Patent Publication Number: US-9423117-B2

Title: LED fixture with heat pipe

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a light emitting device assembly that can provide lighting and is well-suited for use with solid state lighting sources, such as light emitting diodes (LEDs). 
     2. Description of the Related Art 
     Lighting fixtures are ubiquitous in commercial offices, industrial and residential spaces throughout the world. In many instances the lighting fixtures, for example troffer fixtures, are mounted to or suspended from ceilings, or even recessed into the ceiling and house elongated fluorescent light bulbs that span the length of the troffer. In instances when the troffer is recessed into the ceiling, the back side of the troffer protrudes into the plenum area above the ceiling. Elements of the troffer fixture can be included on the back side to dissipate heat generated by the light source into the plenum where air can be circulated to facilitate the cooling mechanism. 
     More recently, with the advent of the efficient solid state lighting sources, LEDs have been used as the source for indirect lighting, for example. LEDs are solid state devices that convert electric energy to light and generally comprise one or more active regions of semiconductor material interposed between oppositely doped semiconductor layers. When a bias is applied across the doped layers, holes and electrons are injected into the active region where they recombine to generate light. Light is produced in the active region and emitted from surfaces of the LED. 
     LEDs have certain characteristics that make them desirable for many lighting applications that were previously the realm of incandescent or fluorescent lights. Incandescent lights are very energy-inefficient light sources with a vast majority of the electricity they consume being released as heat rather than light. Fluorescent light bulbs are more energy efficient than incandescent light bulbs, but are still relatively inefficient. LEDs by contrast, can emit the same luminous flux as incandescent and fluorescent lights using a fraction of the energy. 
     In addition, LEDs can have a significantly longer operational lifetime. Incandescent light bulbs have relatively short lifetimes, with some having a lifetime in the range of about 750-1000 hours. Fluorescent bulbs can also have lifetimes longer than incandescent bulbs such as in the range of approximately 10,000-20,000 hours, but provide less desirable color reproduction. In comparison, LEDs can have lifetimes between 50,000 and 70,000 hours. The increased efficiency and extended lifetime of LEDs is attractive to many lighting suppliers and has resulted in LED lights being used in place of conventional lighting in many different applications. It is predicted that further improvements will result in their general acceptance in more and more lighting applications. An increase in the adoption of LEDs in place of incandescent or fluorescent lighting would result in increased lighting efficiency and significant energy saving. 
     Some recent designs have incorporated an indirect lighting scheme in which the LEDs or other sources are aimed in a direction other than the intended emission direction. This may be done to encourage the light to interact with internal elements, such as diffusers, for example. One example of an indirect fixture can be found in U.S. Pat. No. 7,722,220 to Van de Ven which is commonly assigned with the present application. 
     Modern lighting applications often demand high power LEDs for increased brightness. High power LEDs can draw large currents, generating significant amounts of heat that must be managed. Many systems utilize heat sinks which must be in good thermal contact with the heat-generating light sources. Troffer-style fixtures generally dissipate heat from the back side of the fixture that extends into the plenum. This can present challenges as plenum space decreases in modern structures. Furthermore, the temperature in the plenum area is often several degrees warmer than the room environment below the ceiling, making it more difficult for the heat to escape into the plenum ambient. 
     SUMMARY 
     The invention provides various embodiments of light emitting device assemblies that are efficient, reliable and cost effective and can be arranged to provide a direct or indirect lighting scheme. The different embodiments comprise elements to displace the light source remote from the housing, such that the displacing elements are thermally conductive to conduct heat from the light source to the housing. The displacing elements can comprise many different materials or devices arranged in different ways, with some assemblies comprising heat pipe displacing elements coupled to one or more heat spreaders. 
     In one embodiment, as broadly described herein, a lighting assembly comprises a housing including a front surface, a light emitting device on a first heat spreader remote from the front surface, a first end of a heat pipe in thermal communication with the first heat spreader and the heat pipe extending towards the front surface such that a second end of the heat pipe is in thermal communication with a second heat spreader that is disposed on an external surface of the housing. The first heat spreader, heat pipe and second heat spreader forming a thermally conductive path to conduct heat away from the first end of the heat pipe towards the second end of the heat pipe. A reflector is proximate to the light emitting device, the reflector comprising a reflective surface facing the housing. A diffuser can also be included to diffuse light emitting from the light emitting device into the desired emission pattern. 
