Abstract:
An inventive heat sink adapted for use with light emitting diode luminaires and other applications comprising: a first layer of carbon graphite in thermal communication with a source of heat and a second layer of aluminum in thermal communication with said first layer. Also disclosed is an inventive troffer including a frame; a printed circuit board mounted within the frame; an array of light emitting diodes mounted on the printed circuit board; a heat sink mounted in parallel with the printed circuit board; and a thermal interface layer disposed between the heat sink and the printed circuit board. In yet another embodiment, the inventive troffer assembly includes plural modules mounted within the frame, each module including: a printed circuit board mounted within the frame; an array of light emitting diodes mounted on the printed circuit board; a heat sink mounted in parallel with the printed circuit board; and a thermal interface layer disposed between the heat sink and the printed circuit board.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This is a nonprovisional application claiming priority from a provisional application entitled Lighting Apparatus, Heat Sinks and Methods of Manufacturing filed May 12, 2010, Ser. No. 61/334,173, (Attorney Docket No. 1011-003). 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to lighting systems. More specifically, the present invention relates to heat sinks for light emitting diode based lighting systems. 
         [0004]    2. Description of the Related Art 
         [0005]    As noted in Wikipedia at http://en.wikipedia.org/wiki/Light-emitting diode a light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for general lighting applications. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness. 
         [0006]    When a light-emitting diode is forward biased (switched on), electrons are able to recombine with electron holes within the device and release energy in the form of photons. This effect is called electroluminescence. The color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. 
         [0007]    With the development of high efficiency and high power LEDs it has become possible to use LEDs in general (i.e., commercial, industrial and other) lighting and illumination applications. LEDs present many advantages over fluorescent and incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. For example, while incandescent lights may be expected to last for 2-3,000 hours and fluorescent lights may be expected to last for 15-20,000 hours, LEDs may be expected to last for 70,000-100,000 hours, however heat and current settings can extend or shorten this time significantly. 
         [0008]    For certain applications, such clean rooms in the semiconductor industry, re- lamping may be quite expensive costing millions, especially in view of the fact that production must typically be stopped throughout the process. For such applications, long life and reliability are critical. However, LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact fluorescent lamp sources of comparable output. Hence, cooling of LEDs may be critically important for some applications. 
         [0009]    Prior attempts to cool LED based lighting systems include various heat extraction designs and pulsing the LEDs. However, these approaches have been costly in the use of aluminum or metal core circuit boards and have been only minimally effective. Hence, a need remains in the art for a less expensive and more effective system or method for extracting heat from large LED arrays used in lighting applications. 
       SUMMARY OF THE INVENTION 
       [0010]    The need in the art is addressed by the system and method of the present teachings. The invention includes an inventive heat sink adapted for use with light emitting diode luminaires and other applications comprising: a first layer of carbon graphite in thermal communication with a source of heat and a second layer of aluminum in thermal communication with said first layer. 
         [0011]    The present teachings provide an inventive troffer including a frame; a printed circuit board mounted within the frame; an array of light emitting diodes mounted on the printed circuit board; a heat sink mounted in parallel with the printed circuit board; and a thermal interface layer disposed between the heat sink and the printed circuit board. 
         [0012]    In yet another embodiment, the inventive troffer assembly includes plural modules mounted within the frame, each module including: a printed circuit board mounted within the frame; an array of light emitting diodes mounted on the printed circuit board; a heat sink mounted in parallel with the printed circuit board; and a thermal interface layer disposed between the heat sink and the printed circuit board. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIGS. 1 and 2  are top and bottom views respectively of a troffer assembly according to a first illustrative embodiment of the present invention. 
           [0014]      FIG. 2   a  is an alternative embodiment of the troffer assembly of  FIG. 2  wherein the extruded fins are omitted from the heat sink. 
           [0015]      FIGS. 3 and 4  are top and bottom views respectively of a lighting apparatus comprising the troffer assembly of  FIGS. 1 and 2 . 
           [0016]      FIG. 3   a  is an exploded view of the heat sink assembly of  FIGS. 1-3 . 
           [0017]      FIG. 5  is a perspective view of a first segment of a heat sink that could be incorporated into the troffer assembly of  FIGS. 1 and 2 . 
