The introduction of high brightness light emitting diodes (LEDs) with white light and monochromatic colors has allowed LED penetration into general illumination applications. The increased electrical currents used to drive these LEDs have resulted in high heat fluxes, often exceeding those for average silicon computer chips. The output of a typical HB LED is today over 100 lumens, achieved with heat fluxes in excess of 300 W/cm2. Thermal management is, thus, a critical technology for LED lighting. Much of the current LED thermal research and development is focusing on air cooling with heat sinks. While these approaches provide significant heat removal capability, they are constrained by the presence of multiple interface resistances and they cannot effectively address non-uniform chip temperatures and local phosphor hot spots. To overcome the limitations imposed by air cooling, this research will investigate the potential of direct liquid cooling to provide an additional thermal path for heat dissipated in the LEDs and phosphor layers. The introduction of topside liquid cooling with optically-transparent liquids is expected to dramatically reduce average chip temperatures and to improve the uniformity of chip and phosphor temperature, leading to higher light extraction efficiencies.
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