     In another embodiment, a lighting assembly comprises a housing comprising a back surface and angled sidewalls, a plurality of heat spreaders wherein a first heat spreader has a mount surface and a light emitting device mounted on the mount surface and at least one second heat spreader on an external surface of the housing. Each of the one or more heat pipes in thermal communication with the first heat spreader and the at least one second heat spreader. The back surface of the housing can be planar, curved, multi-faceted or a combination thereof. In some embodiments, the at least one second heat spreader can be on an external surface of the angled sidewalls of the housing, the back surface of the housing, or a combination thereof. The first heat spreader, heat pipe and the at least one second heat spreader forming a thermally conductive path to conduct heat away from the light emitting device. 
     These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings which illustrate by way of example the features of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a lighting assembly according to an embodiment of the invention. 
         FIG. 2A  is a cross-sectional view of the lighting assembly of  FIG. 1 . 
         FIG. 2B  is an overhead view of the lighting assembly of  FIG. 2 . 
         FIG. 3A  is a cross-sectional view of a lighting assembly according to an embodiment of the invention. 
         FIG. 3B  is a cross-sectional view of a lighting assembly according to an embodiment of the invention. 
         FIG. 3C  is a perspective view of a lighting assembly according to an embodiment of the invention. 
         FIG. 4  is a perspective view of a lighting assembly according to an embodiment of the invention. 
         FIG. 5  is a cross-sectional view of the lighting assembly of  FIG. 4 . 
         FIG. 6  is a cross-sectional view of a lighting assembly according to an embodiment of the invention. 
         FIG. 7  is a cross-sectional view of a lighting assembly according to an embodiment of the invention. 
         FIG. 8  is a cross-sectional view of a lighting assembly according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention described herein is directed to different embodiments of light emitting device assemblies that in some embodiments provide displacing elements to mount a light source remote from a housing of the assembly. The displacing elements can comprise many different thermally conductive materials, as well as multiple material devices arranged to conduct heat. In some embodiments, the elements can comprise a first heat spreader including a mounting surface to mount one or more LEDs, and one or more heat pipes, wherein the LEDs are arranged to emit substantially all light towards the housing where it can be mixed and/or shaped before it is emitted from the housing as useful light. One end of the heat pipe is in thermal contact with the first heat spreader and the other end of the heat pipe can be mounted to a second heat spreader that is on an external surface of the housing, such that the orientation of the one or more heat pipes displaces the LEDs from the housing. The heat pipes also conduct heat from the LEDs to the second heat spreader where the heat can efficiently radiate into the ambient. In some embodiments the housing is made of thermally conductive materials such that the housing further assists in the dissipation of heat. This arrangement allows for the LEDs to operate at a lower temperature, while allowing the LEDs to remain remote from the housing. In addition, a thermally conductive housing could eliminate the need of an active cooling system, thereby reducing manufacturing costs. However, in other embodiments, an active cooling system could be present to assist in the heat dissipation. The thermally conductive housing would allow for the LEDs to be driven with a higher drive signal to produce a higher luminous flux. Operating at lower temperatures can provide the additional advantage of improving the LED emission and increase the lifespan of the assembly. 
     Heat pipes are generally known in the art and are only briefly discussed herein. Heat pipes can comprise a heat-transfer device that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two interfaces. At the hot interface (i.e. interface with LEDs) within a heat pipe, a liquid in contact with a thermally conductive solid surface turns into a vapor by absorbing heat from that surface. The vapor condenses back into a liquid at the cold interface, releasing the latent heat. The liquid then returns to the hot interface through either capillary action or gravity action where it evaporates once more and repeats the cycle. In addition, the internal pressure of the heat pipe can be set or adjusted to facilitate the phase change depending on the demands of the working conditions of the thermally managed system. 
