The first and second sets of light-emitting diodes  37   a  and  37   b  can be on opposite sides of the low-clearance light-emitting diode lighting unit. Although the first and second sets of light-emitting diodes  37   a  and  37   b  are shown directly opposing each other in  FIG. 3 , the first and second sets of light-emitting diodes  37   a  and  37   b  can be on opposite sides of the low-clearance light-emitting diode lighting unit but yet offset from one another. Further, an additional set or sets of light-emitting diodes can be provided at another side or other sides of the low-clearance light-emitting diode lighting unit for increased light output. 
       FIG. 4A  is a side view of the light tile shown in  FIG. 3  according to a first embodiment of the invention. As shown in  FIG. 4A , a low-clearance light-emitting diode lighting unit can include a light guide panel  38  for receiving light from the side light-emitting diodes  37   a  and  37   b  and then distributing the light across the front surface  38   a  of the light guide panel  38 . A reflective plate  40  on the back surface  38   b  of the light guide panel  38  reflects light toward the front surface  38   a  of the light guide panel  38 . The side light-emitting diodes  37   a  and  37   b  are mounted on the reflective plate  40  within the frame  43 . Reflectors  40   a  and  40   b , which are an integral part of the reflective plate  40 , reflect light from the side light-emitting diodes  37   a  and  37   b  toward the two side surfaces  38   c  and  38   d  of the light guide panel  38 . Finned heatsinks  45   a  and  45   b  are mounted on the frame  43  adjacent to the side light-emitting diodes  37   a  and  37   b  to dissipate heat generated by the side light-emitting diodes  37   a  and  37   b . Heat dispersers  44   a  and  44   b  between the side light-emitting diodes  37   a  and  37   b  and the frame  43  increase thermal transfer from the light-emitting diodes  37   a  and  37   b  to the finned heatsinks  45   a  and  45   b . A diffusion film  42  can be positioned directly on the front surface  38   a  of the light guide panel  38  to increase light dispersion. A power supply  36  can be mounted on the reflective plate  40  under the back surface  38   b  of the light guide panel  38  for converting 120 VAC to 12 VDC to drive the side light-emitting diodes  37   a  and  37   b.    
     The side light-emitting diodes  37   a  and  37   b  can be white light-emitting diodes. In the alternative, the side light-emitting diodes  37   a  and  37   b  can include red, blue and green light-emitting diodes that are positioned along the sides of the light guide panel  38  such that the red, blue and green lights from the red, blue and green light-emitting diodes combines into white light. In another alternative, the side light-emitting diodes  37   a  and  37   b  can be blue light-emitting diodes. In yet another alternative, the side light-emitting diodes  37   a  and  37   b  can be ultraviolet light-emitting diodes. In the cases of blue light-emitting diodes and ultraviolet light-emitting diodes, a color conversion structure is needed to convert the blue light or the ultraviolet light into white light. 
     As shown in  FIG. 4A , a pair of color conversion films  41   a  and  41   b  can be positioned at the two side surfaces  38   c  and  38   d  of the light guide panel  38 . More specifically, the pair of color conversion films  41   a  and  41   b  can be positioned between the two side surfaces  38   c  and  38   d  of the light guide panel  38  and the side light-emitting diodes  37   a  and  37   b . The color conversion films  41   a  and  41   b  can convert ultraviolet light or blue light from the side light-emitting diodes  37   a  and  37   b  to white light. 
     The side light-emitting diodes  37   a  and  37   b  can be configured to emit light in 360 degrees or emit light in two opposing 90 degree arcs. If the side light-emitting diodes  37   a  and  37   b  are configured to emit light in two opposing 90 degree arcs, one of the arcs is centered on one of the at least two side surfaces  38   c  and  38   d  of the light guide panel  38 . In the alternative, the top light-emitting diodes  37   a  and  37   b  can be used that emit light directly toward the reflectors  40   a  and  40   b.    