           [0018]      FIG. 5   a  is a magnified view of a portion of the heat sink segment depicted in  FIG. 5 . 
           [0019]      FIG. 6  is a perspective view of a second segment of a heat sink that could be incorporated into the troffer assembly of  FIGS. 1 and 2 . 
           [0020]      FIG. 6   a  is a magnified view of a portion of the second segment depicted in  FIG. 6 . 
           [0021]      FIG. 7  is a perspective view of an assembled heat sink comprising the first and second segments of  FIGS. 5 and 6 . 
           [0022]      FIG. 7   a  is a magnified view of a portion of the heat sink depicted in  FIG. 7 . 
           [0023]      FIG. 8  is a detailed schematic of the heat sink of  FIG. 7 . 
           [0024]      FIGS. 9 and 10  are top and bottom views respectively of a troffer assembly according to a second embodiment of the present invention. 
           [0025]      FIG. 11  is a side view of a lighting apparatus comprising the troffer assembly of  FIGS. 9 and 10 . 
           [0026]      FIGS. 12 and 13  are perspective views of first and second segments respectively of a heat sink that could be incorporated into the troffer assembly of  FIGS. 9 and 10 . 
           [0027]      FIGS. 12   a  and  13   a  are magnified views of portions of the segments depicted in  FIGS. 12 and 13  respectively. 
           [0028]      FIG. 14  is a perspective view of an assembled heat sink comprising the first and second segments of  FIGS. 12 and 13 . 
           [0029]      FIG. 14   a  is a magnified view of a portion of the assembled heat depicted in  FIG. 14 . 
           [0030]      FIG. 15  is a detailed schematic of the heat sink of  FIG. 14 . 
           [0031]      FIG. 16  shows an alternative embodiment in which the troffer assembly includes four modules instead of one. 
           [0032]      FIG. 17  is a perspective view showing the completed lighting assembly. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0033]    Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the advantageous teachings of the present invention. 
         [0034]    While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility. 
         [0035]    The present invention is directed to lighting apparatus using a troffer assembly, heat sinks and methods of manufacturing lighting apparatus and heat sinks. In embodiments of the present invention, the lighting apparatus is designed as a light emitting diode (LED) luminaire that can replace traditional fluorescent-based troffers that are often implemented as recessed down lights in offices and schools. In particular designs, the troffer assembly has dimensions that can allow for direct replacement of troffers that are implemented with sockets for fluorescent light bulbs. 
         [0036]      FIGS. 1 and 2  are top and bottom views respectively of a troffer assembly according to a first embodiment of the present invention. As shown, the troffer assembly comprises a frame  10  having four sides that form an edge of a container with front and back square planar sides. The front and back planar sides of the container each have a hole that is substantially the size of the respective planar sides, hence leaving both planar sides open with the frame  10  only forming the outside edge of the container. 
         [0037]    The troffer assembly, as shown in  FIGS. 1 and 2 , further comprises a heat sink  12  connected to the frame  10  at the back planar side of the container. In this embodiment, the heat sink  12  has a planar dimension substantially similar to the dimension of the hole in the back planar side of the container. The heat sink is connected to the frame  10  along the edge of the hole in the back planar side of the container such that the hole is fully covered. The heat sink  12  may be connected to the frame  10  with a series of screws or alternatively another fastening mechanism (ex. interlocking connection, clips, snap connection, affixing agent etc.). 
         [0038]    As shown in  FIGS. 1 and 2 , the heat sink  12  comprises first and second planar sides. The first planar side of the heat sink  12  is a flat surface and forms an interior side of the container. When the lighting apparatus according to embodiments of the present invention is assembled, one or more light engine modules (not shown) comprising LEDs are both physically and thermally coupled to the first planar side of the heat sink  12 . 
         [0039]    In the illustrative embodiment of  FIGS. 1 and 2 , the second planar side of the heat sink  12  comprises a plurality of fins  13  and forms an exterior side of the container. The fins on the second planar side of the heat sink  12  provide additional surface area for heat within the heat sink to be dispersed through passive air-cooling. In the case shown in  FIG. 2 , there are numerous narrow longitudinal fins that are substantially perpendicular with the second planar side of the heat sink  12 . It should be understood that in other embodiments other implementations for increasing the surface area of the heat sink  12  and/or other cooling techniques may be used within the heat sink  12 . 
