Patent Publication Number: US-9416954-B2

Title: Light fixture with thermal management properties

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/688,068, filed May 7, 2012, the entirety of which is herein incorporated by reference. 
    
    
     FIELD 
     Embodiments of the present invention relate to a light fixture having thermal management properties. 
     BACKGROUND 
     Light emitting diodes (“LED”) are typically mounted on a printed circuit board (“PCB”) and wired to the PCB. LEDs generate a great deal of heat during operation, which, if not transferred from the LEDs, can detrimentally impact the efficiency of the LEDs. Heat generation in a closed fixture can be particularly problematic and removal of such heat from the fixture even more challenging. 
     SUMMARY 
     Certain embodiments of the present invention provide a light fixture having an electronic housing and at least one optical chamber positioned on each side of the electronic housing. In some embodiments, the optical chambers are positioned a distance from the electronic housing so as to avoid creation of a thermal path between the optical chambers and the electronic housing. Each optical chamber includes a heat sink and a plurality of LEDs mounted on a PCB that is, in turn, mounted on the heat sink. A reflector is positioned over at least a portion of the PCB. In some embodiments, vents extend through the heat sink and fins extend upwardly from the heat sink and angle at least partially over at least some of the vents. 
     In use, air enters the optical chambers and exits the fixture through the top vents in the heat sink. The air circulates over the reflectors, carrying heat from the reflectors during the process. Heat is also conducted to the air from the heat sink. The angled fins extending over the top vents provide additional surface area for contact with the air and thus facilitate additional heat transfer from the heat sink. 
     The terms “invention,” “the invention,” “this invention” and “the present invention” used in this patent are intended to refer broadly to all of the subject matter of this patent and the patent claims below. Statements containing these terms should not be understood to limit the subject matter described herein or to limit the meaning or scope of the patent claims below. Embodiments of the invention covered by this patent are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to the entire specification of this patent, all drawings and each claim. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Illustrative embodiments of the present invention are described in detail below with reference to the following drawing figures: 
         FIG. 1  is a bottom perspective view of one embodiment of a light fixture provided with the reflector of  FIGS. 12 a    and  12   b.    
         FIG. 2  is a top perspective view of the light fixture of  FIG. 1 . 
         FIG. 3  is a top plan view of the light fixture of  FIG. 1 . 
         FIG. 4  is a top plan view of an alternative embodiment of a light fixture. 
         FIG. 5  is another bottom perspective view of the light fixture of  FIG. 1 . 
         FIG. 6  is an enlarged view taken at inset circle  6  of  FIG. 5 . 
         FIG. 7  is a bottom perspective view of an embodiment of a heat sink. 
         FIG. 8  is a top perspective view of the heat sink of  FIG. 7 . 
         FIG. 9  is an enlarged view taken at inset circle  9  of  FIG. 8 . 
         FIG. 10  is a bottom perspective view of printed circuit boards with LEDs mounted to the heat sink of  FIG. 7 . 
         FIG. 11  is an enlarged view taken at inset circle  11  of  FIG. 10 . 
         FIG. 12 a    is a top perspective view of one embodiment of a reflector for use in a light fixture. 
         FIG. 12 b    is an end view of the reflector of  FIG. 12   a.    
         FIG. 13 a    is a top perspective view of another embodiment of a reflector for use in a light fixture. 
         FIG. 13 b    is an end view of the reflector of  FIG. 13   a.    
         FIG. 14  is a bottom perspective view of an embodiment of a light fixture provided with the reflector of  FIGS. 13 a    and  13   b.    
         FIG. 15  is an enlarged view taken at inset circle  15  of  FIG. 14 . 
         FIG. 16  is another enlarged view of the light fixture of  FIG. 14 . 
         FIG. 17  is yet another enlarged view of the light fixture of  FIG. 14 . 
         FIG. 18  is a side elevation view of the light fixture of  FIG. 14 . 
         FIG. 19 a    is a top perspective view of one embodiment of a side door frame. 
         FIG. 19 b    is a side elevation view of the side door frame of  FIG. 19   a.    
         FIG. 19 c    is an end view of the side door frame of  FIG. 19   a.    
         FIG. 20  is a bottom perspective view of yet another embodiment of a light fixture. 
         FIG. 21  is a top perspective view of the light fixture of  FIG. 20 . 
         FIG. 22  is a bottom perspective view of still another embodiment of a light fixture. 
         FIG. 23  is a bottom perspective view of an embodiment of a light fixture with the cover removed from the electronic housing. 
     