       FIG. 4B  is an exploded view of the circle III shown in  FIG. 4A . As shown in  FIG. 4B , the reflector  40   b  is at an angle θ1 of inclination with respect to the reflective plate  40 . The angle θ1 can be within a range of thirty to eighty-five degrees. The angle θ1 of inclination tends to be greater for side light-emitting diodes than top light-emitting diodes. Since the light-emitting diode  37   b  is a side light-emitting diode and the reflector  40   b  is at an angle Θ1 with respect to the reflective plate  40 , a first light L 4  and L 5  is emitted directly toward the side surface  38   d  of the light guide panel  38  from the side light-emitting diode  37   b  while a second light L 2  is reflected from the reflector  40   b  toward the side surface  38   d  of the light guide panel  38 . 
     As shown in  FIG. 4B , a finned heatsink  45   b  is positioned directly under and adjacent to the light-emitting diode  37   b  on the underside of the frame  43 . Heat from the light-emitting diode  37   b  is transferred through the reflective plate  40  and the frame  43  to the finned heatsink  45   b . To increase the thermal efficiency of heat transfer from the side light-emitting diode  37   b , a heat disperser  44   b  can be positioned between light-emitting diode  37   b  and the reflective plate  40 . The heat disperser  44   b  can be made of a thermally conductive, such as copper, aluminum or steel, and can be in the form of a strip on which a plurality of the side light-emitting diodes  37   b  are mounted. 
       FIG. 5A  is a side view of the light tile shown in  FIG. 3  according to a second embodiment of the invention. As shown in  FIG. 5 , a low-clearance light-emitting diode lighting unit can include a light guide panel  38  for receiving light from the side light-emitting diodes  37   a  and  37   b  and then distributing the light across the front surface  38   a  of the light guide panel  38 . A reflective plate  50  on the back surface  38   b  of the light guide panel  38  reflects light toward the front surface  38   a  of the light guide panel  38 . The side light-emitting diodes  37   a  and  37   b  are mounted within the frame  43 . Reflectors  49   au  and  49   bu  reflect light from the side light-emitting diodes  37   a  and  37   b  toward the two side surfaces  38   c  and  38   d  of the light guide panel  38 . Finned heatsinks  45   a  and  45   b  are mounted on the frame  43  adjacent to the side light-emitting diodes  37   a  and  37   b  to dissipate heat generated by the side light-emitting diodes  37   a  and  37   b . Heat dispersers  49   a 1   and  49   b 1   between the side light-emitting diodes  37   a  and  37   b  and the frame  43  increase thermal transfer from the side light-emitting diodes  37   a  and  37   b  to the finned heatsinks  45   a  and  45   b . A diffusion film  42  can be positioned directly on the front surfaces  38   a  of the light guide panel  38  to increase light dispersion. A power supply  36  can be mounted on the reflective plate  50  under the back surface  38   b  of the light guide panel  38  for converting 120 VAC to 12 VDC to drive the side light-emitting diodes  37   a  and  37   b.    
       FIG. 5B  is an exploded view of the circle IV shown in  FIG. 5A . As shown in  FIG. 5B , the reflector  49   bu  is at an angle θ2 of inclination with respect to the heat disperser  49   b 1   . The angle θ2 can be within a range of thirty to eighty-five degrees. The angle θ2 of inclination tends to be greater for side light-emitting diodes than top light-emitting diodes. Since the light-emitting diode  37   b  is a side light-emitting diode and the reflector  49   bu  is at an angle θ2 with respect to the heat disperser  49   b 1   , a first light L 4  and L 5  is emitted directly toward the side surface  38   d  of the light guide panel  38  from the side light-emitting diode  37   b  while a second light L 2  is reflected from the reflector  49   bu  toward the side surface  38   d  of the light guide panel  38 . 
     As shown in  FIG. 5B , a finned heatsink  45   b  is positioned directly under and adjacent to the light-emitting diode  37   b  on the underside of the frame  43 . Heat from the side light-emitting diode  37   b  is transferred through the frame  43  to the finned heatsink  45   b . To increase the thermal efficiency of heat transfer from the side light-emitting diode  37   b , a heat disperser  49   b 1   can be positioned between side light-emitting diode  37   b  and the frame  43 . The heat disperser  49   b 1   can be made of a thermally conductive, such as copper, aluminum or steel, and can be in the form of a strip on which a plurality of the side light-emitting diodes  37   b  are mounted. The reflector  49   bu  can be an integral part of the heat disperser  49   b 1   . As shown in  FIG. 5B , the reflector  49   bu  is separate from the reflective plate  50 . 