     A typical heat pipe is comprised of a sealed pipe or tube made of a material with high thermal conductivity, such as copper or aluminum at least at both the hot and cold ends. A vacuum pump can be used to remove air from the empty heat pipe, and the pipe can then be filled with a volume of working fluid (or coolant) chosen to match the operating temperature. Examples of such fluids include water, ethanol, acetone, sodium, or mercury. Due to the partial vacuum that can be near or below the vapor pressure of the fluid, some of the fluid can be in the liquid phase and some will be in the gas phase. 
     Displacing the LEDs on the first heat spreader remote from the housing can provide a number of additional advantages beyond those mentioned above. Mounting the LEDs on the first heat spreader remote from the housing allows for a concentrated LED light source that more closely resembles a point source. The LEDs can be mounted close to one another on the first heat spreader with very little separation between adjacent LEDs. This can result in a light source where the individual LEDs are less visible and can provide overall lamp emission with enhanced color mixing. Additionally, the heat pipe could be configured vertically or at an upward vertical angle such that the LEDs are below the housing and this configuration would allow gravity to assist in the operation of the heat pipe. The LEDs being below the housing and arranged to emit substantially all light towards the housing allows for the housing to be used to shape and/or mix the light before it is emitted from the housing as useful light. As such, a lens could be eliminated thereby providing a lens-free construction which further reduces manufacturing costs. However, in some embodiments, a lens could be included. 
     Different embodiments of the invention can incorporate diffuser domes wherein the LEDs are on the first heat spreader within the diffuser dome. In this arrangement, the LEDs are arranged to emit substantially all light downward such that the assembly is a down-light source. A second heat spreader is mounted to a ceiling and the heat pipe extends from the first heat spreader to the second heat spreader to form the thermal conductive path. The diffuser not only serves the purpose of concealing the internal components of the assembly from the view of a user, but can also mix and/or shape the light into a desired emission pattern. In other embodiments, the second heat spreader can be mounted to the external surface of the diffuser, instead of being mounted to a ceiling, and a mounting bracket is mounted to the ceiling wherein a cord or the like is connected to the mounting bracket and the diffuser so as to suspend the diffuser and LED from the ceiling. This arrangement allows for a shorter length of the heat pipe to be used and allows the length that the diffuser and LED are suspended from the ceiling to be easily adjusted without interfering with the heat dissipating elements. 
     The invention is described herein with reference to certain embodiments, but it is understood that the invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In particular, the present invention is described below in regards to certain lighting components having LEDs, LED chips or LED components in different configurations, but it is understood that the invention can be used for many other lamps having many different configurations. The components can have different shapes and sizes beyond those shown and different numbers of LEDs or LED chips can be included. Many different commercially available LEDs can be used such as those commercially available from Cree, Inc. These can include, but not limited to Cree&#39;s XLamp® XP-E LEDs or XLamp® XP-G LEDs. 
     It is to be understood that when an element or component is referred to as being “on” another element or component, it can be directly on the other element or intervening elements may also be present. Furthermore, relative terms such as “between”, “within”, “adjacent”, “below”, “proximate” and similar terms, may be used herein to describe a relationship of one element or component to another. It is understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. 
     Although the terms first, second, etc. may be used herein to describe various elements or components, these elements or components should not be limited by these terms. These terms are only used to distinguish one element or component from another. Thus, a first element discussed herein could be termed a second element without departing from the teachings of the present application. It is understood that actual systems or fixtures embodying the invention can be arranged in many different ways with many more features and elements beyond what is shown in the figures. 
     As used herein, the term “source” can be used to indicate a single light emitter or more than one light emitter functioning as a single source. For example, the term may be used to describe a single blue LED, a blue-shifted-yellow (BSY) LED, or it may be used to describe a red LED and a green LED in proximity emitting as a single source. Thus, the term “source” should not be construed as a limitation indicating either a single-element or a multi-element configuration unless clearly stated otherwise. 
     Embodiments of the invention are described herein with reference to cross-sectional view illustrations that are schematic illustrations. As such, the actual thickness of elements can be different, and variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances are expected. Thus, the elements illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the invention. 
