Patent Publication Number: US-2022211016-A1

Title: Habitat lighting assembly

Description:
CLAIM(S) OF PRIORITY AND CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. patent application Ser. No. 16/392,926 filed Apr. 24, 2019, now U.S. Pat. No. 11,284,606, which claims the benefit of priority of U.S. Provisional Application No. 62/661,715 filed Apr. 24, 2018, the complete disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a habitat lighting assembly, a habitat including a lighting assembly, and related methods. 
     BACKGROUND 
     Animal and plant habitats, for example aquariums, terrariums, green houses, etc., are environments housing one or more species of flora and/or fauna, such as fish, invertebrates, amphibians, marine mammals, turtles, plants or any combination thereof. These species require diligent care which includes specific control of environmental conditions within the habitats. Environmental conditions such as temperature, light wavelength and intensity, salinity, and flow control of air or water inside the habitat are regulated to accommodate for the sustainability or growth of the particular species living therein. Optimum conditions will vary from species to species. 
     One component of controlling the environmental conditions in a habitat is the amount and type of light. Standard lighting units typically utilize light emitting diodes (LEDs), and fluorescent or metal halide bulbs that produce light at a specific spectrum and intensity. These lights may be hung above the habitat or be part of a hood or other unit which connects directly to the habitat. Typical lighting units are designed to shine light downward to permit a user to observe the habitat and to sustain life within the habitat. LED lighting units are desirable because the spectrum they output can be adjusted using combinations of discrete colors. 
     A problem with standard lighting LED units is that the polychromatic light sources of typical lighting units each act as an independent “point light sources,” which, when refracted through the moving surface of the water, create bands of light called “caustics” of different colors that are separated from each other. The separated caustics can lead to an effect in the habitat that can act as a distraction to the viewer. One way of reducing these banded caustics is to increase the number of LEDs or add a diffuser; however, doing so can increase energy costs, cause the lighting fixture to become overly large, and/or cause overheating of the lighting unit and/or of the habitat. 
     Further, the amount of light required by certain habitat species for sustaining life, such as through photosynthesis, can be relatively high, requiring a high energy density for the LEDs. LEDs operated at high power can overheat. As LEDs become hotter, their efficacy decreases, so that less light is provided to the habitat species for survival functions such as photosynthesis. 
     SUMMARY OF THE INVENTION 
     The disclosed invention is a LED lighting assembly for a habitat that has a light guide assembly having a plurality of integrated optical elements that diffuse the emitted light in order to eliminate caustics, particularly in an aquarium habitat. 
     According to a first aspect of the invention, a habitat lighting assembly includes a light guide having opposite first and second major surfaces and at least one edge surface extending between the first and second major surfaces. A solid-state light source is arranged to emit light into the edge surface of the light guide. A plurality of integrated optical elements is associated with the first major surface for redirecting the light from the solid-state light source. 
     According to a second aspect of the invention, a habitat lighting assembly includes at least an outer housing, an air circulation device configured to generate a flow of air into the outer housing through an air intake opening and out of the outer housing through an air discharge opening of the outer housing, a light guide comprising opposite first and second major surfaces and at least one edge surface extending between the first and second major surfaces, a solid-state light source arranged to emit light into the edge surface of the light guide, a plurality of integrated optical elements associated with the first major surface configured to redirect the light emitted by the solid-state light source, and a heat transfer system configured to transfer heat generated by the solid-state lighting source to the flow of air generated by the air circulation device. 
     A third aspect of the invention is a habitat lighting assembly including at least a light guide comprising opposite first and second major surfaces and at least one edge surface extending between the first and second major surfaces, a solid-state light source arranged to emit light into the edge surface of the light guide and comprising light-emitting diodes, laser diodes, organic light emitting diodes, or any combination thereof configured to produce multiple colors, and a plurality of integrated optical elements associated with the first major surface configured to direct light emitted by the solid-state light source upward toward the light reflector and/or downward. 
     A fourth aspect of the invention is a combination of a habitat and the habitat lighting assembly of any one of the first, second, or third aspects. 
