Semiconductor light sources, such as LEDs, have been employed in automotive warning lamps and the like for some time now. When operated properly, the reliability and efficiency of LED light sources provides significant advantages over conventional incandescent bulbs and the like.
More recently, with improvements in the output of the semiconductor light sources, it has become possible to construct headlamps and other higher output automotive lighting systems with relatively high output LED light sources. However, even with the most recently developed LED light sources, the amount of light emitted by these sources is relatively low and care must be taken to not obscure or otherwise render a significant portion of the emitted light unused.
Further, to obtain the desired level of lumens, these LED light sources are typically operated at the upper end of their performance envelopes. As is well known, semiconductor junctions such as those in LEDs are susceptible to heat. Specifically, the efficiency of an LED decreases as the temperature of its semiconductor junction increases and the lifetime of the LED decreases when it is operated at higher semiconductor junction temperatures compared to its lifetime when operated at lower junction temperatures. These problems are exacerbated with high output LEDs which generate proportionally greater amounts of heat than LEDs with lower outputs, especially when such LED light sources are operated at the upper end of their performance envelopes.
Many different approaches are known to remove heat from LEDs. U.S. Pat. No. 5,751,327 to De Cock et al. shows an LED printer head which includes a water cooled carrier to which the LEDs are mounted. U.S. Pat. No. 6,113,212 to NG shows a similar system for use in color copiers. U.S. Pat. No. 6,220,722 shows an LED bulb which includes multiple LED light sources mounted to a substrate which is, in turn, connected to a column which includes a forced air cooling system. U.S. Pat. No. 6,375,340 to Biebl et al. shows a multi-LED array wherein the LEDs are mounted on a plate of a ceramic substrate which dissipates the heat produced by the elements. U.S. Pat. No. 6,452,217 to Wojnarowski et al. shows an LED flashlight wherein a phase change material is employed to remove heat from LED light sources. U.S. Pat. No. 6,481,874 to Petroski shows an LED lighting system wherein the LED die is thermally connected to a large heat sink. U.S. Pat. No. 6,573,536 shows an LED light system wherein the LEDs are mounted on a hollow tubular mount through which a cooling fluid flows.
While these solutions may be acceptable in many environments, in the environment of higher output automotive lighting systems, such as headlamps, none of these solutions is practical as they either do not readily permit the LED sources to be positioned, as needed, with respect to reflectors and/or lenses, or they are not capable of reliably removing enough heat from closely grouped LED light elements which can be exposed to the wide range of expected ambient temperatures and operating conditions typical for automotive systems.