CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 61/663177, filed June 22, 2012, which is herein incorporated by reference in its entirety. This application is a continuation-in-part and claims priority to copending applications Attorney Docket No. 2010P25288US, U.S. Patent Application Serial No. 13/076,118, PARTIALLY RECESSED LUMINAIRE and Attorney Docket No. 2010P06973US, U.S. Patent Application Serial No. 13/076,141, PARTIALLY RECESSED LUMINAIRE, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The present disclosure relates to luminaires, and more particularly pertains to luminaires and methods for reducing the junction temperature of a light engine.

BACKGROUND

[0003] Luminaires, such as down lights or the like, may include a can and a light engine disposed within a cavity defined by the can. The light engine includes a light source configured to generate light. One such type of light source includes light emitting diodes, LEDs. While LEDs may generate less thermal energy compared to traditional bulbs (e.g., incandescent light bulbs), LEDs nevertheless generate thermal energy which should be managed in order to control the junction temperature. A higher junction temperature generally correlates to lower light output, lower luminaire efficiency, and/or reduced life expectancy. Unfortunately, managing thermal energy is particularly challenging when designing ceiling fixtures because temperature gradients in a room send the hottest air closest to the ceiling. Moreover, thermal insulation installed in the ceiling, and particularly proximate to the ceiling fixture, may reduce and/or suppresses natural convection. For example, the thermal insulation may have a thermal conductivity of approximately 0.04 W/(m-K), and as a result, the thermal insulation may generally only permit the removal of thermal energy upward from the ceiling fixture by thermal conduction which occurs at a far slower rate than thermal convection above the ceiling.

[0004] Another challenge facing the design of ceiling fixtures involves a plurality of ceiling fixtures installed throughout a room. In particular, the ceiling fixtures which are surrounded by other ceiling fixtures (e.g., ceiling fixtures in the middle of the room) are most vulnerable to overheating as they are farthest from the walls (which may help to act as a heat sink). Moreover, nearby ceiling fixtures generate thermal energy which reduces and/or minimizes any lateral temperature gradient across the ceiling. As a result, thermal energy is generally limited to upward and downward. Because hot air rises, most of the thermal energy must travel through the insulated ceiling.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Features and advantage of the claimed subject matter will be apparent from the following description of embodiments consistent therewith, which description should be considered in conjunction with the accompanying drawings, wherein:

[0006] FIG. 1 is a block diagram of one exemplary embodiment of a system consistent with the present disclosure;

[0007] FIG. 2a is a cross-sectional view of one embodiment of a luminaire consistent with the present disclosure;

[0008] FIG. 2b is a cross-sectional view of the luminaire of FIG. 2 received within a recess of a support surface consistent with the present disclosure;

[0009] FIG. 3a is a plan view of another embodiment of a PCB with the present disclosure;

[0010] FIG. 3b is a plan view of another embodiment of a PCB with the present disclosure;

[0011] FIG. 4 is a cross-sectional view of another embodiment of a luminaire consistent with the present disclosure;

[0012] FIG. 5 is a cross-sectional view of a further embodiment of a luminaire consistent with the present disclosure; and

[0013] FIG. 6 is a cross-sectional view of yet another embodiment of a luminaire consistent with the present disclosure.

DETAILED DESCRIPTION

[0014] By way of an overview, one aspect consistent with the present disclosure may feature a luminaire including a fixture, a light engine coupled to the fixture, and a heat flange configured to extend outwardly beyond the mounting surface of the luminaire. The heat flange reduces the junction temperature of the light engine by increasing the amount of convection in the surrounding air, thereby increasing the volumetric air flow across the fixture as well as the air velocity. As used herein, the term "junction temperature" is intended to refer to the maximum temperature of the light engine when operating at steady state power. In particular, thermal energy is conductively transferred from the light engine, through the fixture, to the heat flange where the thermal energy is convectively transferred from the heat flange to surrounding air to create air currents flowing along the support surface. The increased volumetric air flow and velocity transfers a greater amount of thermal energy from the fixture into the surrounding air, thereby reducing the junction temperature of the light engine. In addition, the shape of the heat flange increases the air velocity across the mounting surface of the luminaire, thereby exposing the heated air to a larger area of the mounting surface, and reducing the temperature difference needed to transfer the thermal energy from the air to the mounting surface. Reducing the junction temperature of the light engine may increase the life expectancy of the light engine and/or may allow the light engine to be operated at a higher luminance while also maintaining an acceptable service life.