     Other aspects of the invention, including apparatus, devices, kits, habitats, combinations, methods, processes, and the like which constitute part of the invention, will become more apparent upon reading the following detailed description of the exemplary embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
       The accompanying drawings are incorporated in and constitute a part of the specification. The drawings, together with the general description given above and the detailed description of the exemplary embodiments and methods given below, serve to explain the principles of the invention. In such drawings: 
         FIG. 1  is a perspective view of a habitat equipped with a lighting assembly according to an exemplary embodiment; 
         FIG. 2  is a top perspective view of the lighting assembly of  FIG. 1 ; 
         FIG. 3  is bottom perspective view of the lighting assembly of  FIG. 1 ; 
         FIG. 4  is a top perspective view of the lighting assembly of  FIG. 1  with a housing of the lighting assembly partially cut away; 
         FIG. 5  is a top perspective view of the lighting assembly of  FIG. 1  in a partially disassembled state with the light assembly housing not shown; 
         FIG. 6  is a side perspective, partially cut-away view of the lighting assembly of  FIG. 1 ; 
         FIG. 7  is a side perspective, partially cut-away view of parts of the lighting assembly of  FIG. 1 ; 
         FIG. 8  is a top perspective view of a light guide of the lighting assembly of  FIG. 1 ; 
         FIG. 9  is an enlarged fragmented view of oval  9  of  FIG. 7 ; 
         FIG. 10  is a cross-sectional view of the lighting assembly of  FIG. 1  taken along sectional line  10 - 10  of  FIG. 5 ; 
         FIG. 11  is a horizontal cross section of the lighting assembly of  FIG. 1  taken along sectional line  11 - 11  of  FIG. 10 ; 
         FIG. 12  is a top perspective, partially disassembled view of a lighting assembly according to another embodiment of the invention; 
         FIG. 13  is an enlarged fragmented view of a light guide according to another embodiment of the invention; 
         FIG. 14  is an enlarged fragmented view of a light guide according to still another embodiment of the invention; and 
         FIG. 15  is a perspective view of a habitat equipped with a lighting assembly according to another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS AND EXEMPLARY METHODS 
     Reference will now be made in detail to the exemplary embodiments and exemplary methods as illustrated in the accompanying drawings, in which like reference characters designate like or corresponding parts throughout the drawings. It should be noted, however, that the invention in its broader aspects is not necessarily limited to the specific details, representative materials and methods, and illustrative examples shown and described in connection with the exemplary embodiments and exemplary methods. 
       FIG. 1  depicts a habitat  15  according to an exemplary embodiment of the invention. In a particularly preferred embodiment, the habitat  15  is an aquatic habitat such as a marine aquarium (e.g., fresh water or salt water), though aspects of the invention may extend to other embodiments using non-aquatic habitats. For example, the lighting assemblies embodied and described herein can be used as a light source for a wide variety of habitats, including those containing flora and/or fauna, such as fish, invertebrates, amphibians, marine mammals, turtles, plants or any combination thereof. 
     The habitat  15  includes a container or tank  16  having a pair of opposite side walls  17  and  18  spaced apart from one another and a pair of spaced end walls  19  and  20  extending between opposite side edges of the side walls  17  and  18 . The tank  16  has a bottom wall  22  and a top opening  24  surrounded and defined by the top edges of the walls  17 ,  18 ,  19 , and  20  to provide a habitat enclosure. A cover, such as sliding panels  23 , may be placed over all or a portion of the top opening  24 . The cover  23  may be either integral with or connected to the tank  16 . The cover  23  may be transparent or provided with openings, such as a screen or grate. Though depicted as having a standard rectangular cross-sectional shape, the tank  16  may have different sizes, shapes, and configurations while including any number of walls. The walls  17 - 20  may be flat as shown, or they may be curved. The walls  17 - 20  of the tank  16  may be made from a variety of materials, especially transparent materials, including glass or plastics such as high-strength acrylics. 
     Components, such as pumps, fans, filters, etc., may be attached to or used in connection with the habitat  15  to alter or control the environment within the tank  16  or other type of enclosure. Depending on the organisms living in the habitat  15 , different combinations of components may be appropriate. In the exemplary embodiment illustrated in  FIG. 1 , the habitat  15  includes multiple pumps  26 , with each of the pumps  26  located on a respective one of the side walls  17  and  18  and the end walls  19  and  20  in the illustrated embodiment. The habitat  15  may also include a filter  28  and a heater  29 . These components may collectively affect specific environmental conditions to the habitat  15 . For example, the pumps  26  can create different flow types to mimic natural tides. 
