Patent Publication Number: US-7914182-B2

Title: Decorative light fixture including cooling system

Description:
BACKGROUND 
     Decorative light fixtures typically include an attractive housing with a light source that is typically a metal halide lamp or a halogen lamp or an incandescent lamp. These light fixtures work well, but can be improved by using a more efficient and longer lasting light source. 
     Light emitting diodes (LEDs) can provide a bright, longer lasting light engine as compared to a metal halide lamp or a halogen lamp. LEDs, however, generate a great amount of heat that needs to be dissipated to provide a bright, long lasting light engine. Dissipating this heat can be difficult where it is desirable to use an attractive housing that is similar in configuration to the known decorative housings used with metal halide or halogen lamps. 
     A known decorative light fixture that employs an LED light engine in a conventional attractive housing, i.e., one that would typically include a metal halide or halogen lamp, conducts heat generated by the LEDs either into a pole upon which the light fixture is mounted or maintains the heat within a glass enclosure that forms a part of the housing. Either situation limits the amount of power that can be delivered to the LEDs. This is due to the pole typically not being a very good heat conductor or that the heat maintained within the glass enclosure results in heat still being maintained in a volume that is adjacent the LEDs. Furthermore, where the heat is dissipated into the pole upon which the light fixture is mounted, the pole can get hot. Also, for light fixtures where no pole is provided, e.g. a pendent light fixture, there is no pole which can act as a heat sink. 
     Another drawback with known attractive light fixtures that employ an LED light engine is that the LEDs are point light sources, which are visible when viewing the light fixture from horizontal. When these point light sources are visible, this can result in an unattractive look for the light fixture. 
     SUMMARY 
     A decorative light fixture that overcomes the aforementioned shortcomings includes a light engine and a shroud. The light engine includes a heat sink and a light source in thermal communication with the heat sink. The shroud covers the light engine to define an air path between an air inlet and an exhaust. The air inlet is disposed vertically below the exhaust. The air path is shaped to direct air over the heat sink and to exit the shroud above the light engine. 
     The air inlet and the exhaust can each be in communication with ambient. The area of the air inlet can be at least about 20% larger than the area of the exhaust. The area of the exhaust can be less than about 30% larger than the area of the air inlet. The shroud can define a central axis and a cross sectional area normal to the central axis of a volume surrounded by the shroud adjacent the air inlet can be greater than the cross-sectional area normal to the central axis of the volume adjacent the outlet. 
     The heat sink can include a base and fins. The fins can extend upwardly from the base and radiate from the central axis. The heat sink can further include a central pillar coaxial with the central axis that extends upwardly from and normal to the base. Some fins can have internal edges that are contiguous with the pillar and some fins can have internal edges that are spaced from the pillar. The heat sink can also include fins where the cross-sectional area normal to the central axis of an envelope, which is the area surrounded by the shroud less the area occupied by the fins, is at least about 90% and less than about 150% of the area of the air inlet. 
     The shroud can taper inwardly toward a vertical axis. The shroud can also define a vertical axis and the heat sink can include fins that radiate from the vertical axis. The fins can include a contoured distal edge and an inner surface of the shroud can be contoured to generally follow at least one distal edge of the fins. 
     The fixture can further include a lower housing connected to the shroud. The lower housing can include openings shaped to receive associated glass panels. The openings can be in communication with the air inlet such that air from ambient entering the air inlet passes through the openings. The light fixture can further include translucent panels received in these openings. A lower most edge of the light engine can be disposed vertically above at least one of a lower most edge of the shroud or an uppermost edge of the openings in the lower housing. 
     The fixture can also include a lower housing connected to the shroud where the light source is a plurality of LEDs. The LEDs can be hidden by the shroud or the lower housing when viewed from horizontal at an elevation equal to an elevation of the LEDs. The fixture can also include a translucent cover connected to the heat sink to define a sealed cavity. The light source can be disposed in the sealed cavity. Portions of a peripheral edge of the heat sink can also be spaced from an internal surface of the shroud. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a decorative light fixture. 
         FIG. 2  is a perspective view of a light engine for the decorative light fixture of  FIG. 1 . 
         FIG. 3  is a perspective view of the light engine shown in  FIG. 2  with a translucent cover and retaining members for the translucent cover removed. 
         FIG. 4  is a side cross-sectional view taken along line  4 - 4  in  FIG. 7  (the translucent cover shown in  FIG. 4  is the same as  FIG. 2  as opposed to  FIG. 7 ). 
         FIG. 5  is a cross-sectional view shown in perspective taken along line  5 - 5  in  FIG. 7 . 
         FIG. 6  is a cross-sectional view shown in perspective taken along line  6 - 6  in  FIG. 7 . 