[0015] Turning now to FIG. 1, one embodiment illustrating a lighting system 10 consistent with the present disclosure is generally illustrated. The lighting system 10 includes at least one partially-recessed luminaire 12 coupled, mounted, fixed, or otherwise secured to at least one mounting substrate 14a-n. For the sake of brevity, the partially-recessed luminaire 12 (also referred to simply as "luminaire") will be described as a being coupled to a ceiling 14a; however, it will be appreciated that the luminaire 12 may also be coupled to any mounting substrate 14a-n such as, but not limited to, a wall 14b, floor 14n, roof, or the like.

[0016] Referring now to FIGS. 2a and 2b, a cross-sectional view of one embodiment of a luminaire 12a for use with a ceiling 14a is generally illustrated. The luminaire 12a may be configured to be at least partially received in a recess 16 formed within the ceiling 14a, for example, as generally illustrated in FIG. 2b. The ceiling 14a may include an exterior layer 18 (for example, but not limited to, sheet rock, wood, a dropped ceiling, or the like) having a bottom surface 20, at least one stud or support 22a-n, and optionally insulation 24 (such as, but not limited to, thermal and/or sound insulation). As used herein, the exterior layer 18 and bottom surface thereof are intended to refer to the layer and surface of the ceiling 14a which are exposed to the area illuminated by the luminaire 12. Optionally, the recess 16 may include an electrical box 26 depending on the building codes. For example, the electrical box 26 may include any electrical box compatible with UL® or the like. One or more electrical wires (not shown for clarity) may be provided to supply AC and/or DC current to the luminaire 12. The recess 16 and/or electrical box 26 may have any shape such as, but not limited to, a generally square, generally rectangular, or generally circular shape.

[0017] The luminaire 12a includes a fixture 28a, a light engine 30 configured to be coupled to the fixture 28a, and a heat flange 32a configured to extend outwardly beyond the bottom surface 20 of the ceiling 14a when the luminaire is fully received in the recess as shown in FIG. 2b. The LEDs 46 may be coupled to a driver and/or control circuitry (e.g., but not limited to, a ballast, Printed Circuit Board (PCB) or the like) 48. The PCB 48 may comprise additional circuitry (not shown for clarity) including, but not limited to, resistors, capacitors, etc., which may be operatively coupled to the PCB 48 configured to drive or control (e.g., power) the LEDs 46. According to one embodiment, the PCB 48 may be housed within a flange cavity 62 of the fixture 28a.

[0018] The flange cavity 62 that the heat flange 32a creates below the ceiling 14a is used to house electronic components of, for example, the PCB 48 and/or the driver and controls components. This moves these vulnerable components from one of the hottest possible location (above the light engine) to one that is cooler and in much closer proximity to overall heat rejection of the fixture 28a. Heat sinking of, for example, the driver transistors also can be directly attached or close thermal contact with an exterior surface of the heat fiange 32a. This can be used to, for example, decrease heat on the components to prevent early failures.

[0019] Additional benefits of embodiments of the invention include EMI shielding. The heat flange 32a can provide a rim metal enclosure to act as an efficient shield to suppress any radiated EMI from, for example, LED drivers. This can be of particular importance for drivers that operate with high frequency. Embodiments of the invention can also be used to incorporate wireless dimming and controls into the fixture rim area where the driver can be positioned. The rim volume can provide both space and reduced ambient temperatures to the control components.