     A lighting assembly  30  is suspended by suspension system  31 , which is illustrated in  FIG. 1  as comprising cables anchored to the ceiling (not shown). Alternatively, a floor stand or a tank-mounted bracket can be used to suspend the lighting assembly  30 , or the lighting assembly  30  can be connected to, supported on, or integrated into the top of the tank  16 .  FIG. 15  shows one or more brackets  31   a  attachable to the top or sides of the tank  16  to suspend the lighting assembly  30  over the top of the tank  16 . 
       FIGS. 2-10  depict an exemplary embodiment of the lighting assembly  30 . The lighting assembly  30  includes an outer housing  32  that may be made of metal, plastic, composite, or other material. As best shown in  FIG. 2 , the outer housing  32  includes an upper surface  33 , which can be part of a cover separable from and reattachable to the remainder of the outer housing  32 . The upper surface/cover  33  has an air intake opening  33   a  embodied as a circular opening. As best shown in  FIG. 3 , the outer housing  32  further includes a lower surface or base  34  with a light-transmissive opening  34   a  embodied as a rectangle. The light-transmissive opening  34   a  may be an empty space or may have a transparent window. Side walls and end walls  35  extend between the upper surface/cover  33  and the lower surface/base  34 . The end walls  35  include air discharge openings  35   a.  An air circulation device such as an impeller or fan  36  is positioned below the air intake opening  33   a.  The fan  36  draws air into the outer housing  32  through the air intake opening  33   a,  and the air exits the outer housing  32  through the air discharge openings  35   a.  The fan  36  may be mounted, such as with a bracket (not shown), to the cover  33 . 
     As best shown in  FIGS. 6, 8, 10, and 11 , the lighting assembly  30  includes a light guide  40  embodied as a plate having a first major surface  41  ( FIG. 10 ) facing upward and a second major surface  42  ( FIG. 10 ) facing downward and opposite to the first major surface  41 . The first and second major surfaces  41  and  42  are planar and parallel to one another. The first and second major surfaces  41  and  42  are parallel to one another, spaced apart, and define the thickness of the light guide  40 . The thickness is less than the length and width of the major surfaces  41  and  42 . Preferably, the thickness is uniform (with the possible exception of locations of optical elements  48  described below) over the entire length and width of the major surfaces  41  and  42 . For example, the thickness may be in a range of 3.0 mm to 8.0 mm, such as 6 mm. 
     As best shown in  FIGS. 8 and 11 , the light guide  40  includes side (lateral) edge surfaces  43  and  44  extending between the first and second major surfaces  41  and  42 , and end edge surfaces  45  and  46  extending between the first and second major surfaces  41  and  42  and perpendicular to the side edge surfaces  43  and  44 . End edge surfaces  45  and  46  of the light guide  40  are parallel to one another and spaced apart from one another by the length of the light guide  40 . The side edge surfaces  43  and  44  are parallel to one another and spaced apart from one another by a width of the light guide  40 . 
     While the light guide  40  is shown generally rectangular in shape, it should be understood that the light guide  40  may possess alternative shapes, such as that of a square or another polygonal shape. Any one or more of the edge surfaces  43 ,  44 ,  45 , and/or  46  of the light guide  40  may be curved or non-linear. The thickness of the light guide  40  may vary so as to be non-uniform. Although the lighting assembly  30  is shown with a single light guide  40 , it should be understood that the lighting assembly  30  alternatively may be provided with multiple light guides  40  layered one on top of another and/or in side-by-side arrangement. 
     The light guide  40  is preferably made of an optically transmissive material. Exemplary materials include plastics such as acrylics (e.g., polymethylmethacrylate PMMA), polycarbonates, and/or liquid silicone rubber (LSR). The light guide  40  may rest on the base  34  of the outer housing  32  or otherwise be secured to the outer housing  32 . 