     With reference to  FIGS. 1 and 2A , an exemplary lighting assembly  10  is shown. In some embodiments the lighting assembly  10  is configured such that the assembly  10  can be recessed into a wall or ceiling and used in conjunction with a power supply. The assembly  10  comprises a housing  20  including a front surface  21  on one side and a back surface  23  opposite the front surface  21 . A light emitting device  12 , for example an LED, is mounted on a first heat spreader  14 , such that the light emitting device on the first heat spreader  14  is remote from the front surface  21  of the housing  20 . 
     To facilitate the dissipation of unwanted thermal energy away from the light emitting device  12 , a heat pipe  16  is disposed proximate to the first heat spreader  14 . A first end  17  of the heat pipe  16  is coupled to the first heat spreader  14  and the heat pipe  16  extends towards the front surface  21  of the housing  20 . The first heat spreader  14 , which is exposed to the ambient room environment, comprises an opening to receive the first end  17  of the heat pipe  16 . A second heat spreader  18  is disposed on the back surface  23  of the housing  20  and a second end  19  of the heat pipe  16  is coupled to the second heat spreader  18 . The second heat spreader  18  has an opening to receive the second end  19  of the heat pipe  16 . The length of the heat pipe  16  determines the separation distance between the light emitting device  12  and the housing  20 . The length of the heat pipe  16  is selected to properly displace the light source remote from the front surface  21  to provide an efficient thermal path, in accordance with a desired lighting output. The heat pipe  16  is also adapted to provide structural support for the first heat spreader  14 . 
     The portion of the first heat spreader  14  that faces the front surface  21  of the housing  20  functions as a mount surface  13  for the light emitting device  12 . One or more light emitting devices  12  can be disposed on the mount surface  13  of the first heat spreader  14 . In operation, substantially all light emitted from the light emitting devices  12  is directed towards the housing  20  where it can be mixed and/or shaped before it is emitted from the housing  20  as useful light. Emitting the light to the housing  20  allows the assembly  10  to operate as an indirect light source. The first heat spreader  14  can also comprise a reflector  22  adjacent the light emitting device  12  to direct substantially all light towards the front surface  21 . In another embodiment, the assembly  10  comprises a lens that encases the light emitting device  12 . The lens can comprise light altering properties similar to the housing  20 . In yet other embodiments, the first heat spreader  14  can be configured to have a region  25  opposite the mount surface  13  that assists in the emission of a uniform light, such that the emitted light does not have an unpleasant glare or hot spots. For example, the region  25  could be a darkened region that can soften the emitted light in instances of high concentration of light is directly underneath the assembly. 
     The housing  20  further comprises sidewalls  28  adjacent the front surface  21  and are configured such that the sidewalls  28  may be angled, curved, multi-faceted or a combination thereof to assist in shaping and/or mixing the light. The sidewalls  28  and the front surface  21  may comprise many different materials. For many indoor lighting applications, it is desirable to present a uniform, soft light source without unpleasant glare, color stripping, or hot spots. Thus, the sidewalls  28  and front surface  21  may comprise a diffuse white reflector such as a microcellular polyethylene terephthalate (MCPET) material or a Dupont/WhiteOptics material, for example. Other white diffuse reflective materials can also be used, such as but not limited to reflective paint. The housing  20  can be formed of metal, steel, aluminum, any other material that is thermally conductive or a combination thereof. However, in other embodiments the housing  20  can be formed of non-thermally conductive materials. The housing  20  may be in the form of many different shapes. For example, in one embodiment, the front surface  21  is planar with sidewalls  28  adjacent the front surface  21 . In other embodiments, the front surface  21  of the housing is a curved surface with the sidewalls  28  adjacent the curved surface. 
     Diffuse reflective coatings have the inherent capability to mix light from solid state light sources having different spectra (i.e., different colors). These coatings are particularly well-suited for multi-source designs where two different spectra are mixed to produce a desired output color point. For example, LEDs emitting blue light may be used in combination with other sources of light, e.g., yellow light to yield a white light output. In some embodiments, the sidewalls  28  and front surface  21  may be coated with a phosphor material that converts the wavelength of at least some of the light from the light emitting diodes to achieve a light output of the desired color point when the assembly  10  is in operation. 