    
    
     DETAILED DESCRIPTION 
     The subject matter of embodiments of the present invention is described here with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described. 
     The Figures illustrate various views of embodiments of light fixture  10  contemplated herein. The light fixture  10  is designed to be suspended from a ceiling (such as with brackets or pendant hanger  2 ) but it is also contemplated that the light fixture can be recessed within a ceiling. 
     In the illustrated embodiment of  FIGS. 1-3 , the light fixture  10  is formed by two optical chambers  12  and an electronic housing  14  interposed between the optical chambers  12  for housing the electrical components  90  that drive the fixture (e.g., driver, battery pack(s), etc., shown in  FIG. 23 ). However, any number of optical chambers could be assembled to form the fixture  10 . By way only of example, multiple optical chambers  12  may be provided on each side of the electronic housing  14  and connected in series or otherwise, as shown in  FIG. 4 . 
     Each optical chamber  12  includes a heat sink  16 , LEDs  18  mounted on the heat sink  16 , and a reflector  20 ,  22 . An embodiment of the heat sink  16  is shown in isolation in  FIGS. 7-9 . The heat sink  16  may be formed from any thermally conductive material, such as metal, including steel, aluminum, etc. 
     The heat sink  16  within the optical chamber  12  is shown having two troughs  24  but it may have any number of troughs, including a single trough. Each trough  24  is defined by a planar portion  100  with an outer side arm  102  and an inner side arm  104  extending downwardly at an angle from the planar portion  100 . Top vents  26  are provided along the top of the heat sink  16 . In some embodiments, the top vents  26  are stamped from a metal sheet that is subsequently formed into the heat sink  16 . The metal stamped from the metal sheet is not completely severed. Rather, it remains connected to the sheet and is bent to create a fin  28  that extends upwardly from and angles inwardly over each top vent  26 . These fins  28  enhance heat dissipation from the fixture  10 , as discussed in more detail below. 
     LEDs  18  (mounted on a PCB  30 ) are mounted within the troughs  24  of the heat sink  16 , as shown in  FIGS. 10 and 11 . A reflector  20 ,  22  is then positioned over the LEDs. The reflector  20 ,  22  includes apertures  32  such that, when the reflector  20 ,  22  is positioned over the LEDs  18 , each LED  18  is positioned within an aperture  32  in the reflector  20 ,  22  so as to be able to emit light from the optical chamber  12 . Thus, the PCB  30  is sandwiched between, and protected by, the heat sink  16  and the reflector  20 ,  22 . Because of the protection afforded the PCB  30 , the PCB  30  can be, but need not be, a metal-core board but rather less expensive boards may be used. 
     Different reflector geometries are contemplated and are certainly not intended to be limited to the precise geometries depicted in the figures. A first embodiment of a reflector  20  is shown in isolation in  FIGS. 12 a  and 12 b    and incorporated into a light fixture  10  in  FIGS. 1, 5, and 6 . Reflector  20  includes a substantially flat top portion  34  that seats over the PCB  30  and angled side walls  36  that extend downwardly from each side of the top portion  34 . 
     A second embodiment of a reflector  22  is shown in isolation in  FIGS. 13 a  and 13 b    and incorporated into a light fixture  10  in  FIGS. 14-17 . Reflector  22  includes a substantially flat top portion  40  that seats over the PCB  30 , angled side walls  42  that extend downwardly from each side of the top portion  40  (although not necessarily at the same angle from each side of the top portion  40 ), and a ledge  44  that extends from one of the angled side walls  42 . The ledge  44  includes upwardly extending arms  46  spaced along the length of the ledge  44 . When the reflector  22  is properly positioned on the heat sink  16  over the LEDs  18 , the upwardly extending arms  46  engage slots  48  located in the heat sink  16 . See  FIG. 17 . A gap  50  is formed between the heat sink  16  and the reflector  22  between adjacent upwardly extending arms  46 , as seen in  FIGS. 17 and 18 . Multiple gaps  50  may be formed in this way along the length of the optical chamber  12 . 
     The reflectors  20 ,  22  may be formed of any suitable thermally conductive material, including metal such as painted steel or aluminum. In use, heat generated by the LEDs  18  is conducted both to the heat sink  16  behind the PCB  30  and the reflector  20 ,  22  positioned over the PCB  30 . Thus, the reflector  20 ,  22  effectively acts as a heat sink as well. 