     First and second light source holders  50  and  51  are spaced apart from one another, one opposite sides of the light guide  40  adjacent to the side edge surfaces  43  and  44 , respectively, as best shown in  FIGS. 10 and 11 . For the purposes of this embodiment, the first and second light source holders  50  and  51  are identical to one another, although it should be understood that they may differ. The light source holders  50  and  51  may be supported on or attached to a support base  63  ( FIG. 9 ). Alternatively, the light source holders  50  and  51  may be attached directly to the light guide  40  or to the outer housing  32  using, for example, mechanical fasteners, adhesive, bonding, welding, etc. The light source holders  50  and  51  may be part of a frame surrounding the light guide  40 . The light source holders  50  and  51  may be made of metal (e.g., aluminum), plastic, or another material. As best shown in  FIG. 9 , the first light source holder  50  can include light reflective linings  50   a.  The light reflective linings  50   a  can be made of cut pieces of reflective material, such as paper, coated paper, plastic, metal coated plastic, metal foil, etc., or a combination thereof. The surfaces of the light reflective linings  50   a  preferably are white or silver. Although not shown, the second light source holder  51  can include similar light reflective linings. 
     As best shown in  FIG. 10 , the first and second light source holders  50  and  51  each have a U-shaped cross-section/profile with an opening extending along their respective lengths to face the side edge surfaces  43  and  44 , respectively, of the light guide  40 . One or more first light sources  52  are arranged along the first light source holder  50  so as to be adjacent to and emit and introduced light into the light guide  40  through the side edge surface  43  of the light guide  40 . One or more second light sources  53  are arranged along the opposite second light source holder  51  so as to be adjacent to and emit and introduced light into the light guide  40  through the side edge surface  44  of the light guide  40 . The light sources  52  and  53  are preferably solid-state light emitters, such as semiconductor light emitting diodes (LEDs), laser diodes, and/or organic light emitting diodes (OLEDs). 
     The first light source(s)  52  may comprise a plurality of LEDs or other solid-state light emitters mounted on a printed circuit board (PCB)  54  arranged at the opening of the first light source holder  50 . Likewise, the second light source(s)  53  may comprise a plurality of LEDs or other solid-state light emitters mounted on a printed circuit board (PCB)  55  arranged at the opening of the second light source holder  51 . Attachment of the PCBs  54  and  55  to the first and second light source holders  50  and  51  and/or to the light guide  40  may be accomplished using, for example, mechanical fasteners, adhesives, bonding, soldering, welding, etc. 
     The first light source  52  and the second light source  53  are arranged to emit light into the side edge surfaces  43  and  44 , respectively, so that the light propagates along the light guide  40  between the first and second major surfaces  41  and  42  of the light guide  40 . The first light source  52  and the second light source  53  preferably are arranged along substantially the entire length of the side edge surfaces  43  and  44 , respectively, to uniformly direct light into the opposite edge surfaces  43  and  44  of the light guide  40 . 
     Alternative arrangements of light sources are possible. For example, the lighting assembly  30  may include fewer or more LEDs in the first and second light sources  52  and  53  than depicted in the drawings. The number of first light source LEDs  52  associated with the side edge surface  43  may be the same as or different than the number of second light source LEDs  53  associated with the side edge  44 . While the light sources  52  and  53  are arranged adjacent opposite side edge surfaces  43  and  44  of the light guide  40  in the exemplary embodiment described above, in an alternative embodiment the light sources  52  and  53  are arranged adjacent the end edge surfaces  45  and  46 . In another alternative embodiment, light sources  52  and  53  and additional light source (not shown) are respectively arranged along the edge surfaces  43 ,  44 ,  45 , and  46 . In yet another alternative embodiment, the light sources  52  and  53  are arranged along perpendicular edge surfaces, such as edge surfaces  43  and  45 . In still another alternative embodiment, only one of the light sources  52  or  53  is provided and arranged along one of the edge surfaces, e.g.,  43 ,  43 ,  45 , or  46 , with the other three edge surfaces not being associated with adjacent light sources. In a further alternative embodiment, light sources are arranged adjacent three edges surfaces, such as edge surfaces  43 ,  44 , and  45 , but not the fourth edge surface, e.g.,  46 . 