         [0040]    As shown in  FIG. 2 , the heat sink  12  comprises a central heat sink segment  14  and two edge heat sink segments  16   a ,  16   b  connected to the central heat sink segment  14 . These three segments are assembled together as will be described in detail with reference to  FIGS. 5 to 8 . This method is employed to changed the size of the heat sink by simply altering the middle section. 
         [0041]    The lighting apparatus incorporating the troffer assembly of embodiments of the present invention will likely be installed within a ceiling as a recessed down light. In this configuration, there may be requirements to insulate electrical circuitry of the LEDs from the interior of the ceiling. This requirement is met in the embodiment of  FIGS. 1 and 2  since the heat sink  12  substantially covers the hole within the back planar side of the container, thus separating any electrical circuitry within the troffer assembly from the interior of the ceiling. This requirement is met without needing to extend the frame  10  over the back planar side of the container, which may have limited the effectiveness of the heat sink  12 . In particular, the fins within the heat sink  12  would lose effectiveness if implemented within the interior of the container, due to limited airflow to perform passive cooling within the container. 
         [0042]    Although the troffer assembly of  FIGS. 1 and 2  has a single hole in the back planar side of the container, in other embodiments, the frame  10  may form the back planar side of the container and there may be a plurality of holes within the frame  10 . In this case, there may be a plurality of heat sinks, each heat sink having a planar dimension substantially similar to the dimension of a corresponding hole in the frame  10  within the back planar side of the container. 
         [0043]    In these embodiments, there remains physical separation between the electrical circuitry within the troffer assembly and the interior of the ceiling while still allowing the heat sinks have a planar side exterior to the container. 
         [0044]    In one specific implementation, for each light engine module implemented within the lighting apparatus of the present invention, there may be a corresponding hole in the back planar side of the frame  10  and a corresponding heat sink that covers the hole. In this implementation, each light engine module could be physically and thermally coupled to a separate heat sink. 
         [0045]    For example, in the case that there are four light engine modules implemented within a lighting apparatus according to an embodiment of the present invention, each light engine module being approximately the size of one quarter of the heat sink  12  in  FIG. 1 , the frame  10  may include two perpendicular elements that cross the back planar side of the container in order to divide the back planar side of the container into four equal squares. In this case, four heat sinks could be integrated within the back planar side of the container, each one being physically and thermally coupled to a separate light engine module. 
         [0046]    Although the planar sides of the troffer assembly of  FIGS. 1 and 2  are in the shape of a square, this should not limit the scope of the present invention. In particular, there are numerous planar shapes possible for a troffer assembly of the present invention. Specifically, the planar sides of the container formed with the frame  10  could be any two- dimensional shape including a rectangle, a triangle, another polygon or even a circle or oval. 
         [0047]      FIG. 2   a  is an alternative embodiment of the heat sink of  FIG. 2  wherein the extruded fins  13  are omitted. 
         [0048]      FIGS. 3 and 4  are top and bottom views respectively of a lighting apparatus comprising the troffer assembly of  FIGS. 1 and 2 . As shown, the lighting apparatus comprises the frame  10  and heat sink  12  of  FIGS. 1 and 2  and further comprise a planar optical element  18  connected to the frame  10  along the edge of the hole in the front planar side of the container. The optical element  18  may be connected to the frame  10  with an interlocking connection or alternatively another fastening mechanism (ex. screws, clips, snap connection, affixing agent etc.). The planar optical element  18  is used to diffuse light generated from light engine modules (not shown) within the troffer assembly. As shown in  FIG. 3 , the planar optical element  18  has planar dimensions substantially similar to dimensions of the hole in the front planar side of the frame  10  such that it covers the hole when installed. 
         [0049]      FIG. 3   a  is an exploded view of the heat sink assembly of  FIGS. 1-3 . As shown in  FIG. 3   a , a particularly novel and advantageous feature of the present invention is the provision of a thermal interface layer  15  between the heat sink  14  and a printed circuit board  17  of the assembly  10  onto which the LEDs (not shown) are mounted. In the illustrative embodiment, the thermal interface layer  17  includes a thin layer of carbon graphite to maximize thermal extraction. The thermal interface layer  17  provides heat extraction in excess of 600 W/m-K in the x-y plane (along the surface of the material) and good extraction through the material (in the z plane) as well. This offers a significant improvement over convention heat sinks that perform well in the extraction of heat in the z-direction and poor heat extraction along the x-y plane thereof. 
