Patent Publication Number: US-8529097-B2

Title: Lighting system with heat distribution face plate

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH &amp; DEVELOPMENT 
     This invention was made with Government support under contract number DE FC26-08NT01579 awarded by The United States Department of Energy. The Government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates generally to lighting systems, and more particularly to lighting systems having thermal management systems. 
     High efficiency lighting systems are continually being developed to compete with traditional area lighting sources, such as incandescent or florescent lighting. While light emitting diodes (LEDs) have traditionally been implemented in signage applications, advances in LED technology have fueled interest in using such technology in general area lighting applications. LEDs and organic LEDs are solid-state semiconductor devices that convert electrical energy into light. While LEDs implement inorganic semiconductor layers to convert electrical energy into light, organic LEDs (OLEDs) implement organic semiconductor layers to convert electrical energy into light. Significant developments have been made in providing general area lighting implementing LEDs and OLEDs. 
     One potential drawback in LED applications is that during usage, a significant portion of the electricity in the LEDs is converted into heat, rather than light. If the heat is not effectively removed from an LED lighting system, the LEDs will run at high temperatures, thereby lowering the efficiency and reducing the reliability of the LED lighting system. In order to utilize LEDs in general area lighting applications where a desired brightness is required, thermal management systems to actively cool the LEDs may be considered. Providing an LED-based general area lighting system that is compact, lightweight, efficient, and bright enough for general area lighting applications is challenging. While introducing a thermal management system to control the heat generated by the LEDs may be beneficial, the thermal management system itself also introduces a number of additional design challenges. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment, a lighting system is provided. The lighting system includes a light source configured to provide area lighting and a thermal management system configured to cool the lighting system. The thermal management system comprises active and passive cooling mechanisms. The active cooling mechanisms include a plurality of synthetic jet devices. The passive cooling mechanisms include a heat distribution face plate. 
     In another embodiment, there is provided a lighting system comprising an array of light emitting diodes (LEDs) arranged on a surface of a lighting plate. The lighting system further comprises a thermal management system. The thermal management system includes a heat sink, a plurality of synthetic jets and a heat distribution face plate. The heat sink has a base and a plurality of fins extending therefrom. The plurality of synthetic jet devices are arranged to produce a jet stream between a respective pair of the plurality of fins. The heat distribution face plate is configured to transfer heat radially outward from the array of LEDs to the ambient air. 
     In another embodiment, there is provided a lighting system, comprising a light source and a heat distribution face plate. The light source comprises a plurality of illumination devices. The heat distribution face plate has an opening configured to allow the illumination devices to extend there-through. Further, the heat distribution face plate is configured to thermally conduct heat outward from the light source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is block diagram of a lighting system in accordance with an embodiment of the invention; 
         FIG. 2  illustrates a perspective view of a lighting system, in accordance with an embodiment of the invention; 
         FIG. 3  illustrates a perspective view of the light source of a lighting system, in accordance with an embodiment of the invention; 
         FIG. 4  illustrates a cross-sectional view of a portion of a thermal management system of a lighting system, in accordance with an embodiment of the invention; and 
         FIG. 5  illustrates a top view of alternative embodiments of the heat distribution face plate that may be incorporated into the light system, in accordance with embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the invention generally relate to LED-based area lighting systems. A lighting system is provided with driver electronics, LED light source and a thermal management system that provides for active and passive cooling and heat distribution in the lighting system. The thermal management system includes synthetic jet devices, a heat sink, air ports and a heat distribution face plate. The face plate is arranged in thermal contact with the LED light source to allow heat removal from the lighting system through convection and radiation cooling. The heat distribution face plate may include vents formed there-through for increased air flow when the synthetic jet devices are activated. Further, the material used to form the heat distribution face plate may be selected to increase heat transfer from the lighting source into the ambient air. In one embodiment, the lighting system fits into a standard 6″ (15.2 cm) halo and leaves approximately 0.5″ (1.3 cm) between the lamp and halo. Alternatively, the lighting system may be scaled differently, depending on the application. The presently described embodiments provide a lighting source, which produces approximately 1500 lumens (lm) with a driver electronics efficiency of 90%, and may be useful in area lighting applications. The thermal management system allows the LED junction temperatures to remain less than 100° C. for the disclosed embodiments. 
