Patent Application
20110242828
The application relates generally to light-emitting diode (LED)-based technology lighting systems, and more particularly, to lighting assemblies or lighting fixtures having controlled directional heat transfer.
Lighting systems utilizing LEDs are widely used in various applications including, but not limited to, hazardous area lighting, general indoor and outdoor lighting, and backlighting. Lighting systems utilizing LEDs are a longer lasting, more efficient alternative to using lighting systems utilizing conventional light sources such as incandescent lamps and fluorescent light sources. However, the implementation of LED-based lighting systems has been hindered by the amount of heat build-up within the lighting assembly. Heat build-up within the lighting assembly can reduce light output of the LEDs and shorten the lifespan of the LEDs, thus potentially causing the LEDs to fail prematurely.
Heat sinks are typically used in LED-based lighting systems. The heat sinks provide a pathway for absorbing the heat generated from LEDs in the lighting assembly, and for dissipating the heat directly or radiantly to the surrounding environment. However, conventional LED-based lighting systems employing heat sinks typically have poor heat transfer between the LEDs and the heat sink, and/or the heat drawn away from the LEDs is transferred to other heat sensitive components, such as drivers in the assembly.
Therefore, a need exists in the art for lighting assemblies having controlled directional heat transfer.
The present invention satisfies the above-described need by providing a LED-based lighting system having capabilities for controlled heat transfer from a light source assembly to an exterior of a lighting fixture, while minimizing transfer of heat to components within a driver housing.
In one aspect, a lighting fixture having controlled directional heat transfer can include a light source assembly, a heat sink, a conductive sealing member, such as a thermal gasket, positioned between the heat sink and the light source assembly, and a driver housing for containing components for controlling the lighting fixture. The conductive sealing member generally has a thermal conductivity of at least about 6 Watts per meter-Kelvin (W/mK), and/or a thermal impedance of less than about 0.21 degree-C. inch squared per Watt (° C.-in2/W). The light source assembly can include an array of LEDs. The heat sink can include fins extending from a central housing of the heat sink. A nonconductive or semi-conductive sealing member, such as a silicone gasket, can be positioned between the heat sink and the driver housing so as to minimize the amount of heat transferred from the heat sink to the driver housing. Alternatively, a conduit can be to the driver housing and the heat sink to provide a gap between the driver housing and the heat sink. The conduit provides a passageway from an interior of the heat sink to an interior of the driver housing. The driver housing can be positioned at a location remote from the light source assembly and the heat sink, and be electrically coupled to the light source assembly by wiring.
In another aspect, a lighting assembly is defined that includes a light source assembly, a heat sink, and a conductive sealing member positioned between the heat sink and the light source assembly. The conductive sealing member can be a thermal gasket.
In yet another aspect, a lighting fixture is defined that includes a light source assembly, a heat sink, a gear module for containing components for controlling the lighting fixture, and a thermal gasket between the heat sink and the light source assembly. The thermal gasket generally has a thermal conductivity of at least about 6 W/mK, and/or a thermal impedance of less than about 0.21° C.-in2/W. The lighting fixture can include a nonconductive or a semi-conductive sealing member, such as a silicone gasket, positioned between the heat sink and the gear module. Alternatively, the lighting fixture can include a spacer that provides a gap between the gear module and the heat sink. The gear module can also be remotely located from the light source assembly and the heat sink.
The present invention provides LED-based technology lighting systems having controlled directional heat transfer capabilities. The lighting systems generally include an LED light source assembly, a heat sink, a conductive sealing member positioned between the LED assembly and the heat sink, and a driver housing. Generally, the conductive sealing member has a thermal conductivity of at least about 6 W/mK, a thermal impedance of less than about 0.21° C.-in2/W, and/or can operate in a temperature range of from about −45° C. to about 200° C. without breaking down. In certain exemplary embodiments, the lighting systems also include a nonconductive or a semi-conductive sealing member positioned between the heat sink and the driver housing. In certain alternative exemplary embodiments, the lighting systems include a gap between the heat sink and the driver housing. The lighting systems can effectively reduce the surface temperature of the light source assembly, and improve the performance of the lighting system through controlled thermal management.
The invention may be better understood by reading the following description of non-limitative, exemplary embodiments with reference to the attached drawings wherein like parts of each of the figures are identified by the same reference characters.