     The first and second embodiments of the invention shown in  FIGS. 4A ,  4 B,  5 A and  5 B have a frame for attaching the reflective plate, light guide panel and the diffusion film together. In both the first and second embodiments, the reflectors are within the frame. Third and fourth embodiments of the invention include an encasement, which is both a reflective plate and reflectors, attaching the light guide panel and the diffusion film together such that the interior surface of the encasement is a reflector for the light guide panel and the light-emitting diodes mounted on the encasement. 
       FIG. 6A  is a cross-sectional view of a low-clearance light-emitting diode lighting unit according to a third embodiment of the invention. As shown in  FIG. 6A , a low-clearance light-emitting diode lighting unit can include a light guide panel  38  for receiving light from the side light-emitting diodes  37   a  and  37   b  and then distributing the light across the front surface  38   a  of the light guide panel  38 . An encasement  51  includes a back reflector part  51 B having an interior reflective surface at back surface  38   b  of the light guide panel  38  that reflects light toward the front surface  38   a  of the light guide panel  38  and side reflectors  51 S having an interior reflective surfaces that reflect light from the side light-emitting diodes  37   a  and  37   b  toward the two side surfaces  38   c  and  38   d  of the light guide panel  38 . Finned heatsinks  45   a  and  45   b  are mounted on the encasement  51  adjacent to the side light-emitting diodes  37   a  and  37   b  to dissipate heat generated by the side light-emitting diodes  37   a  and  37   b . Heat dispersers  44   a  and  44   b  between the side light-emitting diodes  37   a  and  37   b  and the encasement  51  increase thermal transfer from the side light-emitting diodes  37   a  and  37   b  to the finned heatsinks  45   a  and  45   b . A color conversion film  53  can be positioned directly on the front surface  38   a  of the light guide panel  38  to convert blue or ultraviolet light from the side light-emitting diodes  37   a  and  37   b  into white light. A diffusion film  42  can be positioned directly on the color conversion film  53  to increase light dispersion. A power supply  36  can be mounted on the encasement  51  under the back surface  38   b  of the light guide panel  38  for converting 120 VAC to 12 VDC to drive the side light-emitting diodes  37   a  and  37   b.    
       FIG. 6B  is an exploded view of the circle V shown in  FIG. 6A . As shown in  FIG. 6A , the side reflector  51 S of the encasement  51  is at an angle θ3 of inclination with respect to the back reflector part  51 B of the encasement  51 . The angle θ3 can be within a range of thirty to eighty-five degrees. Since the light-emitting diode  37   b  is a side light-emitting diode and the side reflector  51 S of the encasement  51  is at an angle θ3 with respect to the back reflector part  51 B of the encasement  51 , a first light L 4  and L 5  is emitted directly toward the side surface  38   d  of the light guide panel  38  from the side light-emitting diode  37   b  while a second light L 2  is reflected from the side reflector  51 S, which is an interior side surface of the encasement  51 , toward the side surface  38   d  of the light guide panel  38 . 
     As shown in  FIG. 6B , a finned heatsink  45   b  is positioned directly under and adjacent to the side light-emitting diode  37   b  on the underside the back reflector part  51 B of the encasement  51 . Heat from the side light-emitting diode  37   b  is transferred through the back reflector part  51 B of the encasement  51  to the finned heatsink  45   b . To increase the thermal efficiency of heat transfer from the side light-emitting diode  37   b , a heat disperser  44   b  can be positioned between side light-emitting diode  37   b  and the back reflector part  51 B of the encasement  51 . The heat disperser  44   b  can be made of a thermally conductive, such as copper, aluminum or steel, and can be in the form of a strip on which a plurality of the side light-emitting diodes  37   b  are mounted. As shown in  FIG. 6B , the side reflector  51 S is integral with the back reflector part  51 B. 