     Advantageously, in one embodiment, the lighting system uses a conventional screw-in base (i.e., Edison base) that is connected to the electrical grid. The electrical power is appropriately supplied to the thermal management system and to the light source by the same driver electronics unit. In one embodiment, the LEDs of the light source are driven at 500 mA and 59.5 V while the synthetic jet devices of the thermal management system are driven with less than 200 Hz and 120 V (peak-to-peak). The LEDs provide a total of over 1500 steady state face lumens, which is sufficient for general area lighting applications. In the illustrated embodiments described below, synthetic jet devices are provided to work in conjunction with a heat sink having a plurality of fins, air ports, and the heat distribution face plate, which may include additional air vents, to both actively and passively cool the LEDs. As will be described, the synthetic jet devices are excited with a desired power level to provide adequate cooling during illumination of the LEDs. 
     As described further below, the synthetic jet devices are arranged vertically with regard to the lighting surface. The synthetic jet devices are arranged parallel to one another and are configured to provide sufficient air flow to cool the light source. When actuated, the synthetic jet devices provide an active cooling mechanism by which ambient air is pulled through the lighting system by the synthetic jet devices through air ports and air vents, which work in conjunction to guide the air flow unidirectionally between fins of the heat sink. In addition, the heat distribution face plate provides a passive cooling mechanism. The heat distribution face plate is arranged in thermal contact with the heat sink and/or the LED base and designed to radiate heat outwardly away from the lighting system when the LED light source is illuminated. In addition, vents in the heat distribution face plate may also provide increased air flow when the synthetic jet devices are actuated. 
     Referring now to  FIG. 1 , a block diagram illustrating a lighting system  10  in accordance with embodiments of the present invention is illustrated. In one embodiment, the lighting system  10  may be a high-efficiency solid-state down-light luminaire. In general, the lighting system  10  includes a light source  12 , a thermal management system  14 , and driver electronics  16  configured to drive each of the light source  12  and the thermal management system  14 . The light source  12  includes a number of LEDs arranged to provide down-light illumination suitable for general area lighting. In one embodiment, the light source  12  may be capable of producing at least approximately 1500 face lumens at 75 μm/W, CRI &gt;80, CCT=2700 k−3200 k, 50,000 hour lifetime at a 100° C. LED junction temperature. Further, the light source  12  may include color sensing and feedback, as well as being angle control. 
     As will also be described further below, the thermal management system  14  is configured to cool the LEDs such that the LED junction temperatures remain at less than 100° C. under normal operating conditions. In one embodiment, the thermal management system  14  includes synthetic jet devices  18 , heat sinks  20 , air ports  22  and a heat distribution face plate  24 , which are configured to work in conjunction to provide the desired cooling and air exchange for the lighting system  10 . As will be described further below, the synthetic jet devices  18  are arranged to actively pull ambient air through the lighting system  10 , while the heat distribution face plate  24  is arranged to provide passive heat transfer from the light source  12  outward into the ambient air. 
     The driver electronics  16  include an LED power supply  26  and a synthetic jet power supply  28 . In accordance with one embodiment, the LED power supply  26  and the synthetic jet power supply  28  each comprise a number of chips and integrated circuits residing on the same system board, such as a printed circuit board (PCB), wherein the system board for the driver electronics  16  is configured to drive the light source  12 , as well as the thermal management system  14 . By utilizing the same system board for both the LED power supply  26  and the synthetic jet power supply  28 , the size of the lighting system  10  may be advantageously minimized. In an alternate embodiment, the LED power supply  26  and the synthetic jet power supply  28  may each be distributed on independent boards. 
     Referring now to  FIG. 2 , a perspective view of one embodiment of the lighting system  10  is illustrated. In one embodiment, the lighting system  10  includes a conventional screw-in base (Edison base)  30  that may be connected to a conventional socket that is coupled to the electrical power grid. The system components are contained within a housing structure generally referred to as a housing structure  32 . As will be described and illustrated further with regard to  FIG. 3 , the housing structure  32  is configured to support and protect the internal portion of the light source  12 , the thermal management system  14 , and the driver electronics  16 . 