     By using a diffuse white reflective material for the sidewalls  28  and front surface  21  and by positioning the light emitting device  12  to emit light first toward the sidewalls  28  and front surface  21  several design goals are achieved. For example, the sidewalls  28  and front surface  21  perform a color-mixing function, effectively doubling the mixing distance and greatly increasing the surface area of the light emitting device. Additionally, the surface luminance is modified from a bright, uncomfortable point source to a much larger, softer diffuse reflection. A diffuse white material also provides a uniform luminous appearance in the output. 
     The sidewalls  28  and front surface  21  can comprise materials other than diffuse reflectors. In other embodiments, the sidewalls  28  and front surface  21  can comprise a specular reflective material or a material that is partially diffuse reflective and partially specular reflective. In some embodiments, it may be desirable to use a specular material in one area and a diffuse material in another area. 
     The heat pipe  16  is a typical heat pipe known in the art and is only discussed briefly herein. Heat pipes have tremendously higher thermal conductivity than copper or aluminum and can move significant heat from a concentrated light source. The first and second heat spreaders  14 ,  18  at either end of the heat pipe  16  aid in efficient heat dissipation. Heat pipe  16  can also be covered with Dupont/WhiteOptics material, similar to the front surface  21  and sidewalls  28  so as to not block emitted light, affect color mixing or otherwise negatively affect light emission during operation. Additionally, electrical wires from a power supply to provide power to the light emitting device  12  may run alongside the heat pipe  16  and also be covered by the Dupont/WhiteOptics material. However, the heat pipe and electrical wires may be covered with other material, similar to the front surface  21  and sidewalls  28  as discussed above. An advantage of the heat pipe  16  is that the length of the heat pipe between the first and second heat spreaders  14 ,  18  can be minimized to efficiently dissipate heat from the light emitting device  12  and the housing  20 . 
     A thermally conductive adhesive can be used to mount second heat spreader  18  onto the back surface  23 . However, a non-thermally conductive adhesive can also be used. In other embodiments the second heat spreader  18  can be mounted to the housing  20  using a screw, a bolt, rivet or the like. The second heat spreader  18  on the back surface  23  allows the housing  20  to be used to further dissipate heat from the light emitting device when in use. An advantage of utilizing the thermally conductive properties of the housing  20  to dissipate heat eliminates the need for a dedicated heat sink to dissipate heat. As such, the overall height of the lighting assembly  10  is decreased, which also reduces manufacturing costs. 
     The first and second heat spreaders  14 ,  18  can be constructed using many different thermally conductive materials. For example, the first and second heat spreaders  14 ,  18  may comprise an aluminum body. The first and second heat spreaders  14 ,  18  can also be extruded for efficient, cost-effective production and convenient scalability. 
     The first heat spreader  14  provides a substantially flat area on which one or more light emitting devices can be mounted. Although LEDs are used as the light emitting devices in various embodiments described herein, it is understood that other light sources, such as laser diodes for example, may be substituted in as the light sources in other embodiments of the invention.  FIG. 2B  shows an overhead view of the assembly of  FIG. 2A . In the embodiment of  FIG. 2B , the first and second heat spreaders and  18  are disc-shaped with an opening along a central vertical axis to receive the heat pipe  16 . However, the first heat spreader  14  is not limited to disk-shaped configurations, and may be in the form of any shape, such as but not limited to rectangle, triangle or any other polygon. 
     The housing  20 , in  FIGS. 2A &amp; 2B , is similar to an individual recessed light can. However, in other embodiments, the housing  20  can come in different shapes and sizes, for example a 2′×4′ troffer or a wall sconce. In yet other embodiments, the housing  20  can accommodate more than one heat pipe/heat spreaders configurations. In embodiments where the housing  20  is a troffer-style light fixture, the housing  20  can comprise a single light emitting device  12  and heat pipe  16  or a plurality of light emitting devices  12  and a plurality of corresponding heat pipes  16 . The troffer housing may be mounted to or suspended from a ceiling. In other embodiments, the troffer housing may be recessed into the ceiling, with the back side of the troffer protruding into the plenum area above the ceiling. 