       FIG. 7A  is a cross-sectional view of a low-clearance light-emitting diode lighting unit according to a fourth embodiment of the invention. As shown in  FIG. 7A , a low-clearance light-emitting diode lighting unit can include a light guide panel  38  for receiving light from the top light-emitting diodes  67   a  and  67   b  and then distributing the light across the front surface  38   a  of the light guide panel  38 . An encasement  61  includes a back reflector part  61 B having an interior reflective surface at back surface  38   b  of the light guide panel  38  that reflects light toward the front surface  38   a  of the light guide panel  38  and side reflectors  61 S having interior reflective surfaces that reflect light from the top light-emitting diodes  67   a  and  67   b  toward the two side surfaces  38   c  and  38   d  of the light guide panel  38 . Finned heatsinks  45   a  and  45   b  are mounted on the encasement  61  adjacent to the top light-emitting diodes  67   a  and  67   b  to dissipate heat generated by the top light-emitting diodes  67   a  and  67   b . Heat dispersers  44   a  and  44   b  between the top light-emitting diodes  67   a  and  67   b  and the encasement  61  increase thermal transfer from the top light-emitting diodes  67   a  and  67   b  to the finned heatsinks  45   a  and  45   b . A color conversion film  53  can be positioned directly on the front surface  38   a  of the light guide panel  38  to convert blue or ultraviolet light from the top light-emitting diodes  67   a  and  67   b  into white light. A diffusion film  42  can be positioned directly on the color conversion film  53  to increase light dispersion. A power supply  36  can be mounted on the encasement  61  under the back surface  38   b  of the light guide panel  38  for converting 120 VAC to 12 VDC to drive the top light-emitting diodes  67   a  and  67   b.    
       FIG. 7B  is an exploded view of the circle VI shown in  FIG. 6A . As shown in  FIG. 7A , the side reflector  61 S of the encasement  61  is at an angle θ4 of inclination with respect to the back reflector part  61 B of the encasement  61 . The angle θ4 can be within a range of twenty to sixty degrees. The interior surface of the side reflector  61 S of the encasement  61  has a convex shape. Since the light-emitting diode  67   b  is a top light-emitting diode and the convex-shaped side reflector  61 S of the encasement  61  is at an angle θ4 with respect to the back reflector part  61 B of the encasement  61 , light L 3  is reflected from the side reflector  61 S so that the reflected light L 3  spreads out toward the side surface  38   d  of the light guide panel  38 . 
     As shown in  FIG. 7B , a finned heatsink  45   b  is positioned directly under and adjacent to the top light-emitting diode  67   b  on the underside the back reflector part  61 B of the encasement  61 . Heat from the top light-emitting diode  67   b  is transferred through the back reflector part  61 B of the encasement  61  to the finned heatsink  45   b . To increase the thermal efficiency of heat transfer from the top light-emitting diode  67   b , a heat disperser  44   b  can be positioned between the top light-emitting diode  67   b  and the back reflector part  61 B of the encasement  61 . The heat disperser  44   b  can be made of a thermally conductive, such as copper, aluminum or steel, and can be in the form of a strip on which a plurality of the top light-emitting diodes  67   b  are mounted. As shown in  FIG. 7B , the side reflector  61 S is integral with the back reflector part  61 B. 
       FIG. 8A  is a perspective view of a drywall/plaster ceiling having a low-clearance light-emitting diode lighting unit according to a fifth embodiment of the invention. As shown in  FIG. 8A , ceiling joists  101  support a ceiling  110 , such as a drywall or plaster ceiling. As also shown in  FIG. 8A , a low-clearance light-emitting diode lighting unit  130  is mounted on the ceiling  110 . A trim piece cover  133  about the periphery of the low-clearance light-emitting diode lighting unit  130  covers the mounting hardware  132 . 
