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Li98 Thermally Conductive Adhesive Tape for LED Lighting Applications Slide 3

LEDs are cool to the touch because they generally don't produce heat in the form of infrared (IR) radiation. IR radiation heats the enclosures and surroundings of incandescent bulbs and other sources, making them hot to the touch. The absence of IR radiation allows LED fixtures to be positioned in locations where heating from conventional sources would cause a particular problem. Heat is produced within the LED device itself, due to the inefficiency of the semiconductor processes that generate light. The wall-plug efficiency of LED packages is typically in the region of 5-40%, meaning that somewhere between 60 and 95% of the input power is lost as heat. The energy consumed by a 100-watt GLS incandescent bulb produces around 12% heat, 83% IR, and only 5% visible light. In contrast, a typical LED might produce 15% visible light and 85% heat. Especially with high-power LEDs, it is essential to remove this heat through efficient thermal management. Without good heat sinking, the internal (junction) temperature of the LED rises, and this causes the LED characteristics to change. As the junction temperature of an LED is increased, both the forward voltage and the lumen output decrease. The output wavelength also shifts with a change in junction temperature. Most significantly, the junction temperature affects the lifetime of the LED. Unlike other light sources, LEDs don’t tend to fail catastrophically. Instead, the output of the LED decreases over time. The ambient temperature and the drive current both affect the junction temperature of LEDs. Other influences are the nature of the light output, whether it is steady state or pulsed, and the LED wattage per unit area of surface that dissipates heat.

PTM Published on: 2013-06-07