     In one embodiment, the housing structure  32  includes a cage  34 , having air slots  36  there through. The cage  34  is configured to protect the electronics board having the driver electronics  16  disposed thereon. The housing structure  32  further includes a thermal management system housing  38  to protect the components of the thermal management system  14 . The cage  34  may be mechanically coupled to the thermal management system housing  38 , or some other portion of the lighting system  10 , via screws  40 . The thermal management system housing  38  many include air slots  42 . In accordance with one embodiment, the thermal management system housing  38  is shaped such that air ports  22  allow ambient air to flow in and out of the lighting system  10  by virtue of synthetic jet devices in the thermal management system  14 , as described further below with respect to  FIG. 4 . 
     Further, the housing structure  32  is coupled to a heat distribution face plate  24  configured to transfer heat from the light source  12  to the ambient air. The heat distribution face plate  24  may be made of a suitable thermally conductive plastic, metal or thermally loaded composite materials that may be loaded with metals, ceramics, etc. As will be appreciated, the heat distribution face plate  24  may be made from any thermally conductive high emissivity material that allow heat transfer from the heat source, here the light source  12 , through the material and into the air. As will be described and illustrated further below, the shape of the distribution face plate  24  is designed such that the heat from the light source  12  is transferred from inside of the lighting system  10 , outwardly toward the periphery of the heat distribution face plate  24 , such that is radiates into the air. As will be described and illustrated in  FIG. 3 , the heat distribution face plate  24  includes an opening which is sized and shaped to allow the faces of the LEDs and/or optics, of the light source  12 , to be exposed through the underside of the lighting system  10  such that when illuminated, the LEDs provide general area down-lighting. Further, as described with reference to  FIG. 4 , the heat distribution face plate  24  includes support spacers  44  configured to provide a sufficient gap between the heat distribution face plate  24  and the thermal management housing  38 , so as not to impede the air flow path through the lighting system  10  when the synthetic jet devices  18  are actuated. In alternative embodiments illustrated and described with reference to  FIG. 5 , the heat distribution face plate  24  may further include vents to increase air flow through the lighting system  10  when the synthetic jet devices  18  are actuated. 
     Turning now to  FIG. 3 , a perspective view of the lighting surface of the lighting system  10  is illustrated, in accordance with an embodiment of the invention. As illustrated, the light source  12  includes a plurality of LEDs  46 . In accordance with one embodiment, the light source  12  comprises 19 blue LEDs  46 . The LEDs  46  are arranged to protrude through an opening in the heat distribution face plate  24 . The heat distribution face plate  24  may be mechanically coupled to the lighting system  10  (e.g., to a base plate on which the LEDs  46  are arranged within the lighting system  10 ), via screws  48 . As will be described further below with respect to  FIG. 4 , the arrangement of the heat distribution face plate  24  in proximity to the light source  12  and the heat sink  20  within the lighting system  10 , allows for radial heat transfer from the light source  10  through the heat distribution face plate  24  and into the ambient air, as generally indicated by heat transfer lines  50 . In addition to the heat transfer function of the heat distribution face plate  24 , it should be noted that the heat distribution face plate  24  may also be designed to provide ornamental features that may be aesthetically pleasing to consumers. 
     Referring now to  FIG. 4 , a partial cross-sectional view of the lighting system  10  is provided to illustrate certain details of the thermal management system  18 . As previously discussed, the thermal management system  14  includes synthetic jet devices  18 , heat sink  20 , air ports  22 , and a heat distribution face plate  24 . In the illustrated embodiment, the thermal management system  14  includes a heat sink  20  having a number of fins  52  coupled to a base  54  via screws. As will be appreciated, the heat sink  20  provides a heat-conducting path for the heat produced by the LEDs  46  to be dissipated. The LEDs  46  may be mounted on an LED base plate  55  using a thermally conductive interface material (TIM). The base  54  of the heat sink  20  is arranged to rest against the backside of the light source  12  (e.g., the LED base plate  55 ), such that heat from the LEDs  46  may be transferred to the base  54  of the heat sink  20 . The fins  52  extend perpendicularly from the base  54 , and are arranged to run parallel to one another. 