       FIG. 8B  is a cross-sectional view of along the line VII-VII′ of  FIG. 8A . As shown in  FIG. 8B , the mounting hardware  132  can include a bracket  131  and a lag screw  132 . The bracket  131  is positioned on the light-emitting diode lighting unit  130 , and then the lag screw  132  goes through bracket  131  into a joist  101  so as to attach the low-clearance light-emitting diode lighting unit  130  to the ceiling  110 . The low-clearance light-emitting diode lighting unit  130  can be attached to two ceiling joists  101  through the ceiling  110 , as shown in  FIG. 8B . Alternatively, the low-clearance light-emitting diode lighting unit  130  can be attached to just one ceiling joist. Further, the low-clearance light-emitting diode lighting unit  130  could just be attached directly to the ceiling  110 . 
     Although the fifth embodiment of the invention is described with regard to mounting a low-clearance light-emitting diode lighting unit on a ceiling, the low-clearance light-emitting diode lighting unit of the fifth embodiment can also be mounted on a wall. Instead of ceiling joists, the low-clearance light-emitting diode lighting unit of the fifth embodiment can be attached to the wall studs of a wall or just directly attached to a wall. Further, the low-clearance light-emitting diode lighting unit of the fifth embodiment can be mounted directly on the ceiling joists such that the low-clearance light-emitting diode lighting unit of the fifth embodiment is slightly recessed into the ceiling. Furthermore, the low-clearance light-emitting diode lighting unit of the fifth embodiment can be mounted directly on the wall studs such that the low-clearance light-emitting diode lighting unit of the fifth embodiment is slightly recessed into the wall. 
     The low-clearance light-emitting diode lighting unit  130  shown in  FIG. 8B  only has a protrusion distance DPC from the ceiling of about one to three inches. Thus, the low-clearance light-emitting diode lighting unit  130  can be mounted on a ceiling  110  without significantly affecting the overall height between the floor and the low-clearance light-emitting diode lighting unit  130 . The low-clearance light-emitting diode lighting unit of the fifth embodiment of the invention allows for more freedom in the placement of the lighting unit in that the low-clearance light-emitting diode lighting unit can be mounted anywhere on a ceiling. Further, the low-clearance light-emitting diode lighting unit of the fifth embodiment can be mounted on a wall without significantly protruding from the wall. 
       FIG. 9A  is a bottom view of a circular LED lighting fixture and  FIG. 9B  is a side view of the circular LED lighting fixture shown in  FIG. 9A . As shown in  FIG. 9A , the circular LED lighting fixture  200  has a light guide panel  210  at its center. The light guide panel  210  is surrounded by light emitting diodes  201  that emit light L 4  and L 5  into the light guide panel  210 , as shown in  FIG. 9A . The light guide panel  210  is made from both transparent and partially transparent polymers. As shown in  FIG. 9A  and  FIG. 9B , the light emitting diodes  201  emit light L 4  and L 5  that enters the light guide panel  210  in a radially inward direction. As shown in  FIG. 9A , each light-emitting diode  201  is adjacent to reflector  202 , that redirects light emitted by the light-emitting diode  201  towards the light guide panel  210 . 
     The redirection of light by the reflector  202  is shown in more detail in  FIG. 9B . As shown in  FIG. 9B , light L 5  has been emitted by light-emitting diode  201  and redirected by the reflector  202  towards the light guide panel  210 . Ultimately, the light guide panel  210  redirects light L 4  and L 5  emitted by the light emitting diodes, as shown in  FIG. 9B , out of the circular LED lighting fixture  200  as light L 6 . As also shown in  FIG. 9B , a finned heatsink  201   a  is positioned directly under and adjacent to the light-emitting diode  201 . Heat from the light-emitting diode  201  is transferred to the finned heatsink  201   a . To increase the thermal efficiency of heat transfer from the light-emitting diode  201 , a heat disperser (not shown) can be positioned on the light-emitting diode  201 . The heat disperser (not shown) can be made of a thermally conductive material, such as copper, aluminum or steel, and can be in the form of a strip on which a plurality of the light-emitting diode  201  are mounted. 