         [0050]    The lighting apparatus, as shown in  FIG. 4 , further comprises an AC/DC power supply module  20  and a lighting control module  22  connected to the second planar side of the heat sink  12 . In this case, the AC/DC power supply module  20  and the lighting control module comprise an AC/DC power supply and a lighting controller respectively encapsulated within respective rectangular encasements. The AC/DC power supply and the lighting controller are electrically coupled to each other and manage the DC power to the light engine modules within the lighting apparatus. Cables (not shown) connecting the lighting controller to the light engine modules can be wired through a hole  24  within the center of the heat sink  12  that is shown in  FIGS. 1 and 2 . As shown in  FIG. 4 , the hole  24  is covered by one of the power supply module  20  and/or the light control module  22 . 
         [0051]      FIGS. 5 through 8  are directed to components of the heat sink  12  and assembly of those components to manufacture the heat sink  12 .  FIG. 5  is a perspective view of the central heat sink segment  14  of the heat sink  12  illustrated within  FIG. 2 .  FIG. 5   a  is a magnified view of a portion of the heat sink segment depicted in  FIG. 5 . As shown, the central heat sink segment  14  comprises a plurality of fins  13  coupled to and substantially perpendicular to the second planar surface of the central heat sink segment  14 . On either edge perpendicular to the fins, the central heat sink segment  14  comprises a coupling mechanism  26 . (See  FIG. 5   a .) As shown, the coupling mechanism  26  comprises a female portion of an interlocking connection, though other mechanisms for coupling to other heat sink segments could be used. 
         [0052]      FIG. 6  is a perspective view of one of the edge heat sink segments  16   a  of the heat sink  12  illustrated within  FIG. 2 .  FIG. 6   a  is a magnified view of a portion of the second segment depicted in  FIG. 6 . As shown, similar to the central heat sink segment  14  of  FIG. 5 , the edge heat sink segment  16   a  comprises a plurality of fins  13  coupled to and substantially perpendicular to the second planar surface of the edge heat sink segment  16   a . On one edge perpendicular to the fins, the edge heat sink segment  16   a  comprises a coupling mechanism  28 . As shown, the coupling mechanism  28  comprises a male portion of an interlocking connection that could interlock with the female portion of the central heat sink portion of  FIG. 5 , though other mechanisms for coupling to other heat sink segments could be used. 
         [0053]      FIG. 7  is a perspective view of the heat sink  12  after the central heat sink segment  14  has been assembled with the two edge heat sink segments  16   a ,  16   b .  FIG. 7   a  is a magnified view of a portion of the heat sink depicted in  FIG. 7 . As shown, the coupling mechanism  26  of the central heat sink segment  14  and the coupling mechanism  28  of the edge heat sink segment  16   a  interlock together to form a connection  30 . A similar connection can be made between the central heat sink segment  14  and the edge heat sink segment  16   b . Further, in some embodiments, other coupling mechanisms may be used as well or in place of the coupling mechanism shown in  FIG. 7 . For example, to assemble the heat sink segments  14 ,  16   a ,  16   b  screws, clips, snap connection, affixing agent etc. may be used. 
         [0054]      FIG. 8  is a detailed schematic of the heat sink of  FIG. 7  which illustrates how the combination of the central heat sink segment  14  and the edge heat sink segments  16   a , 16   b  combine to form the square planar heat sink  12 . In embodiments of the present invention, one or more of the segments of the heat sink  12  may be reconfigured with other segments in order to generate other sizes and/or shapes of heat sinks for installation in troffer assemblies of different size and/or shape. One particular modified heat sink will be described with reference to  FIGS. 12 to 15 . 
         [0055]    Although the heat sink segments  14 , 16   a , 16   b  depicted in  FIGS. 5 to 8  have coupling mechanisms that are parallel with their fins, it should be understood that the coupling mechanisms could alternatively be perpendicular to the fins or, in the case that the fins are not parallel with any of the edges of the heat sink segments  14 , 16   a , 16   b , the coupling mechanisms may have no relationship to the direction of the fins. Further, in some embodiments of the present invention, the fins on the heat sink segments  14 , 16   a ,  16   b  could be replaced or supplemented with other implementations for increasing the surface area of the heat sink segments and/or other cooling techniques. 