The heat sink 104 includes a central housing 104c (
In certain exemplary embodiments, each of the fins 120 are equal in size. In other embodiments, the fins 120 may have different sizes. In certain other embodiments, the fins 120 may extend horizontally outward from the housing 104c. One having ordinary skill in the art will recognize that the fins 120 can be sized and oriented any number of ways on the heat sink 104. A bottom end 104b of the heat sink 104 is coupled to a top end 106a of the LED assembly 106. The LED assembly 106 is configured to house at least one LED (not shown) thereon. In certain exemplary embodiments, the fins 120 are flush with or recessed from an exterior of the driver housing 102 and/or from an exterior of the LED assembly 106.
The semi-conductive sealing member 130 is positioned between the lower portion 112 of the driver housing 102 and the top end 104a of the heat sink 104. In certain alternative embodiments, the semi-conductive sealing member 130 is replaced with a nonconductive sealing member. In certain exemplary embodiments, the semi-conductive sealing member 130, the driver housing 102, and the heat sink 104 are coupled together using fastening devices, such as screws (not shown). In certain exemplary embodiments, the screws are nonconductive. In certain alternative embodiments, the screws are conductive. In certain embodiments, the semi-conductive sealing member 130, the driver housing 102, and the heat sink 104 are coupled together by clamping of the driver housing 102 to the heat sink 104. In certain embodiments, a nonconductive epoxy may be used to permanently attach the heat sink 104 to the driver housing 102, and the sealing member 130 would be removed. The semi-conductive sealing member 130 provides an environmental seal between the driver housing 102 and the heat sink 104 so as to protect the components within the driver housing 102 from direct exposure to a hazardous environment. In certain exemplary embodiments, the semi-conductive sealing member 130 is a silicone gasket. In certain embodiments, the semi-conductive sealing member 130 is a gasket constructed of polychloroprene, such as Neoprene™ rubber, a fiber gasket, or a gasket constructed of polytetrafluoroethylene (PTFE), such as Teflon™ material.
The conductive sealing member 140 is positioned between the bottom end 104b of the heat sink 104 and the top end 106a of the LED assembly 106, and is aligned with a perimeter of the bottom end 104b of the heat sink 104. In certain exemplary embodiments, the top end 106a of the LED assembly 106 includes an outer lip 106c that surrounds the bottom end 104b of the heat sink 104 when coupled together. The lip 106c functions to create a labyrinth seal, which increases the resistance to water ingress. The lip 106c can also assist in the assembly of the heat sink 104 to the LED assembly 106. In certain exemplary embodiments, the conductive sealing member 140, the heat sink 104, and the LED assembly 106 are coupled together using fastening devices (not shown). In certain exemplary embodiments, the fastening devices are conductive screws. In certain alternative embodiments, the conductive sealing member 140, the heat sink 104, and the LED assembly 106 are coupled together using adhesives. The conductive sealing member 140 provides a seal between the heat sink 104 and the LED assembly 106 so as to protect the LEDs and components within the LED assembly 106 from moisture and dust, as well as from direct exposure to a hazardous environment. In certain exemplary embodiments, the conductive sealing member 140 is a thermal gasket. In certain exemplary embodiments, the conductive sealing member 140 is fabricated from a boron nitride filled silicone elastomer, with or without fiberglass reinforcement. In certain exemplary embodiments, the conductive sealing member 140 is a crushed copper gasket. In certain exemplary embodiments, the conductive sealing member 140 has a conductivity of greater than about 6.0 W/mK, and maintains an environmental sealing. Generally, the conductive sealing member 140 has a greater conductivity, and is not as easily effected by temperatures and corrosive atmospheres as other thermal sealing members, such as thermal grease and thermal tape, would be. In certain exemplary embodiments, the conductive sealing member 140 has a thermal impedance of less than about 0.21° C.-in2/W. In certain exemplary embodiments, the conductive sealing member 140 has a thickness of at least about 0.020 inch (in). In certain exemplary embodiments, the conductive sealing member 140 can operate in a temperature range of from about −45° C. to about 200° C. without breaking down.
The lens 150 is positioned at or within a bottom end 106b of the LED assembly 106. Light produced from the LEDs (not shown) that are mounted on the LED assembly 106 can pass through the lens 150 to illuminate an area. The lens 150 can be a clear polyvinyl cover or a glass window that protects the LEDs from direct exposure to a hazardous environment. In certain embodiments, the lens 150 sealingly engages the LED assembly 106 via an o-ring 152.
The LEDs emit heat when operating. Because of the high thermal conductivity of the conductive sealing member 140, the heat is actively transferred from the LED assembly 106 to the heat sink 104 through the conductive sealing member 140, thereby reducing the overall temperature within the LED assembly 106 and protecting the LEDs from potentially damaging heat. The presence of the nonconductive or semi-conductive sealing member 130 minimizes or eliminates heat transfer from the heat sink 104 to the driver housing 102, and thus, the heat is dissipated primarily through the fins 120 to the surrounding environment. Therefore, the components housed within the driver housing 102 are protected from exposure to potentially damaging heat. The presence of the nonconductive or semi-conductive sealing member 130 can also protect the interior from moisture and dust ingress.