     The circular LED lighting fixture  200  of  FIGS. 9A and 9B  has a power supply  211  and fits in the recessed can lighting fixture  220 . The circular LED lighting fixture  200  is circular or disk shaped, as shown in  FIG. 9A  and  FIG. 9B . In the alternative, the LED lighting fixture  200  can have one of a number of other shapes, such as that of an ellipse, polygon or annulus. As shown in  FIG. 9A  and  FIG. 9B , a mirrored top surface  210   a  of the circular LED lighting fixture  200  reflects light L 4  and L 5  emitted by the light emitting diodes  201 . The mirrored top surface  210   a  can be a reflective layer  210   a  that is separate from the light guide panel  210 . Alternatively, the mirrored top surface  210   a  is a reflective layer  210   a  on the light guide panel  210  of a reflective material, such as a metal. The mirrored top surface  210   a  can be opaque and reflective to the light L 4  and L 5  emitted by the light emitting diodes  201 . Alternatively, the mirrored top surface  210   a  is partially transmissive to the light L 4  and L 5  emitted by the light emitting diodes  201 . As shown in  FIG. 9A  and  FIG. 9B , light L 4  and L 5  emitted by the light emitting diodes  201  and reflected from the mirrored top surface  210   a  leaves the circular LED lighting fixture  200  through the bottom surface  210   b  of the circular LED lighting fixture  200  to provide light L 6  below the circular LED lighting fixture  200 . 
     The can  220  is affixed to the ceiling  280  using one of a number of methods that include the use of affixing tabs (not shown). The can  220  is cylindrically shaped, as shown in  FIG. 9A  and  FIG. 9B . Alternatively, the can  220  can have one of a number of different shapes including that of a rectangular prism or a prism with a triangular cross section. The can  220  is made from metal, plastic or a combination thereof. The can  220  includes a socket  206  for supplying power to the circular LED lighting fixture  200  through the power supply  211  received into the socket  206 . The power supply  211  is electrically connected to the socket  206  by inserting it into the socket  206  as shown in  FIG. 9A  and  FIG. 9B . The circular LED lighting fixture  200  is connected to the power supply  211  by connecting the connectors  44  and  55  of the circular LED lighting fixture  200  to the connectors  24  and  25  of the power supply  211 . 
       FIG. 10  is a hexagonal-shaped low-clearance light-emitting diode lighting unit according to a sixth embodiment of the invention. As shown in  FIG. 10 , a first set of light-emitting diodes  235   a  is positioned on one side of the hexagonal-shaped light-emitting diode lighting unit  234 , a second set of light diodes  235   b  is position at a second side of the hexagonal-shaped light-emitting diode lighting unit  234 , and a third set of light diodes  235   c  is position at a third side of the hexagonal-shaped LED lighting unit  234 . Preferably, the first, second, and third sets of light-emitting diodes  235   a ,  235   b  and  235   c  should be on every other side of the hexagonal-shaped light-emitting diode lighting unit  234 . In the alternative, the light-emitting diodes can be just on two opposing sides of the hexagonal-shaped light-emitting diode lighting unit  234 . 
       FIG. 11  is a trapezoidal-shaped low-clearance light-emitting diode lighting unit according to a seventh embodiment of the invention. As shown in  FIG. 11 , a first set of light-emitting diodes  238   a  is positioned on one side of the trapezoidal-shaped light-emitting diode lighting unit  236  and a second set of light diodes  238   b  is position at a second side of the trapezoidal-shaped light-emitting diode lighting unit  236 . Preferably, the first and second sets of light-emitting diodes  238   a  and  238   b  should be on opposite sides of the trapezoidal-shaped light-emitting diode lighting unit  236 . In the alternative, an additional set or sets of light-emitting diodes can be provided at another side or other sides to increase light output from the trapezoidal-shaped light-emitting diode lighting unit  236 . 
     As shown by the exemplary embodiments of  FIGS. 9 and 10 , the light-emitting diode lighting units of embodiments of the invention can be any polygonal shape. Further, the light-emitting diode lighting units of embodiments of the invention can have a circular or an elliptical shape. Furthermore, the light-emitting diode lighting units of embodiments of the invention can have a shape that includes both a linear side and a curved side. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to low-clearance lighting of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.