         [0056]      FIGS. 9 ,  10  and  11  depict an alternative embodiment of the troffer assembly and lighting apparatus to that depicted in  FIGS. 1 to 4 . In particular, in the embodiment depicted in  FIGS. 9 ,  10  and  11 , the troffer assembly and lighting apparatus are significantly reduced in size. In some embodiments, the lighting apparatus of  FIGS. 3 and 4  is approximately 2 feet×2 feet while the lighting apparatus of  FIG. 11  is 1 foot by 1 foot. Other dimensions for the lighting apparatus of the present invention are possible and these are only sample dimensions. 
         [0057]      FIGS. 9 and 10  are top and bottom views respectively of a troffer assembly according to the embodiment of the present invention in which the dimensions are reduced. As shown, the troffer assembly comprises a frame  40  and a heat sink  42  similar to the frame  10  and heat sink  12  described above with reference to  FIGS. 1 and 2 . Similarly, the frame  40  has four sides that form an edge of a container with front and back square planar sides. The front and back planar sides of the container each have a hole that is substantially the size of the respective planar sides, hence leaving both planar sides open with the frame  40  only forming the outside edge of the container. The heat sink  42  is connected to the frame  40  at the back planar side of the container. Similar to the embodiment of  FIGS. 1 and 2 , the heat sink  42  has a planar dimension substantially similar to the dimension of the hole in the back planar side of the container. The heat sink  42  is connected to the frame  40  along the edge of the hole in the back planar side of the container such that the hole is fully covered. The heat sink  42  may be connected to the frame  40  with a series of screws or alternatively another fastening mechanism (ex. interlocking connection, clips, snap connection, affixing agent etc.). 
         [0058]    As shown in  FIGS. 9 and 10 , the heat sink  42  comprises first and second planar sides. The first planar side of the heat sink  42  is a flat surface and forms an interior side of the container. When the lighting apparatus according to embodiments of the present invention is assembled, one or more light engine modules (not shown) comprising LEDs are both physically and thermally coupled to the first planar side of the heat sink  42 . The second planar side of the heat sink  42  comprises a plurality of fins as shown in  FIG. 10  and forms an exterior side of the container. Similar to the heat sink  12 , the fins within the heat sink  42  may be implemented in many different manners and may be removed, replaced or supplemented with other cooling technologies. As shown in  FIG. 10 , the heat sink  42  comprises a central heat sink segment  44  and two edge heat sink segments  46   a ,  46   b  connected to the central heat sink segment  44 . These three segments are assembled together as will be described in detail with reference to  FIGS. 12 to 15 . 
         [0059]      FIG. 11  is a side view of a lighting apparatus comprising the troffer assembly of  FIGS. 9 and 10 . As shown, the lighting apparatus comprises the frame  40  and heat sink  42  of  FIGS. 9 and 10  and further comprises a planar optical element  48  connected to the frame  40  along the edge of the hole in the front planar side of the container. The optical element  48  may be connected to the frame  40  with an interlocking connection or alternatively another fastening mechanism (ex. screws, clips, snap connection, affixing agent etc.). The planar optical element  18  is used to diffuse light generated from light engine modules (not shown) within the troffer assembly. As shown in  FIG. 11 , the planar optical element  48  has planar dimensions substantially similar to dimensions of the hole in the front planar side of the frame  40  such that it covers the hole when installed. 
         [0060]    Although not shown, the lighting apparatus of  FIG. 11  would also comprise an AC/DC supply voltage module and a light control module similar to that depicted above in  FIG. 4 . Further, similar to the hole  24  within the heat sink  12 , the heat sink  42  has a hole  50  that can be used for cabling and can be covered by other components such as an AC/DC power supply module and/or a light control module. 
         [0061]      FIGS. 12 through 15  are directed to components of the heat sink  42  and assembly of those components to manufacture the heat sink  42 . In this case, the segments  44 ,  46   a ,  46   b  of the heat sink  42  are similar to those described above for the heat sink  12 . The difference is the dimensions of the heat sink  42  relative to the heat sink  12 , and therefore the dimensions of the heat sink segments  44 ,  46   a ,  46   b.    