The conductive sealing member 240 is similar to the conductive sealing member 240, the difference being in the physical structure. The conductive sealing member 240 is positioned between the bottom end 204b of the heat sink 204 and the top end 206a of the light source assembly 206. In certain exemplary embodiments, the bottom end 204b of the heat sink 204 has a circular-shaped perimeter. The conductive sealing member 240 also has a circular shape corresponding to the shape of the bottom end 204b of the heat sink 104. Similarly, the top end 206a of the light source assembly 206 has a shape corresponding to the conductive sealing member 240. One having ordinary skill in the art will recognize that the bottom end 204b of the heat sink 204 can have any closed circuit shape however, and the conductive sealing member 240 and the top end 206a of the light source assembly 206 will have a corresponding shape. In certain exemplary embodiments, the conductive sealing member 240, the heat sink 204, and the light source assembly 206 are coupled together using fastening devices (not shown). In certain exemplary embodiments, the fastening devices are conductive screws. In certain other embodiments, the heat sink 204 and the light source assembly 206 are coupled together by clamping, threading, or a quarter turn with locking feature. The conductive sealing member 240 provides a seal between the heat sink 204 and the light source assembly 206 so as to protect the light source and components within the light source assembly 206 from direct exposure to a hazardous environment. In certain exemplary embodiments, the conductive sealing member 240 is fabricated from a boron nitride filled silicone elastomer, with or without fiberglass reinforcement. In certain exemplary embodiments, the conductive sealing member 240 is a crushed copper gasket. In certain exemplary embodiments, the conductive sealing member 240 has has a conductivity of greater than about 6.0 W/mK, and maintains an environmental sealing. Generally, the conductive sealing member 240 has a greater conductivity, and is not as easily effected by temperatures and corrosive atmospheres as other thermal sealing members, such as thermal grease and thermal tape, would be. In certain exemplary embodiments, the conductive sealing member 240 has a thermal impedance of less than about 0.21° C.-in2/W. In certain exemplary embodiments, the conductive sealing member 240 has a thickness of at least about 0.020 in. In certain exemplary embodiments, the conductive sealing member 240 can operate in a temperature range of from about −45° C. to about 200° C. without breaking down.
The lens 250 is positioned at or within a bottom end 206b of the light source assembly 206. Light produced from the light source (not shown) that is/are mounted on the light source assembly 206 can pass through the lens 250 to illuminate an area. The lens 250 can be a clear polyvinyl cover or a glass window that protects the LEDs from direct exposure to the hazardous environment. In certain embodiments, the lens 250 sealingly engages the light source assembly 206 via an o-ring (not shown).
The light source emits heat when operating. Because of the high thermal conductivity of the conductive sealing member 240, the heat is actively transferred from the light source assembly 206 to the heat sink 204 through the conductive sealing member 240, thereby reducing the overall temperature within the light source assembly 206 and protecting the light source from potentially damaging heat. Heat is transferred from the heat sink 204 to the exterior of the lighting system 200 via the fins 220 and the top end 204a of the heat sink 204. The presence of the gap 230 substantially reduces and/or may eliminate the amount of heat transferring from the heat sink 204 to the gear module 202. Therefore, the components housed within the gear module 202 are protected from exposure to potentially damaging heat.
The lighting systems of the present invention demonstrate inherent safety qualities by thermal management. To facilitate a better understanding of the present invention, the following examples of preferred embodiments are given. In no way should the following examples be read to limit or define the scope of the invention.
A lighting fixture of the present invention was subjected to Cycling Rain and Dielectric Withstand testing per UL1598 section 16.5.2 and 17.1 (dated Sep. 17, 2008). The lighting fixture included a thermal gasket positioned between a heat sink and a LED assembly, and a silicone gasket positioned between a driver housing and the heat sink, as shown and described with respect to
The interior of the lighting fixture was powdered, and the lighting fixture was assembled to a JM5 stanchion mount and vented. For the Cycling Rain test, three rain heads were positioned about 60 inches from the lighting fixture. The lighting fixture was operated for one hour. After one hour, the LEDs were turn off, and water was sprayed from the rain heads at a pressure 5 pounds per square inch (psi) onto the lighting fixture. After one-half hour, the LEDs were turned on again and water continued to spray on the lighting fixture for two hours. Finally, the LEDs were turned off and water continued to spray on the lighting fixture for an additional one-half hour. At the conclusion of the test, the lighting fixture was examined and no water was observed on the powdered interior of the lighting fixture.
