Patent Publication Number: US-8540402-B2

Title: LED housing with heat transfer sink

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional of U.S. Provisional Patent Application 61/347,450, filed May 23, 2010, and titled LED HOUSING WITH HEAT TRANSFER SINK, which is entirely incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention relates to thermal management for light sources, and particularly, to a heatsink for transferring and dissipating heat from a light source through a light housing. 
     Managing the temperature of light sources is often important to performance and longevity. This is particularly true when LEDs are used as a light source. LEDs are generally selected to maximize the light output for a given power consumption. Because LED light sources operate at a much lower temperature than typical incandescent light sources, less energy is wasted in the form of heat production. However, LEDs tend to be more sensitive to operating temperature and the lower operating temperatures also provide a much smaller temperature difference between the LED and the ambient environment, thus requiring greater attention to thermal management to transfer and dissipate any excess heat generated by the LED so that the design operating temperature for the LED light source is not exceeded. 
     As temperatures rise the efficacy of the LED is reduced, reducing the light output. Also, increased operating temperature of the LED reduces the lifespan of the LED. The LED driver is also affected by heat generated by the assembly (LED, driver, external factors). As the temperature rises within the assembly, raising the driver temperature, the lifespan of the driver is adversely affected causing premature failure. Operating at temperatures above the design limits can also cause LEDs to shift in wavelength providing undesirable shifts to the color of the light generated, can damage the LED junction greatly reduce the longevity and performance, and can potentially cause early complete failure of the LED. To facilitate dissipation of heat, it is helpful to increase the surface area available for heat transfer and to transfer the heat generated by the LED to the environment around the light housing. To achieve excellent heat transfer, it is also necessary to ensure that an excellent thermal coupling is provided from the light source to the exterior of the light housing. 
     SUMMARY 
     The present invention may comprise one or more of the features recited in the attached claims, and/or one or more of the following features and combinations thereof. 
     An illustrative thermally managed light includes a light source, for example an LED array, mounted inside a housing. The housing includes a disk-shaped heatsink thermally coupled to the light source. The heatsink has a conically tapered periphery shaped to match a conically tapered interior of the housing. A coupling device, for example a bracket and screw, hold the periphery of the heatsink in thermal contact with the interior of the housing, thus providing a heat transfer path from the light source to the ambient environment around the housing. 
     An illustrative thermally managed light includes a light source, a disk-shaped heatsink having an annulus with a conical outer surface and a central web spanning at least a portion of the annulus, the light source thermally coupled with the heatsink, a housing having a conical interior surface, a front opening for receiving the light source and the heatsink, and a rear end opposite the opening, and a tensioning device coupling the heatsink and the rear end of the housing. The tensioning device is adapted to retain the conical outer surface of the annulus in thermal contact with the conical interior surface of the housing. The light source can be thermally coupled with the central web of the heatsink. The light source can include at least one LED. 
     Another illustrative embodiment of a thermally managed light includes a light source, a heatsink having a tapered outer surface, the light source thermally coupled with the heatsink, a housing having an interior surface, at least a portion of the interior surface tapered to receive the tapered outer surface of the heatsink, and a coupling device securing the heatsink with the housing such that the tapered outer surface of the heatsink is thermally coupled with the tapered interior surface of the housing. 
     In one illustrative embodiment, the coupling device provides tension to the heatsink and is a U-shaped bracket and a screw, the bracket having two ends and a base, the two ends coupled to opposite edges of the heatsink and the base tensioned toward the end of the housing, thus pulling the tapered outer surface of the heatsink in thermal contact with the tapered interior surface of the housing, for example, direct mechanical contact, or only separated by a thermal grease or other thermally conductive material. The interior surface of the housing can be conical and taper inwardly toward the rear end of the housing. The outer surface of the heatsink can be conical and taper inwardly from the side facing the light source to the side facing the rear end of the housing. 
     The light can further include an LED driver positioned between the heatsink and the rear end of the housing. The LED driver can include a mounting plate coupled between the heat sink and U-shaped bracket. The light can further include a reflector. The light can further include a lens and glare shield. The heat sink can be formed from an aluminum casting. The light can further include a mounting device adjacent the rear end of the housing. 
     Additional features of the disclosure will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description particularly refers to the accompanying figures in which: 
         FIG. 1  is a cut-away side assembly view of an illustrative embodiment of a thermally managed light, with the near wall of the light housing shown cut-away; 
         FIG. 2  is an exploded rear view of the thermally managed light of  FIG. 1 ; and 
         FIG. 3  is a partially exploded front perspective view of the thermally managed light of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
     For the purposes of promoting and understanding the principals of the invention, reference will now be made to one or more illustrative embodiments illustrated in the drawings and specific language will be used to describe the same. 
     Referring to  FIG. 1 , an illustrative embodiment of a thermally managed light  10  according to the present disclosure includes a light source  12  mounted inside a housing  14 . The light source can be, for example, an LED array having one or more emitting elements. The housing  14  can be bullet-shaped, for example, such as for a flood or spot light used, for example, for lighting landscaping, or other housing shapes known in the art. The housing  14  also encloses a reflector  16 , heatsink  18 , an LED driver  20  and mounting plate  22 , and coupling device  24 . The light  10  also can include a glare shield  26 , lens  28 , and mount  30 . 