     Many industrial, commercial, and residential applications call for white light sources. The assembly  10  may comprise one or more emitters producing the same color of light or different colors of light. In one embodiment, a multicolor source is used to produce white light. Several colored light combinations will yield white light. For example, it is known in the art to combine light from a blue LED with wavelength-converted yellow (blue-shifted-yellow) light to yield white light with correlated color temperature (CCT) in the range between 5000K to 7000K (often designated as “cool white”). Both blue and BSY light can be generated with a blue emitter by surrounding the emitter with phosphors that are optically responsive to the blue light. When excited, the phosphors emit yellow light which then combines with the blue light to make white. In this scheme, because the blue light is emitted in a narrow spectral range it is called saturated light. The BSY light is emitted in a much broader spectral range and, thus, is called unsaturated light. 
     Another example of generating white light with a multicolor source is combining the light from green and red LEDs. RGB schemes may also be used to generate various colors of light. In some applications, an amber emitter is added for an RGBA combination. The previous combinations are exemplary; it is understood that many different color combinations may be used in embodiments of the present invention. Several of these possible color combinations are discussed in detail in U.S. Pat. No. 7,213,940 to Van de Ven et al., herein incorporated by reference. 
     In the embodiment of the assembly  10 , in  FIGS. 1, 2A and 2B , the first heat spreader  14  is exposed to the ambient environment. This structure is advantageous for several reasons. For example, air temperature in a typical residential or commercial room is much cooler than the air above the fixture (or the ceiling if the fixture is mounted above the ceiling plane). The air beneath the fixture is cooler because the room environment must be comfortable for occupants; whereas in the space above the fixture, cooler air temperatures are much less important. Additionally, room air is normally circulated, either by occupants moving through the room or by heating, ventilation, and air conditioning (HVAC) systems. The movement of air throughout the room helps to break the boundary layer, facilitating thermal dissipation from the first heat spreader  14 . 
       FIG. 3A  discloses an assembly  30  that is another embodiment of the invention. For the same or similar elements or features, the reference numbers from  FIGS. 1 and 2A /B, will be used throughout the application herein. The assembly  30  comprises one or more heat pipes  16  coupled to the first heat spreader  14 . In the embodiment of  FIGS. 1, 2A and 2B , the heat pipe  16  is coupled to the first heat spreader  14  at a central vertical axis. However, in the embodiment disclosed in  FIG. 3 , the one or more heat pipes  16  are coupled to the first heat spreader  14  at a side surface  15  of the first heat spreader  14 . The one or more heat pipes  16  extend towards the sidewalls  28 , instead of the front surface  21 . A corresponding one or more second heat spreaders  18  are disposed on an external surface  29  of the sidewalls  28  of the housing  20  and are configured to receive a respective heat pipe  16 . In this embodiment, the heat pipes  16  extend towards the housing  20  at an angle which thereby allows the front surface  21  of the housing  20  to be unobstructed, such that the heat pipes  16  do not block light emitted from the light emitting device when in operation. In other embodiments, the heat pipes  16  can be configured to be coupled to the first heat spreader  14  at the mount surface  13  where the light emitting device  12  is mounted, instead of the side surface  15 . In yet other embodiments, the heat pipes  16  are coupled to an edge  11 , formed by the intersection of the mount surface  13  and the side surface  15 , and extend towards the front surface  21  or the sidewalls  28  of housing  20 . In yet other embodiments, as shown in  FIG. 3C , the heat pipes  16  may be curved or angled such that when coupled to the first heat spreader  14 , the heat pipes  16  are substantially perpendicular to the side surface  15  of the first heat spreader  14  and extend towards the sidewalls  28 . These embodiments are but a few of the many different embodiments of the invention, and are not intended to limit the scope of the invention. 