     Desirably, each of the light sources  52  and  53  includes multiple sets of LEDs (or OLEDs, etc.), with each of the LED sets of light sources  52  and  53  including multiple different color light sources, optionally including a white light source. Each color LED may be part of a single channel, so that the LEDs of the light sources  52  and  53  as a group provide a multi-channel light source. The light sources  52  and  53  may emit light in the non-visible spectrum, such as ultraviolet light and/or infrared light, if desired. The light sources  52  and  53  may be capable of emitting light over a range of intensities and wavelengths, or different light sources can be monochromatic or of a dedicated wavelength or intensity. In an exemplary embodiment, the light sources  52  and  53  emit light over ranges of wavelengths that are different or slightly overlap with one another. For example, the first and second light sources  52  and  53  may include different color groups of white, red, green, blue, royal blue, and/or violet. The wavelength of the light sources  52  and  53  may be individually controlled to selectively place them into an on-state or off-state to produce different colors, shades, and intensities of color. Each color group may be separated into an individual channel and controlled separately. Preferably the first and second light sources  52 ,  53  are capable of generating light that simulates natural sun light. 
     As best shown in  FIGS. 4-6 and 10 , a light reflector  60  is located adjacent to the upper first major surface  41  of the light guide  40 . The light reflector  60  may be in direct contact with or spaced apart from the first major surface  41 . The light reflector  60  may be a separate component from the light guide  40 , such as a plate. Alternatively, the light reflector  60  may be a coating or film applied on the light guide  40 . Preferably, the light reflector  60  extends at least the entire width and length of the light guide  40 . The light reflector  60  may be white, specularly reflective, or diffusely reflective, depending upon the desired light output. The light reflector  60  may be made of cut pieces of reflective material, such as paper, coated paper, plastic, metal coated plastic, metal foil, etc., or a combination thereof. 
     As best shown in  FIGS. 3, 6, and 10 , a diffuser  62 , such as in the form of a plate, film, or coating, optionally is positioned adjacent to the lower second major surface  42 , i.e., under the light guide  40 . The diffuser  62  preferably is coextensive with the light-transmissive opening  34   a.  The diffuser  62  is selected to diffuse the light emitted through the second major surface  42  to provide a more uniform, homogenous light output distribution. The diffuser  62  provides the secondary benefit of concealing the integrated optical elements  48  (discussed further below). The diffuser  62  can be, for example, a plastic, quartz, frosted, or translucent material or materials. An example of a suitable diffuser is a G-Series Glare Control Diffuser of Brightview Technologies. 
     At least one, and optionally both, of the first and second major surfaces  41  and  42  include integrated optical elements  48 . For example,  FIG. 8  illustrates the integrated optical elements  48  integrated into the first major surface  41 . The integrated optical elements  48  have a structure suitable for directing light, such as upward from the solid-state light sources  52  and  53  into the light reflector  60 , which reflects the light downward to pass through the optional diffuser  62  and the light-transmissive opening  34   a.  The integrated optical elements  48  may also or alternatively include structure suitable for directing light from the solid-state light sources  52  and  53  directly downward to pass through the optional diffuser  62  and the light-transmissive opening  34   a.  The integrated optical elements  48  may be convex, concave, cylindrical, prismatic, or a combination thereof. The integrated optical elements  48  may be arrayed in rows and columns. The density of integrated optical elements  48  can be uniform or varied over the first major surface  41  of the light guide  40 . The integrated optical elements  48  may be raised structures extending upward from the plane of the first major surface  41  or depressed structures extending downward below the plane of the first major surface  41 . The elements  48  may be a physical structure in the light guide  40 . For example, the elements  48  can be a screen-printed structure painted on the light guide  40  or a particulate material embedded in the light guide  40 . 
     The integrated optical elements  48  may be identical in shape and/or size to one another or may differ in shape and/or size from one another. For example, the integrated optical elements  48  may have an effective diameter of 1 mm to 1000 mm. In a particularly exemplary embodiment best illustrated in  FIG. 8 , the integrated optical elements  48  have the appearance of dots or dimples. The integrated optical elements  48  can be formed in or on the light guide  40  in any suitable manner, such as molding, embossing, screen printing, drilling, three-dimensional printing, etching, etc. While it is preferred that the integrated optical elements  48  have a three-dimensional structure extending into or out of the light guide  40 , the elements  48  may be formed by imprinting or otherwise depositing a material onto first major surface  41 , such as by screen printing, ink jet printing, etc. 
       FIG. 13  is an enlarged fragmented view of a light guide  40   a  having integrated optical elements  48   a  configured as cones that protrude outwardly from the surface of guide  40   a . The tops of the cones of the integrated optical elements  48   a  may be flat or curved (e.g., convex).  FIG. 14  is an enlarged fragmented view of a light guide  40   b  having integrated optical elements  48   b  configured as conical recesses that protrude inwardly from the surface of light guide  40   b . The bottoms of the conical recesses of the integrated optical elements  48   b  may be flat or curved (e.g., concave). Examples of other integrated optical elements  48  are described in U.S. Patent Publication No. 2013/0314944 (which uses the terms “deformities” and “optical deformities” and the like), the complete disclosure of which is incorporated herein by reference. 
