Abstract:
An apparatus for heat dissipation for a luminaire comprises an active heat transfer device and a thermally-conductive housing. The active heat transfer device causes turbulence in an ambient fluid. The thermally-conductive housing includes a cavity and a first end. The cavity is structured for an electronic ballast of the luminaire to be housed therein and thermally attached to an interior surface of the housing to allow the housing to absorb at least a portion of heat generated by the electronic ballast. The first end is structured for the active heat transfer device to be mountable to the first end of the housing. The housing further includes at least one thermally-conductive protrusion extending from an exterior surface of the housing and exposed to the turbulence in the ambient fluid to transfer at least a portion of the heat absorbed by the housing to the ambient fluid.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application Serial No. 61/088,651, filed Aug. 13, 2008 and entitled “Turbulent Flow Cooling for Electronic Ballast,” which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     This disclosure generally relates to the field of luminaire, and more particularly to dissipation of the heat generated by ballast electronics of a luminaire. 
     2. Description of the Related Art 
     With increasing trend of energy conservation and for various other reasons, including replacement of gas-vapor lamps, solid-state lighting has become more and more popular as the source of illumination in a wide range of applications. As generally known, solid-state lighting refers to a type of lighting that emits light from a solid object, such as a block of semiconductor, rather than from a vacuum or gas tube as is the case in traditional lighting. Examples of solid-state lighting include light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), and polymer light-emitting diodes (PLEDs). Solid-state lighting as compared to traditional lighting generates visible light with reduced parasitic energy dissipation in the form of reduced heat generation. Further, solid-state lighting tends to have increased lifespan compared to traditional lighting. This is because, due to its solid-state nature, solid-state lighting provides for greater resistance to shock, vibration, and wear. 
     An LED lamp is a type of solid-state lighting that utilizes LEDs as a source of illumination, and typically has clusters of LEDs in a suitable housing. The LEDs in an LED lamp typically have very low dynamic resistance, with the same voltage drop for widely-varying currents. Thus, the LEDs cannot be connected directly to most power sources, such as the 120-volt AC mains commonly available in the U.S., without causing damages to the LEDs. Consequently, an electronic ballast is used to transform the high voltage and current from the AC mains into a typically lower voltage with a regulated current. 
     The electronic ballasts used in LED lamps have a typical conversion efficiency of 75%-95%, and more typically 85%. This means that 5% -25% of the energy used by a solid-state luminaire is wasted as heat, generated by the electronic ballast. This heat must be removed from the electronic ballast to prevent premature failure of the electronic components of the ballast. In a high-flux luminaire of, for example, 40 watts, about 8.8 watts of waste heat must be removed. However, passive cooling method using heat sink fins will not likely be able to keep temperature rise of the electronic components within safe limits if the ballast is installed in a recessed “can light” or security light type of luminaire. This is because, with such enclosed lamp mounting spaces, there is insufficient airflow to safely cool the electronic ballast. 
     There is, therefore, a need for an active cooling method and apparatus to more effectively remove the heat generated by the electronic ballast in a solid-state lighting, such as a LED lamp, to keep the temperature of the electronic components of the ballast within safe limits. 
     BRIEF SUMMARY 
     In one aspect, an apparatus for heat dissipation for a luminaire comprises an active heat transfer device and a thermally-conductive housing. The active heat transfer device causes turbulence in an ambient fluid. The thermally-conductive housing includes a cavity and a first end. The cavity is structured for an electronic ballast of the luminaire to be housed therein and thermally attached to an interior surface of the housing to allow the housing to absorb at least a portion of heat generated by the electronic ballast. The first end is structured for the active heat transfer device to be mountable to the first end of the housing. The housing further includes at least one thermally-conductive protrusion extending from an exterior surface of the housing and exposed to the turbulence in the ambient fluid to transfer at least a portion of the heat absorbed by the housing to the ambient fluid. 
     In another aspect, a device to assist active heat dissipation for a luminaire having an active cooler comprises an electronic ballast, a thermally-conductive housing, and at least one thermally-conductive protrusion extending from an outer perimeter of the housing. The thermally-conductive housing houses the electronic ballast of the luminaire therein so the electronic ballast is thermally coupled to the housing to allow at least a portion of heat generated by the electronic ballast to dissipate into the housing. The housing further includes at least one mounting structure to mount a base of the luminaire and the active cooler to the thermally-conductive housing. 
     In yet another aspect, a method of actively cooling an electronic ballast of a luminaire includes providing a thermally-conductive housing to house the electronic ballast of the luminaire therein, the housing having at least one thermally-conductive protrusion. The method also includes thermally coupling the electronic ballast to the housing to allow at least a portion of heat generated by the electronic ballast to be transferred to the housing. The method further includes causing turbulence in an ambient fluid surrounding the at least one protrusion of the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a diagram showing a luminaire enclosure device equipped with fins according to one non-limiting illustrated embodiment. 