       FIG. 3B  discloses an embodiment of an assembly  35  according to the invention. The assembly  35  is similar to assembly  30  in that the heat pipes  16  can be mounted on a side surface  15 , mount surface  13 , or edge  11  of the first heat spreader  14 . However, assembly  35  further discloses that the housing  20  has a curved front surface  21  with angled sidewalls  28  adjacent the curved front surface  21 . An advantage of the housing  20  of  FIG. 3B  is that the curved front surface  21  can reflect the emitted light so it can be uniformly emitted. The light emitting device  12  can be positioned at the focal point of the curved front surface  21  to ensure that substantially all light emitted from the light emitting device  12  is reflected and emitted as uniform light. Additionally, the assembly  35  can have one or more heat pipes  16 . For example, in one embodiment, a heat pipe  16  can be connected to the side surface  15  and extending to the housing  20 . In yet another embodiment, the assembly  35  can have a heat pipe  16  connected to the mount surface  13  of the first heat spreader  14  and another heat pipe  16  connected to the side surface  15  of the first heat spreader. In a further embodiment, the assembly  35  can have three heat pipes  16  as shown in  FIG. 3B . Again, these embodiments are but a few of the many different configurations, and are not intended to limit the scope of the invention. 
       FIGS. 4 and 5  show an embodiment of an assembly  40  according to the invention. The assembly  40  comprises a housing including a planar surface  41  that faces a light emitting device  12 . Assembly  40  is configured to be mounted onto a wall or ceiling and does not necessarily extend into the plenum area above the ceiling. However, in some embodiments the assembly  40  is configured to extend into the plenum area above the ceiling. Assembly  40  comprises a light emitting device  12 , first and second heat spreaders  14 ,  18  and a heat pipe  16 . Assembly  40  is further configured to comprise at least one connector  46  on a base  45  of housing  44  such that a dome-type lens  50  may be attached to assembly  40 . The dome-type lens  50  may be a decorative lens that covers the light emitting device  12 , or could be configured to perform a light altering effect to the light emitted, such as but not limited to wavelength conversion, dispersion, scattering and/or light shaping. 
     In another embodiment, the heat pipe  16  of  FIG. 5  could be configured such that it comprises an extension  43  that extends beyond the first heat spreader  14  and comprise an attachment means  48  to attach the dome-type lens  50  to the assembly  40 . For example, the extension  43  could comprise a threading or the like that extends beyond the dome-type lens  50  and adapted to receive a locking nut or the like to secure the dome-type lens  50  to the assembly  40 . In some embodiments, the extension  43  also provides a thermal path to dissipate heat from the light emitting device  12 , during operation, through the threading and through the housing  44  via the second heat spreader  18 , whereas in other embodiments, the extension  43  does not necessarily provide a thermal path to dissipate heat when the assembly is in use. The extension  43  could be formed of a heat pipe, thermally conductive material, or non-thermally conductive material. The extension  43  further provides structural support for the dome-type lens  50  such that at least one connector  46  is not needed. However, in other embodiments the at least one connector  46  and extension  43  are both present to provide structural support for the dome-type lens  50 . In yet another embodiment, the extension  43  may further comprise a control mechanism that is adapted to power-on or power-off the assembly, for example a pull-chain. 
       FIG. 6  shows an embodiment of an assembly  60  according to the invention. The assembly  60  comprises a light emitting device  12  on a first heat spreader  14 , a heat pipe  16  coupled to the first heat spreader  14  wherein the heat pipe  16  extends towards and couples to a second heat spreader  62 . The second heat spreader  62  is adapted to be mounted to a ceiling such that the light emitting device  12  is suspended from the ceiling. The assembly  60  further comprises a housing  64  remote from the second heat spreader and configured to enclose the light emitting device  12 . The housing  64  is further adapted to provide indirect lighting as disclosed above and can also comprise light mixing and/or light shaping properties as disclosed above. The housing  64  can be made of different materials, such as but not limited to plastic, glass, metal or a combination thereof. At least one advantage of the assembly  60  is that the heat pipe  16  allows the housing  64  to have an architectural design without having a heat sink restricting the architectural design of the housing  64 , whereas existing light assembly housing designs are constrained due to heat sink requirements, such as having a heat sink integrated into the housing in order to dissipate heat. The assembly  60  provides an efficient thermal path between the first heat spreader  14  and the second heat spreader  62  and to provide a desired lighting output. The heat pipe  16  is also adapted to provide structural support for the first heat spreader  14 . 