     The light fixture  10  may be used as an open fixture (i.e., the optical chambers  12  remain open and air is free to enter each chamber  12  from below, as shown in  FIGS. 1 and 14 ) or a lens  52  may be positioned over each optical chamber  12  to enclose each chamber  12 , such as shown in the embodiment of  FIG. 20 . In the open fixture situation, cooler air enters the optical chambers  12  from below the fixture  10  and exits the fixture  10  through the top vents  26  in the heat sink  16 . The air circulates over the angled side walls  36 ,  42  of the reflectors  20 ,  22 , carrying heat from the reflectors  20 ,  22  during the process. In this way, the reflectors  20 ,  22  operate as heat sink fins. Heat is also conducted to the air from the heat sink  16 . The angled fins  28  extending over the top vents  26  provide additional surface area for contact with the air and thus facilitate additional heat transfer from the heat sink  16 . 
     Thus, heat dissipation from the fixture  10  results both from conduction of heat from the LEDs  18  via the reflectors  20 ,  22  and the heat sink  16  as well as conduction and convection of heat from the reflectors  20 ,  22  and the heat sink  16  to the air circulating through and around the reflectors  20 ,  22  and heat sink  16 . Such air consequently heats up and rises, thereby carrying heat away from the fixture  10  through the top vents  26  via convection. 
     It is also possible to enclose the optical chambers  12 , such as with a lens  52 . See  FIG. 20 . However, then alternative paths must be provided to permit air ingress into the optical chambers  12  to facilitate cooling.  FIGS. 19 a -19 c    show in isolation an embodiment of a side door frame  54  that is used (i) to help retain a lens  52  over an optical chamber  12  and (ii) for thermal management purposes. A side door frame  54  is positioned on the sides of the heat sink  16 , as shown in  FIGS. 20 and 21 . The side door frame includes a ledge  56  (see  FIG. 19 c   ) upon which the lens  52  rests when the side door frame  54  is so positioned. In this way, the side door frame  54  supports and helps retain the lens  52  on the fixture  10 . 
     In the illustrated embodiment, the side door frames  54  are retained on the heat sink via tabs  60  on the side door frames  54  engaging slots  62  in the heat sink  16 . However, the side door frame  54  may be mounted on the heat sink  16  using a variety of other mechanical retention methods. 
     Vents  66  may be located along the length of each side door frame  54 . Such vents  66  permit air to enter each optical chamber  12 , which is closed by virtue of the lens  52 . If reflector  20  is used, the air is free to enter the chamber  12 . If reflector  22  is used, the vents  66  align with the gaps  50  formed between the heat sink  16  and the reflector  22  so that air can easily flow into the chamber  12  for convective cooling, as described above. The vents  66  on the side door frame  54  may be angled or punched inwardly to prevent light from escaping through such vents  66 , thus preventing the undesirable glare such light would cause to inhabitants below. 
     End caps  80  may be provided at the ends of the optical chambers  12  and the electronic housing  14  to hold the components together. Moreover, a wire guard  70  (see  FIG. 22 ) may be positioned on the fixture  10  to protect the fixture  10 , although inclusion of a wire guard  70  is entirely optional. 
     In some embodiments, the electronic housing  14  is interposed between each optical chamber  12 . While not necessary, it may be desirable that each optical chamber  12  be spaced a distance from the electronic housing  14  to prevent creation of a thermal path between the optical chambers  12  and the electronic housing  14  and thereby thermally protect the electronics contained within the electronic housing  14 . Air gaps  72  formed between the electronic housing  14  and the optical chambers  12  are seen in  FIG. 3 . The electronic housing  14  may also contain vents  74  for convective cooling purposes. In some embodiments (see  FIG. 23 ), heat spreaders  92  are provided on some or all of the electronic components  90  housed in the electronic housing  14 . Moreover, one or more active cooling systems  94 , such as a fan or synthetic jet actuator (such as SynJet® cooling technology, available from Nuventix), may be provided within the electronic housing  14  and used to blow air across the heat spreaders  92  to help dissipate heat from the electronic components  90  and from the electronic housing  14 . A cover  76  encloses the electronic housing  14  and is easily removable from below to access the electronics  90  without having to remove the lenses  52  (if lenses are provided). 
     The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of the present invention. Further modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the invention. Different arrangements of the components depicted in the drawings or described above, as well as components and steps not shown or described are possible. Similarly, some features and subcombinations are useful and may be employed without reference to other features and subcombinations. Embodiments of the invention have been described for illustrative and not restrictive purposes, and alternative embodiments will become apparent to readers of this patent. Accordingly, the present invention is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications can be made without departing from the scope of the invention.