CHAPTER 14 Thermal Considerations
14.1 Efficiency and Power Loss
People sometime refer to LEDs as being a cold light source. This is true in the sense that an element is not heated to thousands of degrees Celsius in order to produce light. However, LEDs do indeed generate heat and this has been the cause of failure of several designs. As a first approximation, the heat generated is voltage drop multiplied by current flow. A white LED with a 3.5 V drop at 350 mA will produce about 1.225 W of heat. Actually the emission of photons (light) will reduce this power a little, but it is better to design a larger heatsink to be on the safe side.
Power LEDs should always be mounted on a heatsink. For example, a traffic light using six or seven 1 W LEDs ...