     In other embodiments, the assembly  60  can be configured to be a down-light source to provide direct lighting, instead of an indirect light source. In the direct light source embodiments, the light emitting device  12  is on an opposite surface of the first heat spreader  14  such that the light from the light emitting device is emitted downward. The housing  64  not only has diffusing properties to mix and/or shape the light into a desired emission pattern, but the housing  64  also serves the purpose of concealing the internal components of the assembly  60  from view. 
       FIG. 7  shows an embodiment of an assembly  70  according to the invention. The assembly  70  comprises a light emitting device  12  on a first heat spreader  14 , a heat pipe  16  coupled to the first heat spreader  14  wherein the heat pipe  16  extends towards and couples to a second heat spreader  72 . The assembly  70  further comprises an extension  74  that is coupled to the heat pipe  16  at one end and coupled to a base  76  at another end such that the light emitting device  12  is suspended from a ceiling. The base  76  is configured to be mounted to a ceiling and provide structural support for the assembly  70 . The second heat spreader  72  is adapted to be on an outer surface of a housing  78  and efficiently dissipate heat from the light emitting device  12 . The housing  78  is remote from the base  76  and configured to enclose the light emitting device  12 . The housing  78  is further adapted to be an indirect light source or a direct light source similar to assembly  60  and can also comprise light mixing and/or light shaping properties as disclosed above. The housing  78  can be made of different materials that are thermally conductive such that the housing also assists in dissipating heat from the light emitting device  12 . However, in other embodiments the housing  78  can be made of non-thermally conductive materials. At least one advantage of the assembly  70  is that the housing  78  allows for the light emitting device  12  to be remotely positioned within the housing  78  to provide a desired light output. The assembly  70  provides a thermal path between the first heat spreader  14  and the second heat spreader  72  while minimizing the length of the heat pipe  16 . In some embodiments the extension  74  can be made of thermally conductive materials to further assist in the heat dissipation. In yet other embodiments, the extension  74  can be made of non-thermally conductive material. At least one advantage of the assembly  70  is that the length that the housing  78  is suspended from the ceiling does not require the lengthening of the heat pipe  16 . The extension  74  can be modified to alter the height that the housing  78  is suspended from the ceiling. 
       FIG. 8  shows an embodiment of an assembly  80  according to the invention. The assembly  80  comprises a light emitting device  12  on a first heat spreader  14 , a heat pipe  82  coupled to the first heat spreader  14  wherein the heat pipe  82  extends towards and couples to a second heat spreader  89 . The second heat spreader  89  is adapted to be mounted to a ceiling such that the light emitting device  12  is suspended from the ceiling. In some embodiments, the second heat spreader  89  can be mounted above the ceiling or within the ceiling. In yet other embodiments, the second heat spreader  89  can be embedded within or mounted onto a ceiling tile or similar structure, wherein the ceiling tile is a typical ceiling tile used in commercial or residential settings and/or is formed of thermally conductive materials to assist in the heat dissipation. The heat pipe  82  can be comprised of a plurality of portions or could be an individual heat pipe. In one embodiment, the heat pipe  82  comprises a first portion  84 , a second portion  86  and a third portion  88 , wherein the first portion  84  is coupled to the first heat spreader  14 , the third portion  88  is coupled to the second heat spreader  89 , and the second portion is coupled to both the first portion  84  and the third portion  88 . The first and third portions  84 ,  88  can be formed of a copper heat pipe or other metallic heat pipe, whereas the second portion  86  can be a non-metallic low cost heat pipe or a heat conduit. In yet other embodiments the second portion  86  is further adapted to be flexible to allow the light emitting device  12  to be manipulated to provide a desired light output. At least one advantage of the assembly  60  is that the heat pipe  82  minimizes the length of the first and third portions  84 ,  88  of the heat pipe  82  while still providing an efficient thermal path between the first heat spreader  14  and the second heat spreader  89 . Yet another advantage of the assembly  60  is that the assembly  60  can be configured to be either a direct light source or an indirect light source. 
     Although the present invention has been described in considerable detail with reference to certain configurations thereof, other versions are possible. The assembly according to the invention can be many different sizes, can be in different types of housings, and can be used in many different configurations. Therefore, the spirit and scope of the invention should not be limited to the versions described above.