         FIG. 7  is a side elevation view of the light fixture shown in  FIG. 1  showing an alternative embodiment of a translucent cover for the light engine. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , a decorative light fixture  10  includes a light engine  12  disposed within a housing where the housing includes a shroud  14  and a lower housing  16  connected to the shroud. The decorative light fixture  10  can mount to a post where the light fixture illuminates a pathway, a street or another area. In this instance, the light fixture can have a similar look to decorative light fixtures that typically include a 75 watt metal-halide lamp. The light fixture can also be useful as a pendant light, where no pole is provided but instead the light fixture hangs from a bracket or other support. 
     With reference to  FIGS. 2 and 3 , the light engine  12  includes a heat sink  20  and a light source in thermal communication with the heat sink. In the depicted embodiment, the light source is a plurality of LEDs  22  mounted on a printed circuit board (“PCB”)  24  attached to a lower surface  26  of the heat sink  20 . The light engine  12  also includes reflectors  28  that redirect light emanating from the LEDs  22 . The reflectors  28  could be replaced by refractive optics to redirect light where it is desired. A translucent cover  32  attaches to the lower surface  26  of the heat sink  20  and defines a sealed cavity  34  ( FIG. 4 ) in which the electrical components of the LED light engine are housed. With reference back to  FIG. 2 , brackets  36  are used to attach the translucent cover  32  to the lower surface  26  of the heat sink  20 . The light engine  12  is more particularly described in International Application No. PCT/US2008/70184, which is incorporated by reference in its entirety. 
     LED light engines can require aggressive cooling to provide a bright long lasting light source. Where a decorative lighting fixture is desired, it can be difficult to allow for adequate air flow and adequate surface area of the heat sink to cool the LED light engine. By shaping an internal surface  38  of the shroud  14  to direct cool air over the heat sink  20 , natural convection can be used to cool the LED light engine  14  without the need for a fan or heat pipe. Additionally, the heat does not need to be conducted into a pole upon which the light fixture can be mounted. This allows the light fixture to be used as a pendant light since no pole is required for a heat sink. 
     With reference to  FIG. 4 , the decorative shroud  14  covers the light engine  12  to define an air path, designated by arrow  40 , between an air inlet  42  and an exhaust  44 . The air inlet  42  is disposed vertically below the exhaust  44 . Air moves between the air inlet and the exhaust via natural convection—fans to move the air and additional heat removal components, e.g. heat pipes, can be unnecessary. The air path is shaped to direct air over the heat sink  20  so that the air exits the shroud  14  above the light engine  12 . Both the air inlet  42  and the exhaust  44  are in communication with ambient. The shroud also defines an internal volume  46  covering the heat sink  20 . 
     The shroud  14  defines a vertical axis  50 , which is also a central axis of the light fixture  10 . In the illustrated embodiment, the shroud  14  tapers inwardly toward the vertical axis from a lower edge towards an upper end of the shroud. More particular to the embodiment that is illustrated, the shroud  14  tapers toward a cylindrical section  48  that is at the top of the shroud and concentric with the vertical central axis  50 . The cross-sectional area of the internal volume  46  taken normal to the central axis  50  adjacent the inlet  42  (see  FIG. 5 ) and not occupied by the heat sink  20  is greater than the cross-sectional area of the internal volume taken normal to the central axis adjacent the outlet. Also, cross sectional areas taken above the heat sink  20  can be less than the area of the inlet  44 . This facilitates the shroud acting as a chimney to efficiently remove heat that is generated by the LEDs  22  ( FIG. 3 ) from the light fixture. 
     With reference back to  FIGS. 2 and 3 , the heat sink  20  includes a base  52  and a plurality of spaced fins  54 . With reference to  FIGS. 4 and 6 , the fins  54  extend upwardly from the base  52  into the internal volume  46  of the shroud  14  and are arranged to be in thermal communication with the air path such that air passing through the air inlet passes through spaces between adjacent fins prior to passing through the air exhaust  44 . The fins  54  of the illustrated embodiment radiate from the central axis  50 . The fins  54  are angularly spaced from one another around the central axis  50 . With reference to  FIG. 6 , the heat sink  20  also includes a central pillar  56  that is coaxial with the central axis  50  and that extends upwardly from and normal to the base  52 . Some of the fins  54  have internal edges that are contiguous with the pillar  56  and some fins have internal edges that are radially spaced from the pillar. Many fins  54  are shown in the depicted embodiment; however, the number of fins and the surface area occupied by the fins can be dependent upon the amount of power that is to be delivered to the LEDs  22  to provide the desired light output from the light fixture. Moreover, the radial fins  54  should allow higher air velocities through the light fixture due to natural convection as compared to fins having other orientations, but the fins can be provided to have other orientations other than the radial configuration that is shown. With reference to  FIG. 4 , each fin  54  includes a contoured distal edge  58  and the inner surface  62  of the shroud  14  is contoured to generally follow the distal edges of the fins. 
     With reference to  FIG. 5 , the area of the air inlet  42  is shown which is defined by a peripheral edge  60  of the base  52  of the heat sink  20  and the internal surface  38  of the shroud  14 . Much of the peripheral edge  60  of the base  52  of the heat sink  60  is offset from the internal surface  38  of the shroud. The heat sink  20  includes extensions  62  (four extensions in the illustrated embodiment) to provide an attachment location for attaching the heat sink to the shroud  14 . 