[0020] The fixture 28a may define a cavity 34 having a base 36, at least one sidewall 38, and an open end 40. The fixture 28a may be made from a material with a high thermal conductivity such as, but not limited to, a material having a thermal conductivity of 100 W/(m*K) or greater, for example, 200 W/(m*K) or greater. According to one embodiment, the fixture 28a may include a metal or metal alloys (such as, but not limited to, aluminum, copper, silver, gold, or the like), plastics (e.g., but not limited to, doped plastics), as well as composites. The size, shape and/or configuration (e.g., surface area) of the fixture 28a may depend upon a number of variables including, but not limited to, the maximum power rating of the light engine 30, the size/shape of the recess 16 and/or electrical box 26, and the like.

[0021] The fixture 28a may include one or more mounting devices 42a-n for securing the luminaire 12a to the recess 16 and/or electrical box 26. The mounting devices 42a-n may include one or more openings or passages 42a, b extending through the fixture 28a for receiving a fastener (such as, but not limited to, a screw, bolt, or the like, not shown for clarity) which may engage a corresponding feature of the recess 16 and/or electrical box 26 (also not shown for clarity). Alternatively (or in addition), the mounting device 42a-n may include one or more biasing devices (such as, but not limited to, biased tabs, springs, or the like 42c) configured to engage a portion of the sidewalls of the recess 16 and/or electrical box 26.

[0022] Optionally, the fixture 28a may include one or more surface layers 44 covering at least a portion of the internal surface of at least one of the base 36 and sidewall 38. The surface layers 44 may include an optical coating configured to reflect and/or direct light generated from the light engine 30 out the open end 40. For example, the optical coating may include a reflector and/or a lens configured to direct and/or focus light emitted from the light engine 30 out of the open end 40 of the luminaire 12a. Alternatively (or in addition), the surface layers 44 may include a thermal layer configured to increase the amount of thermal energy transferred from the light engine to the heat flange 32a. For example, the thermal layer may also have a high thermal conductivity, k, (e.g., but not limited to, a thermal conductivity, k, of 1.0 W/(m*K) or greater) to transfer thermal energy from the light engine 30 into the fixture 28a and to the heat flange 32a, thereby reducing the junction temperature of the light engine 30. The fixture 28a may also optionally include a lens and/or diffuser 50 extending across the open end 40 configured to diffuse the light emitted from the light engine 30.

[0023] The light engine 30 may include any light source including, but not limited to, gas discharge light sources (such as, but not limited to, high intensity discharge lamps, fluorescent lamps, low pressure sodium lamps, metal halide lamps, high pressure sodium lamps, high pressure mercury-vapor lamps, neon lamps, and/or xenon flash lamps) as well as one or more solid-state light sources (e.g., but not limited to, semiconductor light-emitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes (PLED), hereinafter collectively referred to as "LEDs 46"). The number, color, and/or arrangement of LEDs 46 may depend upon the intended application/performance of the luminaire 12a.

[0024] As discussed above, the luminaire 12a also includes a heat flange 32a coupled to the fixture 28a. The heat flange 32a may be made from a material having a high thermal conductivity (such as, but not limited to, a material having a thermal conductivity of 100 W/(m*K) or greater, for example, 200 W/(m*K) or greater) configured to transfer thermal energy away from the fixture 28a, thereby reducing the junction temperature of the LEDs 46 that make up the light engine 30. According to one embodiment, the fixture 28a may include a metal or metal alloys (such as, but not limited to, aluminum, copper, silver, gold, or the like), plastics (e.g., but not limited to, doped plastics), as well as composites. The heat flange 32a may be the same as the fixture 28a or a different material than the fixture 28a.

[0025] The heat flange 32a may include flange cavity 62 providing a hollow, generally conical frustum shape having a generally circular cross-section which generally linearly tapers radially outwardly from the distal-most end 57 towards the fixture 28a. Stated another way, the half-width r of the conical heat fiange 32a (i.e., the fiange half-width r) increases from the distal-most end 57 to proximal-most end 59 of the heat fiange 32a. As used herein, the term "generally conical frustum" is intended to mean that the top and base of the cone may be, but do not necessarily have to be, parallel to each other.