     The thermal management system  14  further includes a number of synthetic jet devices  18  which are arranged adjacent to the fins  52  of the heat sink  20 . As will be appreciated, each synthetic jet device  18  is configured to provide a synthetic jet flow across the base  54  and between respective fins  58  to provide cooling of the LEDs  46 . Each synthetic jet device  18  includes a diaphragm  56  which is configured to be driven by the synthetic jet power supply  26  such that the diaphragm  56  moves rapidly back and forth within a hollow frame  58  to create an air jet through an opening in the frame  58  which will be directed through the gaps between the fins  52  of the heat sink  20 . 
     As will be appreciated, synthetic jets, such as the synthetic jet devices  18 , are zero-net-massflow devices that include a cavity or volume of air enclosed by a flexible structure and a small orifice through which air can pass. The structure is induced to deform in a periodic manner causing a corresponding suction and expulsion of the air through the orifice. The synthetic jet device  18  imparts a net positive momentum to its external fluid, here ambient air. During each cycle, this momentum is manifested as a self-convecting vortex dipole that emanates away from the jet orifice. The vortex dipole then impinges on the surface to be cooled, here the underlying light source  12 , disturbing the boundary layer and convecting the heat away from its source. Over steady state conditions, this impingement mechanism develops circulation patterns near the heated component and facilitates mixing between the hot air and ambient fluid. 
     In accordance with one embodiment, each synthetic jet devices  18  has two piezoelectric disks, excited out of phase and separated by a thin compliant wall with an orifice. This particular design has demonstrated substantial cooling enhancement, during testing. It is important to note that the synthetic jet operating conditions should be chosen to be practical within lighting applications. The piezoelectric components are similar to piezoelectric buzzer elements. The cooling performance and operating characteristics of the synthetic jet device  18  are due to the interaction between several physical domains including electromechanical coupling in the piezoelectric material used for actuation, structural dynamics for the mechanical response of the flexible disks to the piezoelectric actuation, and fluid dynamics and heat transfer for the jet of air flow. Sophisticated finite element (FE) and computational fluid dynamics (CFD) software programs are often used to simulate the coupled physics for synthetic jet design and optimization. 
     In the illustrated embodiment, each synthetic jet device  18  is positioned between the recesses provided by the gaps between the parallel fins  52 , such that the air stream created by each synthetic jet device  18  flows through the gaps between the parallel fins  52  to cool the lighting system  10 . The synthetic jet devices  18  can be powered to create a unidirectional flow of air through the heat sink  20 , between the fins  52 , such that air from the surrounding area is entrained into the duct through one of the ports  22 A and the slots  42 A on one side of the thermal management system housing  38  and warm air from the heat sink  20  is ejected into the ambient air through the other port  22 B and slots  42 B on the other side of the thermal management system housing  38 . The unidirectional airflow into the port  22 A and slots  42 A, through the fin gaps, and out the port  22 B and slots  42 B is generally indicated by airflow arrows  60 . Advantageously, the unidirectional air flow  60  prevents heat buildup within the lighting system  10 , which is a leading cause for concern in the design of thermal management of down-light systems. In alternative embodiments, the air flow created by the synthetic jet devices  18  may be radial or impinging, for instance. 
     In addition, the thermal management system  14  advantageously provides passive cooling mechanisms, as well. For instance, the base  54  of the heat sink  20  is arranged in contact with the underlying light source  12 , such that heat can be passively transferred from the LEDs  46  to the heat sink  20 . The array of synthetic jet devices  18  is arranged to actively assist in the linear transfer of heat transfer, along the fins  58  of the heat sink  20 . 
     The heat distribution face plate  24  provides yet another passive heat transfer mechanism of cooling the lighting system  10 . As illustrated, the heat distribution face plate  24  is mounted in thermal contact with the base  54  of the heat sink  20 , the LED base plate  55  and/or the thermal management system housing  38 . The heat distribution face plate  24  is thermally conductive such that heat may be transferred from the base  54  of the heat sink  20 , the LED base plate  55  and/or the thermal management system housing  38 , radially into the ambient air. Further, the support spacers  44  in the illustrated embodiment are configured to abut the thermal management system housing  38 , in such a way as to ensure sufficient air flow  60  in and out of the air ports  22 . In alternative embodiments, the support spacers  44  may be omitted and the slots  42  in the thermal management system housing  38  may be appropriately sized to provide sufficient air flow  60  in and out of the lighting system  10  to provide adequate cooling. The presently described thermal management system  14  is capable of providing an LED junction temperature of less than 100° C. at approximately 30 W of heat generation. 