     A representative material that may be used as the light guide  40  is a PMMA clear light guiding prismatic plate LGP provided by Jungbecker. The LGP decouples light which is fed into the light guide from the edges across the surface area by the use of the integrated microprismatic optics  48 . The LGP uses reflection and refraction of the microprisms to direct and “deglare” light. 
     Without wishing to be necessarily bound by any theory, it is believed that the integrated optical elements  48 ,  48   a,    48   b  of the light guide  40  cause light entering the light guide  40  to experience total internal reflection (“TIR”). The integrated optical elements  48 ,  48   a,    48   b  interact with the light entering through the edge surfaces of the light guide  40  and propagating therethrough to redirect and uniformly distribute the light so that it is emitted through the second major surface  42 . The reflector  60  causes any light which is directed upward by the integrated optical elements  48 ,  48   a,    48   b  to reflect downward and emitted through the second major surface  42 . At the same time, the integrated optical elements  48 ,  48   a,    48   b  reduce if not eliminate the color bands by homogeneously blending the light so that it is emitted as an incoherent and blended light appearing as a very diffused uniform spectrum. As a result, the need for an excess number of LEDs is avoided, which lowers manufacturing and operating costs and reduces the amount of heat generated by the LED light sources  52  and  53 . 
     In order to create a close approximation of a natural environment, the lighting assembly  30  may include a controller having the capability of providing diverse outputs such as different light intensities, different light patterns, different light colors, etc. Examples of different operating modes that may be selected by varying the outputs include night, sunrise, day, sunset, lunar colors, storms, and solar cycles. The lighting assembly  30  may be provided with a user interface (not shown) to allow programming of the operating modes. Alternatively, operating modes may be pre-programmed into the assembly  30  or may be remotely programmed by communicating with a receiver (not shown), such as a wireless communication device (e.g., Wi-Fi module), of the assembly  30 . 
       FIGS. 5 and 6  depict a block  64  housing, for example, controllers, microprocessors, circuitry, modules, drivers, and/or other electronic components (not shown but known in the art and described in U.S. Pat. No. 9,839,206) to control operation of the light sources and the pumps  26 . The circuitry/electronic components of the block  64  may include, for example, microcontrollers or microprocessors for receiving and processing data and providing output to control the components of the lighting assembly  30 . The microprocessor(s) may be connected to a driver that controls the output of the light sources, for example by varying the wavelength and intensity of individual or groups of light sources, by cycling on and off individual or groups of light sources, or through a combination of both. This allows the lighting assembly  30  to provide different lighting characteristics and patterns. Together with controlled water circulation via the pumps  26 , the conditions of the habitat  15  can be controlled to mimic day-and-night cycles and seasonal cycles by varying light intensity, color, and on/off state. In this manner, the overall light color emitted by the lighting assembly  30  may be controlled locally or remotely to promote the growth and health of specific organisms in the habitat  15 , such as plants, coral or anemones. 
     Light sources such as LEDs produce large amounts of heat that can adversely affect the efficacy of the LEDs and, in extreme circumstances, damage the electronics  64  and the PCBs  54  and  55  of the lighting assemblies  30  of the habitat  15 . Generally, the lighting assemblies of the type used with habitats  15  are relatively small and compact, and are unable to adequately disperse the heat generated by light sources such as LEDs. 
     According to an exemplary embodiment of the invention, heat insulators and/or a heat transfer system may be provided to protect the components  64  from the heat generated by operation of the light sources. As best shown in  FIGS. 4-7, 10, and 11 , the lighting assembly  30  includes a heat transfer system comprising one or more heat pipes  70  configured to transfer heat away from the heat sources, i.e., the light sources  52  and  53  such as LEDs, to baffles or fins  72  and  74  adjacent opposite end edge surfaces  45  and  46 , respectively, of the light guide  40 . The heat pipes  70  extend through passages  72   a  and  74   a  of the fins  72  and  74 . The heat pipes  70  carry the heat from the light sources  52  and  53  to the fins  72  and  74 , so that the heat is transferred to the fins  72  and  74 . Cooler air drawn through the air intake opening  33   a  into the lighting assembly  30  by the fan  36  is blown against the fins  72  and  74 . The large surface area provided by the fins  72  and  74  provides a large interface for the cool air to remove heat released from the heat pipes  70  and expel the resulting hot air through the air discharge openings  35   a.    