[0026] The distal-most end 57 of the heat fiange 32a also extends downwardly a depth D beyond the bottom surface 20 of the ceiling 14a. The depth D of the heat flange 32a may be selected such that the heat flange 32a has a surface area large enough to transfer enough thermal energy from the heat fiange 32 to the surrounding air by thermal convection to create an air current (as represented by arrows C) across the tapered exterior surface 60 of the heat flange 32a. The shape of the heat fiange 32a also generates air currents C that flow upwardly across the heat flange 32a and radially outwardly generally parallel to the bottom surface 20 of the ceiling 14a. Because the heated air currents C flow generally along the bottom surface 20 of the ceiling 14a, a larger area of the ceiling 14a is exposed to the heated air currents C, thereby reducing the temperature differential needed to transfer thermal energy from the heated air currents C to the ceiling 14a. The net result is that more thermal energy is transferred from the light engine 30 to the air, and ultimately to the ceiling 14a, thereby reducing the junction temperature of the light engine 30.

[0027] According to one embodiment, the heat flange 32a has a depth D equal to or greater than 0.4 times the radius R of the fixture 28a (i.e., equal to or greater than 0.2 times the diameter of the fixture 28a). For example, the depth D may be equal to or greater than 0.6 times the radius R of the fixture 28a (i.e., equal to or greater than 0.3 times the diameter of the fixture 28a); equal to or greater than 0.8 times the radius R of the fixture 28a (i.e., equal to or greater than 0.4 times the diameter of the fixture 28a); and/or equal to or greater than 1.2 times the radius R of the fixture 28a (i.e., equal to or greater than 0.6 times the diameter of the fixture 28a). Alternatively, the depth D of the heat flange 32a may be selected to be greater than or equal to 0.4R and less than or equal to 2R; greater than or equal to 0.4R and less than or equal to 1.4R; greater than or equal to 0.8R and less than or equal to 1.6R; greater than or equal to 0.8R and less than or equal to 1.4R, and/or any value in between. The conical heat flange 32a may have a maximum flange half-width r (e.g., at the proximal-most end 59 of the heat flange 32a configured to be adjacent to the ceiling 14a) equal to or greater than 0.4 times the radius R of the fixture 28a. For example, the conical heat flange 32a may have a maximum flange half-width r equal to or greater than the radius R of the fixture 28a.

[0028] The PCB and/or the driver and controls components 48 can be sized and shaped to fit within the designed flange cavity 62. The PCB 48 can also have a generally conical frustum to match the flange cavity's 62 generally conical frustum shape. As shown in FIG. 3a, the PCB 48a in a plan view has a circular with the in circular portion removed. The PCB 48a can be angled to provide a complementary generally conical frustum shape with a generally conical frustum shape that parallels the interior surface of the tapered exterior surface 60 of the flange cavity 62. Such shape can be used to maximize surface area contact with the interior surface of the tapered exterior surface 60 and minimize the thermal path to the exterior surface 60. Embodiments are not limited to a complete generally conical frustum ring. Referring to FIG. 3b, the PCB 48b can comprise multiple sections of PCB 48 that are wired together or use other methods of electronically coupling. Embodiments are not limited to a generally conical frustum shape. Referring to FIG. 4, embodiments may include a planer PCB 48 having flat circular shape or small rectangles that are positioned at relative angles to each other around the flange cavity 62. A shelf 64 that receives the PCB 48 can be constructed with additional high thermal conductivity material that is molded as a portion of the flange cavity 62 or coupled to flange cavity 62.