       FIG. 5  depicts an isometric view of a cross section taken normal to the central axis  50  through the shroud  14  and the heat sink  20  at the vertical location of the air inlet  42 .  FIG. 7  shows the location of the cross section of  FIG. 5 . With reference to  FIG. 6 , the shroud  14  and the heat sink  20  define an envelope  64 , which is the internal volume  46  of the shroud  14  above the lower surface  26  of the heat sink  20  less the volume occupied by the heat sink. The cross-sectional area of the envelope  64  normal to the central axis  50  at locations above the lower surface  26  of the heat sink  20  taken through the heat sink is at least about 90% and less than about 150% of the area of the air inlet  42 . More desirably, the cross-sectional area of the envelope normal to the central axis at locations above the lower surface of the heat sink and taken through the heat sink is at least about 100% and less than about 120% of the area of the air inlet  42 . Even more desirably, the area of the exhaust  44  is about 20% to about 30% less than the area of the inlet  42 . 
     For example, the area of the air inlet  42  is shown in  FIG. 5 . With reference to  FIG. 6 , the area of the envelope  64 , which can be considered as the spaces between adjacent fins  54 , through the cross section shown in  FIG. 6  is at least about 90% of the area of the air inlet and preferably less than about 150% of the area of the air inlet. This promotes a chimney effect where the shroud  14  acts as a chimney. Where the volume of the envelope  64  between the base  52  of the heat sink  20  and an upper edge of each heat fin  54  is too small, this can restrict airflow and not allow the highest possible velocity of airflow through the fixture to cool the LEDs. Where the volume of the envelope between the base  52  of the heat sink  20  and an upper edge of each fin  54  is too large, the air velocity over the heat sink can decrease as compared to an optimally designed envelope volume. 
     With reference to  FIG. 4 , the exhaust  44  is depicted schematically. With reference to  FIG. 1 , the exhaust  44  can be formed via openings  70  formed in the shroud  14 .  FIG. 1  shows three possible locations for these openings  70 . It can be desirable to locate the openings  70  in locations that are protected from rainfall. Nevertheless, since the electrical components of the light engine  12  are disposed in a sealed cavity  34  (FIG.  4 —an electrical cable, which is not shown, passes into the sealed cavity to provide energy) the exhaust openings  70  can be located in areas where the ingress of water is possible during a rain storm. It can be desirable to have the area of the exhaust  44 , which would be the total surface area for the openings  70 , to be at least about 70% of the area of the air inlet  42 . The area of exhaust can also be less than about 80% of the area of the inlet. This promotes the chimney effect that is desirable to remove heat via convection. If the ratio of the exhaust area to the air inlet area is too large or too small, this could be detrimental to the chimney effect.  FIG. 1  simply depicts locations where the exhaust openings  70  can be located on the shroud. The number and the size of the exhaust openings will be dependent upon the area of the air inlet and the amount of power delivered to the light source of the light engine. 
     With reference back to  FIG. 1 , the lower housing  16  connects to the shroud  14  and includes openings  80  that are shaped to receive associated glass panels, which are typically found in decorative light fixtures that include an incandescent light source, a metal halide light source, or a halogen light source. This gives the decorative LED light fixture  10  the same general look as conventional light fixtures. The openings  80  can receive translucent panels  82  (only one is shown in  FIG. 1 ) or can be left open to ambient such that air entering from ambient passes through the openings prior to entering the air inlet  42 . For the embodiments that include translucent panels received in the openings  80 , holes  84  in the lower housing  16  allow for the ingress of air to cool the light engine  12 . The holes  84  shown in  FIG. 1  are simply to show possible locations for such holes. The total surface area of these holes  84  is dependent upon the flow that is desired to cool the light engine. Moreover, it can be desirable to locate these holes  84  on generally horizontal surfaces that are covered by other components of the light fixture so that the openings are protected from rain and other elements. 
     With reference to  FIG. 7 , the LEDs, which are not visible in  FIG. 7 , are hidden by the shroud  14  or the lower housing  16  when viewed from horizontal at an elevation about equal to an elevation of the LEDs. To accomplish this, the LEDs are disposed vertically above at least one of a lowermost edge  90  of the shroud  14  or an uppermost edge  92  of the openings  80  in the lower housing  16 . This obscures the point light sources from view of a person viewing the LED light fixture  10  looking downward or horizontally with respect to the light engine and the central axis  50 . This obscures the point light sources and provides for a more attractive light fixture. If desired, the translucent cover  32  can be changed from its flat configuration shown in  FIG. 1  to a hemispherical configuration shown in  FIG. 7 , but it still may be desirable to locate the LEDs so that they are hidden from view. 
     A decorative light fixture has been described with reference to the particular embodiments. Modifications and alterations will occur to those skilled in the art upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.