Abstract
In this study, the heat dissipation efficiencies of high power multi-chip COB (Chip-on-Board) LEDs with five different chip gaps were compared by assessing their junction temperature (Tj) and thermal resistance (Rth). Junction temperatures were measured using an IR camera and were also simulated by computational fluid dynamics (CFD) software. The effects of heat sinks with different surface areas, heat slugs made of different materials and different injection currents (different wattages) on high power LED junction temperatures are discussed. In addition, the optical characteristics of the LED, such as its lumens and luminous efficiency are evaluated. The experimental results show that a chip with a smaller gap has a higher junction temperature and more thermal resistance, and the junction temperature difference between the LEDs with the smallest and largest chip gaps is 3.12°C. Optical performance analyses show that the LED with a larger chip gap has higher lumens and higher luminous efficiency. Thus, higher junction temperatures reduce the optical performance of high power LEDs.
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