         FIG. 2  is an assembly diagram showing an illumination device utilizing an enclosure device according to one non-limiting illustrated embodiment. 
         FIG. 3  is an assembly diagram showing a light fixture fitted with an illumination device according to one non-limiting illustrated embodiment. 
         FIG. 4A  is a diagram showing a cross-sectional view of the illumination device of  FIG. 2  according to one non-limiting illustrated embodiment. 
         FIG. 4B  is a diagram showing a cross-sectional view of the illumination device of  FIG. 2  according to another non-limiting illustrated embodiment. 
         FIG. 5  is a diagram showing turbulence in airflow created by an active heat transfer device around an enclosure device according to one non-limiting illustrated embodiment. 
     
    
    
     In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings. 
     DETAILED DESCRIPTION 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with lighting fixtures, power generation and/or power system for lighting have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments. 
     Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.” 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Further more, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The headings and Abstract of the Disclosure provided herein are for convenience only and do not interpret the scope or meaning of the embodiments. 
       FIG. 1  shows a luminaire enclosure device  10  according to one non-limiting illustrated embodiment. The enclosure device  10  comprises a housing  12  and a plurality of protrusions  14 . The housing  12  may be formed in a generally cylindrical shape, for example, with a first opening (not shown) at a first end of the housing  12  that is sized for an electronic ballast  30  of the luminaire ( FIG. 2 ) to be housed in the housing  12 . The housing  12  may have a second opening at a second end of the housing  12 , e.g., opposite the first end, that is sized to allow a base assembly  40  ( FIG. 2 ) to be mounted to the housing  12  and allow power wires  42  ( FIG. 2 ) to traverse through to provide electrical power to the electronic ballast, a light source  50  of the luminaire ( FIG. 2 ), and an active heat transfer device  20  ( FIG. 2 ). 
     In one embodiment, the plurality of protrusions  14  may be located around the outer perimeter of the housing  12  as shown in  FIG. 1 . The protrusions  14  increase the surface area of the enclosure device  10  to promote heat transfer between the enclosure device  10  and the ambient environment (e.g., air). The spacing between every two protrusions may or may not be equal to one another, and will be discussed in more detail below. In an embodiment, the plurality of protrusions  14  may be shaped as fins as shown in  FIG. 1 . It will be appreciated by those skilled in the art that, although the protrusions  14  are shown as triangular-shaped fins, the protrusions  14  may be in different shapes. In one embodiment, the protrusions  14  may be an integral part of the housing  12 . In an alternative embodiment, the protrusions  14  may be attached tightly to the outer surface of the housing  12  to ensure efficient heat transfer. The protrusions  14  add to the total surface area of the enclosure device  10 , making the enclosure device  10  a heat sink having a higher heat transfer efficiency than it would have if without the protrusions  14 . 
     In one embodiment, the enclosure device  10 , including the housing  12  and the protrusions  14 , is preferably made of thermally-conductive material such as metal, for example, aluminum, aluminum alloy, copper, copper alloy, or other suitable material having desirable thermal conductivity. With good thermal conductivity, the enclosure device  10  will be able to absorb at least a portion of the heat generated by a heat-generating component housed therein and dissipate at least a portion of the absorbed heat into the ambient environment, e.g., the ambient fluid such as air or water that surrounds the enclosure device  10 . To promote better heat transfer from the heat-generating component, e.g., the electronic ballast  30 , to the housing  12 , the heat-generating component is preferably thermally attached to the housing  12 . When the heat-generating component is thermally attached or conductively coupled to the housing  12 , heat from the heat-generating component can be transferred to the housing  12  by conduction, in addition to convection and radiation. When the heat-generating component is enclosed in housing  12  and there is not much airflow within the housing  12 , conduction is typically the most effective method of heat transfer compared to convection and radiation. 
     In one embodiment, the heat-generating component may be bonded to the housing  12  with a type of thermally-conductive adhesive  32  ( FIG. 4A ) such as, for example, the thermally-conductive epoxy TC-2810 by 3M™. In another embodiment, the heat-generating component may be mechanically secured to the housing  12  by, for example, screws and/or nuts and bolts  34  ( FIG. 4B ). In yet another embodiment, the heat-generating component may be thermally attached to the housing  12  both by bonding with thermally-conductive adhesive and by mechanical means such as screws and/or nuts and bolts or other fasteners. 
     The enclosure device  10  may, in one embodiment, further include mounting extensions  16  that protrude from the outer perimeter of the housing  12 . The mounting extensions  16  are configured for mounting another object, e.g., the active heat transfer device  20 , to the housing  12 . 