     An example of a suitable commercially available heat pipe is available from Cooling Technologies, Inc. (formerly HPEV), which advertises its heat pipes as passive (no moving parts or external power). According to Cooling Technologies, Inc., the heat pipe is a sealed tube with a layer of wick material surrounding a hollow core filled with fluid. Heat entering the sealed tube causes the fluid to vaporize and travel to the cooler end, which in the case of the embodied lighting unit will be the fins  72 , where the heat is released and the vapor condenses back into a fluid. 
     Other heat insulators and/or heat insulating systems may be used. For example, one or more vapor chambers may be included in the lighting assembly  30  to transfer heat away from the light sources  52  and  53 . 
     The lighting assembly  30  may be powered by an external power source, such as an AC source, in which case a rectifier or comparable AC/DC device may be used to rectify the alternating current (AC) to direct current (DC). A driver or drivers convert(s) constant voltage from the power supply to a constant current output with a voltage sufficient to overcome the “forward voltage” of the diode(s). Alternatively, a DC source such as a battery may be provided as the primary power source or as a backup secondary power source. 
     A lighting assembly according to another embodiment of the invention is generally indicated by reference numeral  130  in  FIG. 12 , in which like reference numerals of the first lighting assembly  30  of  FIGS. 1-10  are used to designate corresponding parts of the lighting assembly  130 , except with the addition of “100” to the reference numerals in  FIG. 12 . The above description of those corresponding parts of the lighting assembly  30  is incorporated herein by reference with respect to the description of the lighting assembly  130 . The lighting assembly  130  is generally the same as the lighting assembly  30 , except for the addition of a second fan  137 . Although not shown, the outer housing (not shown in  FIG. 12 ) of the lighting assembly  130  would be provided with an additional air intake opening identical to  33   a  to as to extend over the second fan  137 . 
     Assembly of the lighting assemblies  30  and  130  is within the purview of a person of ordinary skill in the art having reference to this disclosure. According to one exemplary embodiment, the cover  33  is separated from the remainder of the outer housing  32  to provide access to the internal cavity of the outer housing. The diffuser  62  is placed in the outer housing  32  and optionally secured to on the lower surface or base  34  to cover or fit within the light-transmissive opening  34   a.  The first and second light source holders  50  and  51  are arranged to receive the heat pipe  70 , and the printed circuit boards (PCB)  54  and  55  with the solid-state light sources  52  and  53  preinstalled are arranged at and secured to (e.g., solder, fastener, etc.) the opening of the first light source holder  50 . The resulting subassembly is placed in the outer housing  32 . If the support base  63  ( FIG. 9 ) is used, the light source holders  50  and  51  may be supported on or attached to the support base  63 . 
     The light guide  40  is placed in the outer housing  32  so that the solid-state light sources  52  and  53  are adjacent to side edge surfaces  43  and  44  of the light guide  40 . A reflector  60  is either pre-installed on the light guide  40  or is placed in the outer housing  32  on the first major surface  41  of the light guide  40 . The electronics block  64  is placed on the reflector  60 . The air circulation device/fan  36  may be secured to the cover  33  using a bracket (not shown), and the cover  33  is attached to the remainder of the outer housing  32 . 
     The various components and features of the above-described exemplary embodiments may be substituted into one another in any combination. It is within the scope of the invention to make the modifications necessary or desirable to incorporate one or more components and features of any one embodiment into any other embodiment. In addition, although the exemplary embodiments discuss steps performed in a particular order for purposes of illustration and discussion, the methods discussed herein are not limited to any particular order or arrangement. One skilled in the art, using the disclosures provided herein, will appreciate that various steps of the methods can be omitted, rearranged, combined, and/or adapted in various ways. 
     The foregoing detailed description of the certain exemplary embodiments has been provided for the purpose of explaining the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. This description is not necessarily intended to be exhaustive or to necessarily limit the invention to the exemplary embodiments disclosed.