Compact Led Downlight with cuspated flux-redistribution lens
This application claims benefit of U.S. Provisional Applications Nos. 61/195,290 filed Oct. 6, 2008, and 61/273,321 filed Aug. 3, 2009, which are incorporated herein by reference in their entirety. Reference is also made to U.S. patent application Ser. No. 12/387,341 titled “Remote-Phosphor LED Downlight,” filed May 1, 2009 by the same inventors, which is incorporated herein by reference in its entirety, and to U.S. Provisional Application No. 61/205,390, filed Jan. 16, 2009 by Falicoff and Sun, which is incorporated herein by reference in its entirety.
Downlights are lighting fixtures typically mounted in ceilings for illumination directly below them. Conventionally, these ubiquitous luminaires generally comprise an incandescent spotlight mounted within a can. Since incandescent bulbs operate hot anyway, they are not thermally bothered by the can being a trap for hot air. It would be highly desirable to replace incandescent light bulbs with lamps using light-emitting diodes (LEDs), because LEDs last much longer and use much less electricity than incandescent bulbs. However, even LEDs produce a significant amount of heat (about 3/4 of their electrical power consumption) and LEDs are temperature-vulnerable, so that downlights are a more difficult lighting application than anticipated. This is because the optics of a conventional downlight dictate that the actual light source be installed at the top of the can, facing downwards. The waste heat of the LEDs cannot very effectively be dissipated passively into the stagnant hot air of the typical downlight can. This poor heat dissipation typically limits the total electrical power that can be handled in a solid state LED downlight to a maximum of approximately 5 watts.
An LED downlight, comprising:a primary reflector having an upper end and an open lower end;an LED printed circuit board assembly disposed in said upper end of said reflector;an optical assembly positioned beneath said LED printed circuit board assembly;a secondary reflective ring positioned beneath said LED printed circuit board assembly and within said primary reflector housing, said secondary reflector ring supporting said optical assembly and improving light distribution.
This power limit can only be overcome if the can is dramatically increased in size to aid in heat management, or if active cooling or ventilation is provided, a severe limitation. Furthermore, the best commercially available 5 watt LED sources have an efficacy of 60 lumens per Watt (LPW), including driver losses. This limits such a solid-state downlight to a flux of approximately 300 lumens. It would be desirable to have a standard size solid state downlight producing 600 to 1000 lumens. That light output is achievable only if the heat management can handle a minimum of 10 watts, which mandates moving the LEDs down from the top of the can.
This power limit can only be overcome if the can is dramatically increased in size to aid in heat management, or if active cooling or ventilation is provided, a severe limitation. Furthermore, the best commercially available 5 watt LED sources have an efficacy of 60 lumens per Watt (LPW), including driver losses. This limits such a solid-state downlight to a flux of approximately 300 lumens. It would be desirable to have a standard size solid state downlight producing 600 to 1000 lumens. That light output is achievable only if the heat management can handle a minimum of 10 watts, which mandates moving the LEDs down from the top of the can.
Embodiments of the present invention provide a reflector-dish LED downlight with a novel type of lens positioned over the light source and optically coupled to it so that a full hemispheric distribution is obtained within the lens. The lens profile has a central cusp that receives upward-going light and deflects it outwards, allowing the reflector dish to have a central hole that will act as a chimney to promote air circulation around the heat sink.
The lens profile of one preferred embodiment will also deflect light below horizontal so that the reflector dish becomes deep enough to entirely enclose the light source. Because the reflector dish divides the interior of the can, air is able to circulate upwards inside the dish and downwards outside the dish but inside the can. The above-discussed problem of hot air being trapped within the can when the can and dish both extend downwards below the light engine may consequently be greatly mitigated. Alternatively, the lens deflects at the center, graduating to zero deflection horizontally, so the reflector profile does not extend below the source. In addition, the same lens can be used with different reflector dishes in order to generate different sized illuminated circles on the target plane. The exact shape of the dish will also determine the distribution of illumination, whether uniform, centrally peaked, or centrally darkened.
An LED downlight comprises a primary reflector having an upper end and a lower open end, a LED printed circuit board assembly disposed near the upper end of the primary reflector, a mixing subassembly depending downwardly toward a lens, the mixing subassembly receiving light from the LED printed circuit board assembly, the lens beneath the LED printed circuit board assembly, a retaining ring receiving the lens, the retaining ring disposed within the primary reflector, the retaining ring further comprising an angled inner surface. The LED downlight further comprising a plurality of LED apertures disposed in an upper surface of the mixing subassembly. The LED downlight further comprising the mixing subassembly having a reflective inner surface. The LED downlight wherein the mixing assembly is substantially frusto-conical in shape. The LED downlight further comprising a mixing chamber being seated in the retaining ring. The LED downlight wherein the mixing chamber is fastened to the heat sink.
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