[0029] Referring to FIG. 5, the flange cavity 62 can incorporate phase-change material 66 within the cavity. The phase-change material 66 can be added to the flange cavity 62 adjacent or surrounding the PCB 48 to transfer the heat away and further aid in even cooling of the electronic components. Phase-change materials 66 may be waxes or paraffins with melting temperatures in the range of 60C - 90C or similar. Other materials with high latent heat of fusion can also be employed, for example certain sodium silicate materials. During the phase change process, the overall temperature can remain almost constant at the value of the melting temperature. Temperature sensors may be embedded that detect when all phase- change material 66 is molten, which will cause the temperature to rise rapidly. In this example, the temperature sensor signal can be used to reduce or turn off light output, thus protecting the fixture system from overheating.

[0030] In one example, the total power of a LED system can range from 22 watts to 30 plus watts. The PCB 48 can be generally conical frustum with a 6 to 9.5 inch hole in the middle, to fit in the flange cavity 62. When using phase-change material 66 in the flange cavity 62, the outer walls of the flange cavity 62 can run up to 1/3 of the distance from the bottom to the top of recessed LED fixture 28a. The PCB 48 and/or the driver and controls components are located in suitable groups in the triangularly shaped area/volume. The hottest components can be mounted against the tapered exterior surface 60 for optimal heat sinking. Phase- change material 66 can be placed in the flange cavity 62 on top of and around the electronic components in a similar manner as potting. The phase-change material 66 can be a wax compound with melting temperature of approximately 75 C. The amount of phase change material 66 can be selected such that the fixture can operate for 12 hours with full light output before the phase change material is melted completely. The hottest electronic components can be mounted as low as possible, to induce natural convection in the neighboring molten phase change material 66. This can further enhance heat transfer from the hottest components to the tapered exterior surface 60 and to the ambient air, reducing the temperature of the most thermally vulnerable components of the driver. The benefit can include that standard, inexpensive electronic components can be used for the driver, rather than specialized high-temperature components. A further benefit can be that the phase- change material 66 provides additional insulation of the electronic components and also prevents emission of sound from the driver components. Further, in the case of an electronic failure, the phase-change material 66 can reduce emission of smoke and sound, and reduce the associated user concern.

[0031] Embodiments are not limited to the heat flange 32a having a generally conical frustum shape. Referring to FIG. 6, the heat flange 32a can have, for example, a cylindrical shape. The heat flange 32a can have a depth D equal to or greater than 0.4 times the radius R of the fixture 28a (i.e., equal to or greater than 0.2 times the diameter of the fixture 28a). In an additional embodiment, the PCB and/or the driver and controls components 48 can be sized and shaped to fit within a flange cavity 62 that extends below the heat flange 32a. In this embodiment, the heat flange 32a can provide cooling of various other components of the system while the flange cavity 62 is isolated from the heat flow of components. The embodiment allows for direct heat flow from the PCB 48 to the air surrounding the fixture. Optionally, the embodiment can also include one or more thermal interface materials 68 disposed between the heat flange 32a and the PCB 48. The thermal interface material 68 can be used to decrease or increase the thermal resistance. In one example where sensitive electronics needs to be isolated from the heat provided by the fixture, the thermal interface material 68 can be a material the increase thermal resistance. In another example where the electronic can generate more heat than can be dissipated by the surround air, the thermal interface material 68 can be a material to decrease thermal resistance to facilitate cooling of the electronics by additional material or surface area.

[0032] The features and aspects described with reference to particular embodiments disclosed herein are susceptible to combination and/or application with various other embodiments as described in U.S. patent application 13/07614, filed March 30, 2011 and entitled "Partially Recessed Luminaire", the disclosure of which is expressly incorporated herein by reference. Such combinations and/or applications of such described features and aspects to such other embodiments are contemplated herein.

[0033] The terms "first," "second," "third," and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

[0034] While the principles of the present disclosure have been described herein, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation as to the scope of the invention. The features and aspects described with reference to particular embodiments disclosed herein are susceptible to combination and/or application with various other embodiments described herein. Such combinations and/or applications of such described features and aspects to such other embodiments are contemplated herein. Other embodiments are contemplated within the scope of the present invention in addition to the exemplary embodiments shown and described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the following claims.