       FIG. 2  shows an assembly of an illumination device  5  utilizing the enclosure device  10  according to one non-limiting illustrated embodiment. In one embodiment, as shown in  FIG. 2 , the illumination device  5  may be a solid-state luminaire that includes the enclosure device  10 , an active heat transfer device  20 , an electronic ballast  30 , a base assembly  40 , and a solid-state lighting source  50 . In one embodiment, the solid-state lighting source  50  may comprise multiple LEDs. Electrical power may be provided to the solid-state lighting source  50  from, for example, AC power mains through the base assembly  40 , power wirings  42 , the electronic ballast  30 , and then regulated power wirings  44 . The power wirings for the active heat transfer device  20  and other components of the illumination device  5 , such as a substantially transparent cover that protects the solid-state lighting source  50  from physical damage, are not shown in order to keep  FIG. 2  uncluttered. 
     In one embodiment, the electronic ballast  30  may be housed in the enclosure device  10 , with the active heat transfer device  20  mounted to the first end of the housing  12  and the base assembly  40  mounted to the second end of the housing  12 . In other words, the electronic ballast  30  may be enclosed in the housing  12  when the illumination device  5  is assembled. Heat generated by the electronic ballast  30  may be transferred to the enclosure device  10  via conduction, convection, and radiation. In one embodiment, the electronic ballast  30  is thermally attached or coupled to the housing  12  of the enclosure device  10  as explained above to promote heat transfer from the electronic ballast  30  to the housing  12 , and subsequently to the protrusions  14 . At least a portion of the heat in the housing  12  and the protrusions  14  is then transferred to the ambient air. The rate of heat transfer from the enclosure device  10 , especially the protrusions  14 , to the ambient air can be greatly improved with the aid of the active heat transfer device  20 . 
     The active heat transfer device  20 , in one embodiment, may include a heat sink  24  and an active cooler  22 . The solid-state lighting source  50  is mounted to and in direct contact with the heat sink  24 . In an embodiment, the heat sink  24  includes multiple fins that increase surface area to enhance the transfer of heat from the heat sink  24  to the ambient air. 
     In one embodiment, the active cooler  22  may be a synthetic jet air mover and, when powered, causes ambient fluid, e.g., air, in the surrounding to circulate through the active cooler  22  and around the heat sink  24 , and thereby creating turbulent flow of cooling air over fins of the heat sink  24  as well as the protrusions  14  of the enclosure device  10 . In one embodiment, the active cooler  22  comprises a synthetic jet air mover, such as one of those manufactured by Nuventix™, which takes air in relatively slowly and ejects the same air relatively rapidly. As air moves around and past the surfaces of the heat sink  24 , thermal energy is transferred (e.g., by convection) from the heat sink  24  to the air and thereby promotes the transfer of heat away from the solid-state lighting source  50 . In another embodiment, the active cooler  22  may be a fan or other type of air mover. In an alternative embodiment, the active cooler  22  may be an active cooler that moves a fluid other than ambient air to provide cooling for the heat sink  24  and the solid-state lighting source  50 . The fluid may be, for example, water, another type of gas or liquid, or any combination thereof. 
     In one embodiment, the active cooler  22  may have multiple openings through which turbulent flow of air is ejected out. The protrusions  14  of the enclosure device  10  may be located around the outer perimeter of the housing  12  in a fashion that each protrusion  14  corresponds to and is aligned with a respective one of the openings of the active cooler  22 . Alternatively, the protrusions  14  may be located around the outer perimeter of the housing  12  in a way that the spacing between every two protrusions  14  is aligned with a respective one of the openings of the active cooler  22 . The goal may be to maximize exposure of the protrusions  14  to the turbulent airflow so that heat in the enclosure device  10  can be rapidly transferred to the ambient air to keep temperature rise in the electronic ballast  30  within safe limits. 
     In one embodiment, the solid-state lighting source  50  is mounted to one side of the heat sink  24  while the active cooler  22  is mounted to another side of the heat sink  24 . Because the solid-state lighting source  50  is at a higher temperature than the heat sink  24  when the solid-state lighting source  50  is emitting light, the resultant temperature gradient allows the heat sink  24  to absorb at least a portion of the heat generated by the solid-state lighting source  50  and thereby reduce the temperature of the solid-state lighting source  50 . However, thermal modeling has shown that without active cooling, a heat sink, such as the heat sink  24 , will not be able to keep the junction temperature of the solid-state lighting source  50  below a level sufficient to prevent a reduction of the operational life of the solid-state lighting source  50 . In other words, the heat sink  24  by itself alone can remove thermal energy from the solid-state lighting source  50  at a low rate, but it can remove thermal energy from the solid-state lighting source  50  at a higher rate when utilized with the active cooler  22  to keep the temperature of the solid-state lighting source  50  sufficiently low. 