         [0062]    In the embodiments of the present invention depicted in  FIGS. 12 to 15 , the edge heat sink segments  46   a ,  46   b  are substantially the same as the edge heat sink segments  16   a , 16   b  but with the length of the segments reduced. In this case, the reduction in size of the heat sink  42  relative to the heat sink  12  is primarily due to a change in size of the central heat sink segment  44 . By using edge heat sink segments  46   a ,  46   b  in the 1×1 troffer assembly of  FIGS. 9 and 10  that are substantially the same width and structure as the edge heat sink segments  16   a , 16   b  used in the 2×2 troffer assembly of  FIGS. 1 and 2 , a reduction in SKUs can be used in the manufacturing process of the heat sinks. In particular, a single SKU of edge heat sink segments can be generated for manufacturing of both the 1×1 and 2×2 troffer assemblies. By simply reducing the length of the edge heat sink assemblies  16   a , 16   b , edge heat sink assemblies  46   a , 46   b  can be created. 
         [0063]      FIGS. 12 and 13  are perspective views of the central heat sink segment  44  and the edge heat sink segment  46   a  respectively.  FIGS. 12   a  and  13   a  are magnified views of portions of the segments depicted in  FIGS. 12 and 13  respectively. As shown in  FIG. 12 , the central heat sink segment  44  comprises a relatively narrow longitudinal heat sink element that in this case only comprises a single fin. In other implementations, the central heat sink segment  44  may comprise more than one fin or no fins whatsoever. This central heat sink segment  44  comprises a coupling mechanism on each longitudinal edge similar to the coupling mechanism  26  of  FIG. 5 . Similarly, the coupling mechanism could be replaced and/or supplemented with alternative mechanisms for coupling the central heat sink segment  44  to the edge heat sink segments  46   a , 46   b . As shown in  FIG. 13 , the edge heat sink segment  44   a  comprises a coupling mechanism  54  similar to that of coupling mechanism  28  of  FIG. 6 . 
         [0064]      FIG. 14  depicts the elements of achieving interlocking of the heat sinks.  FIG. 14  is a perspective view of the heat sink  42  after the central heat sink segment  44  has been assembled with the two edge heat sink segments  46   a ,  46   b .  FIG. 14   a  is a magnified view of a portion of the assembled heat depicted in  FIG. 14 . As shown, the coupling mechanism  46  of the central heat sink segment  44  and the coupling mechanism  48  of the edge heat sink segment  46   a  interlock together to form a connection  40 . A similar connection can be made between the central heat sink segment  44  and the edge heat sink segment  46   b . Further, in some embodiments, other coupling mechanisms may be used as well or in place of the coupling mechanism shown in  FIG. 14 . For example, to assemble the heat sink segments  44 , 46   a , 46   b  screws, clips, snap connection, affixing agent etc. may be used. 
         [0065]      FIG. 15  is a detailed schematic of the heat sink of  FIG. 14  which illustrates how the combination of the central heat sink segment  44  and the edge heat sink segments  46   a , 46   b  combine to form the square planar heat sink  42 . As shown and described above, the edge heat sink segments  46   a , 46   b  are similar in dimensions to the edge heat sink segments  16   a , 16   b  of  FIG. 8  but with their lengths reduced. Their widths remain in both cases the same. 
         [0066]    In alternative embodiments of the present invention, instead of changing the dimensions of the central heat sink segment, the edge heat sink segments could be adjusted. In one example implementation, the width of the edge heat sink segments could be reduced substantially while the width of the central heat sink segment would remain constant when reducing the size of the troffer assembly. In this case, the length of the central heat sink segment would need to be reduced but the width could remain constant. 
         [0067]      FIG. 16  shows an alternative embodiment in which the troffer assembly  100  includes four modules  102 ,  104 ,  106  and  108  instead of one. Each module is complete and independent allowing for economic and efficient of any one module without replacing the others. 
         [0068]      FIG. 17  is a perspective view showing the completed lighting assembly. 
         [0069]    Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof. 
         [0070]    It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention. 
         [0071]    Accordingly,