     In the illustrative embodiment, the heatsink  18  is disk-shaped and includes an outer rim or annulus  40  and a central web  42  spanning at least a portion of the depth of the annulus. In some embodiments, the heatsink  18  comprises a solid disk rather than having a web spanning a portion of the depth of the outer annulus. The light source  12  is thermally coupled with the heatsink  18 , for example, to the front surface  44  of web  42 . Thermal coupling may be further facilitated by thermally conductive grease, glue, or other material(s) located between the light source  12  and heatsink  18 . The thermal coupling may also be retained by alternative or additional mechanical action, for example by screws  50  securing light source  12  to the heatsink  18 . Such thermally conductive materials and mechanical action may also be included at other thermal couplings of the fixture, including those described below. In the illustrative embodiment, the entire heatsink  18  is encapsulated by the housing  14  and other components of the light  10 . 
     The annulus  40  includes an outer surface  46  that is tapered, in this embodiment conically shaped, with a larger diameter toward an opening  52  in the housing  14  and tapering toward a rear end  54  of the housing  14 . At least a portion of the housing  14  includes a matching tapered interior surface  56  for mechanically receiving and thermally coupling the outer surface  46  of the heatsink  18 , thus facilitating thermal dissipation of the heat transferred from the light source  12  to the housing  14  and into the air or other environment surrounding the housing  14 . The interior surface  56  portion of the housing  14  receiving the annulus  40  is similarly sized and tapered to receive the outer surface  46 , in this embodiment, conically shaped. Alternatively, the taper of the heatsink  18  and interior surface  56  of the housing  14  can be reversed in that the larger diameter is toward a rear end  54  of housing  14  in embodiments having a rear housing opening for receiving the heatsink  18 . 
     The heatsink  18  may also include standoffs  60  for supporting and/or spacing relative to reflector  16 . Such standoffs may optionally be designed to provide heat transfer. The heatsink  18  may also include or couple to standoffs  62  for supporting and/or spacing relative to plate  22 , and may similarly optionally be designed to provide heat transfer, and/or to secure heatsink  18  to the housing  14 . In the case of the illustrative embodiment of the light  10 , standoffs  62  provide the point of mechanically securing coupling device  24  to the heatsink  18 , although other points of securing can be used. Additionally, in the illustrative embodiment of light  10 , the heatsink  18  has an annulus  40  having a depth greater than the thickness of web  42 , thus providing a larger contact area for thermal transfer between the heatsink  18  and the housing  14  than would be provided by the web  42  alone contacting the housing  14 . 
     Referring to  FIGS. 1 and 2 , the coupling device  24  draws the heatsink  18  toward the rear end  54  of the housing  14 , thus ensuring thermal coupling of the outer surface  46  of the heatsink  18  with the interior surface  56  of the housing  14 . In the illustrative embodiment of the light  10 , the coupling device  24  includes a U-shaped bracket  70  and a draw screw  72 . The bracket  70  includes two ends  74  and a base  76 . The two ends  76  of bracket  70  are coupled to opposite segments of the heatsink  18  via screws  80  secured to standoffs  62 . The base  76  of the bracket  70  includes threaded receptacle  78  for receiving and securing the draw screw  76 . 
     As can be understood from the various drawings, the screw  72  passes from outside the housing  14  through opening  58  defined in the rear end  54  of the housing and draws the bracket  70 , and thus the heatsink  18 , toward the rear end  54  as the screw  72  is threaded further into the receptacle  78 . The bracket  70  is sized so that the outer surface  46  of heatsink  18  is drawn securely against the interior surface  56  of the housing  14  before the base  76  of the bracket  70  contacts the housing at the interior at rear end  54 . As also can be noted from the various drawings, in the illustrative embodiment of the light  10 , the interior of housing  14  lacks any limiting feature blocking the drawing of the heatsink  18  toward the rear end  54  of housing  14  other than the mechanical interference of the outer surface  46  of the heatsink  18  with the interior surface  56  of the housing  14 ; however, in alternative embodiments, such a feature could be included. 
     Alternative mechanical means of maintaining thermal contact between heatsink  18  and the interior surface  56  of housing  14  may also be used. For example, coupling device  24  can comprise alternative types of releasable and/or non-releasable fasteners, including, but not limited to a rivet. Alternatively, coupling device  24  may be integral with housing  14  or heatsink  18 , for example, a threaded component, the threads of which can be used to tension or press one of housing  14  and heatsink  18  into tight, and therefore thermal, contact with the other, ensuring the entire outer surface  46  of heatsink  18  is in contact with interior surface  56  of housing  14 . Additionally, coupling device  24  can be completely contained within the housing  14  with the pressing or drawing of heatsink  18  into housing  14  provided during the manufacturing process, and the coupling device  24  retaining the two in relative position, for example, via a tensioning element of the device  24 , for example, a spring. Additionally, or alternatively, one or more screw or other fasteners may extend from the front surface  44  of and through heatsink  18  to secure to an anchor point of the housing  18 , such as feature  90 , thus drawing heatsink  18  into mechanical and thermal contact with interior surface  56 . Additional or alternative coupling devices known in the art may be utilized. 
     In the illustrative embodiment of light  10 , the interior of housing  14  includes positioning features  90  and  92  receiving and stabilizing component plate  22 . Additionally, the spacers  62  and optional non-thermally conductive material used for plate  22 , for example, typical PCB material, can provide thermal isolation between the light source  12  and the driver  20 . 
     The material used for at least a portion of heatsink  18  is preferably highly thermally conductive, for example aluminum or an alloy. The material used for at least a portion of housing  14  is also preferably highly thermally conductive, for example aluminum, steel, or another alloy. In some embodiments, the exterior surface of housing  14  may include additional features to dissipate heat, for example, fins or other such structures that increase surface are and increase heat dissipation. 
     While the invention has been illustrated and described in detail in the foregoing drawings and description, the same is to be considered as illustrative and not restrictive in character, it being understood that only illustrative embodiments thereof have been shown and described and that all changes and modifications that come within the spirit and scope of the invention as defined in the claims and summary are desired to be protected.