       FIG. 3  shows a light fixture  1  fitted with the solid-state illumination device  5  according to one non-limiting illustrated embodiment. The light fixture  1  may include a lamp housing  2  attached to a luminaire mount  4 , which is used to mount the light fixture  1  to a structure such as a lamp post, wall, or the like. The lamp housing  2  may have a sensor socket  6 , where a photo detector or an activation device  60  (e.g., motion sensor) may be inserted into. The light fixture  1  additionally has a receptacle (not shown), such as a threaded socket, into which a lamp or an illumination device such as the solid-state illumination device  5  may be inserted. The solid-state illumination device  5  may be a replacement of a gas-discharge lamp that is typically used with the light fixture  1 , and is sized and shaped such that the solid-state illumination device  5  can fit inside the lamp housing  2  of the light fixture  1 . 
       FIG. 4A  shows a cross-sectional view of the solid-state illumination device  5  according to one non-limiting illustrated embodiment. As shown, the electronic ballast  30  may be thermally attached to the housing  12  by bonding with thermally-conductive adhesive  32 . 
       FIG. 4B  shows a cross-sectional view of the solid-state illumination device  5  according to another non-limiting illustrated embodiment. As shown, the electronic ballast  30  may be mechanically secured to the housing  12  by mechanical means such as screws and/or nuts and bolts  34 . It will be appreciated by those skilled in the art that, although the electronic ballast  30  is thermally attached or coupled to the housing  12  at one particular location of the housing  12  (e.g., towards the second end of the housing  12 ) as shown in  FIGS. 4A and 4B , the electronic housing  30  may alternatively be thermally attached or coupled to the housing  12  at another location within the inner perimeter of the housing  12 . It will also be appreciated by those skilled in the art that, regardless of the particular location within the enclosure device  10  at which the electronic ballast  30  is thermally attached or otherwise coupled to the housing  12 , at least a portion of the heat generated by the electronic ballast  30  will be transferred to the enclosure device  10 , and then ultimately transferred to the ambient air with the aid of the turbulent airflow generated by the active heat transfer device  20 . 
       FIG. 5  shows turbulence in airflow created by the active heat transfer device  20  around the protrusions  14  of the enclosure device  10  according to one non-limiting illustrated embodiment. It is expected that under normal conditions the ambient air is at a temperature lower than that of the electronic ballast  30  and of the enclosure device  10 , so that due to temperature gradient heat can be transferred from the electronic ballast  30  to the enclosure device  10  and to the ambient air. With the turbulent airflow over and across the protrusions  14 , heat transfer from the enclosure device  10  to the ambient air by convection should be greatly enhanced. As a result, the temperature of the electronic ballast  30  should be kept at a safe level to prevent damage to the components of the electronic ballast  30  due to excessive heating from insufficient cooling. To achieve substantial cooling, the protrusions  14  should be placed at the exact locations of the turbulent flow, for example, as shown in  FIG. 5 . 
     Thus, a luminaire enclosure device, such as the enclosure device  10 , is disclosed herein and should greatly improve upon the problems associated with insufficient cooling with passive heat sink described above. For instance, embodiments of the present invention utilize the cooling system that is typically found in solid-state luminaires, e.g., the active heat transfer device  20 , to also cool the electronic ballast  30  by providing small, thermally-conductive fins  14  at specific locations on the housing  12  where turbulent airflow is generated. By this method, heat generated in the sealed electronic ballast  30  is transferred through the wall of the enclosure device  10  and into the thermally-conductive fins  14 . 
     The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Although specific embodiments of and examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the disclosure, as will be recognized by those skilled in the relevant art. The teachings provided herein of the various embodiments can be applied to other context, not necessarily the exemplary context of solid-state luminaire generally described above. It will be understood by those skilled in the art that, although the embodiments described above and shown in the figures are generally directed to the context of solid-state lighting, luminaire utilizing traditional or other non-solid state lighting source may also benefit from the concepts described herein. For example, although the embodiments described above and shown in the figures are directed to luminaires using solid-state lighting source, the concepts and the embodiments described herein are equally applicable to luminaires other than those using solid-state lighting source. Further, although an Edison (threaded) base assembly is shown in the figures, other types of base assembly, such as a mogul base assembly, may be used. 
     All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification including, but not limited to: U.S. Provisional Patent Application Ser. No. 61/088,651, filed Aug. 13, 2008, entitled “Turbulent Flow Cooling for Electronic Ballast” and U.S. patent application Ser. No. 12/437,467, filed May 7, 2009, entitled “Gas-Discharge Lamp Replacement”, are incorporated herein by reference, in their entirety and for all purposes. Aspects of the embodiments can be modified, if necessary, to employ systems, circuits and concepts of the various patents, applications and publications to provide yet further embodiments. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.