For the Dielectric Withstand test, the LEDs were disconnected from the lighting fixture. The ambient temperature was 22 degrees Celsius and the relative humidity was at 35 percent. A Hi-pot Tester, model number 230425, commercially available from Biddle, applied a voltage of 1480 VAC to the lighting fixture for one minute. The lighting fixture was examined for arcing to determine if any breakdown had occurred. Electrical continuity was found between all of the components in the lighting fixture, and no breakdown of any components was observed.
The environmental sealing effect of the presence of a thermal gasket in a lighting fixture of the present invention was tested. A lighting fixture including a thermal gasket positioned between a heat sink and a LED assembly, and a silicone gasket positioned between a driver housing and the heat sink, as shown and described with respect to
The test was repeated on a similar lighting fixture, but with the thermal gasket removed. The interior of the lighting fixture was powdered, and the lighting fixture was assembled to a JM5 stanchion mount and vented. A one inch diameter nozzle was positioned about 10 feet from the lighting fixture. A stream of water was directed at the lighting fixture for a duration of five minutes at 15 psi and 110 gallons per minute (gpm). At the conclusion of the test, the lighting fixture was examined, and water was observed to have entered the lighting fixture between the heat sink and the LED assembly. Approximately 300 milliliters (mL) was measured to enter the lighting fixture.
Therefore, the presence of a thermal gasket in the lighting fixture was shown to provide an environmental seal between the heat sink and the LED assembly.
Temperature tests were performed on a lighting fixture to determine the temperature differences of the fixture components using (i) no gasket, (ii) a silicone gasket, and (iii) a thermal gasket positioned between a heat sink and a LED assembly of the lighting fixture. Each of the lighting fixtures included two LED drivers (EWC-050S119SS-0021, 50W, input voltage/current 100-240 VAC/0.7 A, 50/60 Hz, output voltage/current 21-42 VDC/1.19 A, UL, CSA, CE, IP67) commercially available from Inventronics, six LED arrays (BXRA-C1200, cool white) commercially available from Bridgelux, and a ceiling mount cover (catalog number CM2) commercially available from Cooper Crouse-Hinds.
A lighting fixture having a thermal gasket, series 220 MS2423 commercially available from Thermagon, between the heat sink and the LED assembly was mounted in a room with provisions for maintaining a constant ambient temperature. The thermal gasket had a thermal conductivity of 6 W/mK and a thermal impedance of 0.21° C.-in2/W. The silicone gasket had a thermal conductivity of 0.22 W/mK. The lighting fixture was tested in environments having ambient temperatures of (i) 25 degrees Celsius, (ii) 40 degrees Celsius, and (iii) 55 degrees Celsius. Thermocouples (TC) were positioned at the following locations on the lighting fixture: (i) adjacent a first LED, (ii) adjacent a second LED, (iii) on one driver, (iv) on the other driver, (v) the interior of the LED assembly, (vi) the exterior of the LED assembly, (vii) the upper portion of a fin on the heat sink, (viii) the lower portion of a fin on the heat sink, (ix) at the silicone gasket above the heat sink, (x) at the lens gasket, (xi) on the lens, and (xii) on another part of the lens. The lighting fixture was subjected to 240 V, 90 W, 0.46 A, and the maximum temperatures from each thermocouple were recorded after the temperatures stabilized. The tests were repeated for a lighting fixture having no gasket between the heat sink and the LED assembly, and a lighting fixture having a silicone gasket, model MS1405 commercially available from Higbee, between the heat sink and the LED assembly. Results from the Temperature tests are shown in Table I below.
Therefore, the presence of a thermal gasket in the lighting fixture was shown to provide an environmental seal between the heat sink and the LED assembly, and effectively draw heat away from the LED assembly.
Vibration tests were performed on lighting fixtures of the present invention to determine if the components within the lighting fixtures could withstand vibrations. Each of the lighting fixtures tested included a thermal gasket positioned between a heat sink and a LED assembly, a silicone gasket positioned between a driver housing and the heat sink, as shown and described with respect to
Accordingly, the above examples demonstrate that the lighting fixtures of the present invention are able to effectively control the direction of heat transfer, while being suitable for use in hazardous areas.
Therefore, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned as well as those which are inherent therein. While the invention has been depicted and described by reference to embodiments of the invention, such a reference does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alternation, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent arts and having the benefit of this disclosure. The depicted and described embodiments of the invention are exemplary only, and are not exhaustive of the scope of the invention. Consequently, the invention is intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects.