     The synthetic jet devices  18  should be secured within the lighting system  10  such that they provide maximum cooling effectiveness without mechanically constraining the motion of the synthetic jet. In one embodiment, the synthetic jet devices  18  may be secured within the lighting system  10  utilizing “contact point attachment” techniques. That is, each synthetic jet device  18  is secured at multiple contact points, wherein none of the contact points is greater than 10% of the circumference of the synthetic jet device  18 . For instance, the illustrated embodiment provides that each synthetic jet device  18  is held in place by three contact points  62 . By minimizing the contact area, the synthetic jet devices are not unnecessarily restrained within the lighting system  10 . 
     In one embodiment, the thermal management system housing  38  includes molded slots within the housing structure  38  that are configured to engage the synthetic jet devices  18  at two contact points  62  (i.e., the upper two contact points of  FIG. 4 ). By providing molded slots in the thermal management system housing  38 , the synthetic jet devices  18  may be accurately positioned within the housing  38 . To further secure the synthetic jet devices  18  within the thermal management system housing  38 , a bridge  64  may be provided. The bridge  64  is configured to engage each synthetic jet device  18  at one contact point (i.e., the lower contact point of  FIG. 4 ). Accordingly, in the present embodiment, once assembled, each synthetic jet device  18  is secured within the lighting system  10  at three contact points. Additionally, a soft gel such as silicone (not shown) may be applied to each of the three contact points  62  to reduce vibrational noise and to further affix each synthetic jet device  18  within the lighting system  10 , such that the synthetic jet devices  18  do not rotate within the structure. Further, by using a mounting gel, the required holding force may be reduced. 
     As further illustrated in  FIG. 4 , the driver electronics  16  which are housed within the cage  34  include a number of integrated circuit components  64  mounted on a single board, such as a printed circuit board (PCB)  66 . As will be appreciated, the PCB  66  having components mounted thereto, such as the integrated circuit components  64 , forms a printed circuit assembly (PCA). Conveniently, the PCB  66  is sized and shaped to fit within the protective cage  34 . In accordance with the illustrated embodiment, all of the electronics configured to provide power for the light source  12 , as well as the thermal management system  14  are contained on a single PCB  66 , which is positioned above the thermal management system  14  and light source  12 . Thus, in accordance with the present design, the light source  12  and the thermal management system  14  share the same input power. 
     As previously described, various shapes and features may be incorporated into embodiments of the heat distribution face plate  24  in accordance with embodiments of the invention. Referring now to  FIG. 5 , various embodiments of the heat distribution face plate  24  are illustrated. For instance, the heat distribution face plate  24 A includes an opening  68  such that the underlying LEDs  46  (shown in  FIGS. 3 and 4 ) fit through the opening  68 . The heat distribution face plate  24 A is circular and may be substantially similar to the embodiments illustrated in  FIGS. 2-4 . The heat distribution face plate  24 B comprises a rectangular shape having two curved edges  70 . The extended rectangular shape may provide more directed thermal distribution from the LEDs  46  outward toward the curved edges  70 . In alternate embodiments, the heat distribution face plate  24  may include vents  72 . The heat distribution face plates  24 C and  24 D include vents  72 . The vents  72  may be linear segments that allow air to flow through the surface of the heat distribution face plates  24 C and  24 D. The vents  72  may improve air flow through the lighting system  10 . As will be appreciated, the angle of the vents  72  may be optimized to provide maximum air flow directly to the light source  12 . 
     Advantageously, the cooling techniques provided herein may be utilized to manufacture lighting systems with LEDs that exhibit lower the junction temperatures. The lower junction temperatures of the LEDs  46 , may enable higher drive currents to be utilized, and thus allow for the reduction in number of LEDs  46  used to produce the same lumen output as a device having a lower drive current. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. Further details regarding the driver electronics and the light source may be found in U.S. patent application Ser. No. 12/711,000, entitled LIGHTING SYSTEM WITH THERMAL MANAGEMENT SYSTEM, which was filed on Feb. 23, 2010 and is assigned to General Electric Company, and is hereby incorporated by reference herein. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.