It is a common misunderstanding that LEDs produce trivial heat. In fact, they produce quite a bit of heat per lumen. The primary reasons for the misunderstanding are:
1) This heat is emitted to the rear of the junction, not "out the front" in the same direction as the light as is the case with most other light sources, and 2) Most people's only LED experience is with the very small, relatively low output items used as indicator lights on e.g. electronic equipment and dashboards. A great deal more light is required for illumination than for indication.The backside heat produced by LEDs powerful and numerous enough for illumination is *not* trivial, and it creates two problems: There is the issue of thermal resistance in the materials used to build the lighting device, its housing and surroundings -- this doesn't really differ from the same problem with any other light source, with the exception of the location/direction of the heat. This is throwing obstacles into the development, for instance, of LED vehicle headlamps. Not only is the significant backside heat creating thermal management problems requiring elaborate and expensive solutions (fan-cooled headlamps!) to avoid exceeding temperature limits in the lamp housings themselves, but the lack of
*frontside* heat means the lens doesn't defog or thaw when the lamp is turned on. Too much heat in back, not enough in front!LEDs are also highly temperature sensitive with respect to their output. It's common to see a swing on the order of +60% at -30°C to -40% at
+40°C, relative to nominal output at 20°C. Most other light sources in current use are minimally temperature sensitive in this manner, if at all. Filament and arc lights generally don't know or care what the ambient temperature is. Fluorescent lamps tend to have low output at low temperatures (and unreliable starting, in extremely low temperatures), but their internal heat tends to counteract low ambients such that this tendency amounts to little more than extended ramp-up time when started from cold. While thermal direction and management issues are causing problems for headlamp engineers, the temperature sensitivity of LEDs' output makes problems at the other end of the vehicle: How do you design a brake lamp that is guaranteed to be sufficiently intense at 40°C when its emitters are producing only 60% of their rated output, while not being overly intense at -40°C when the emitters are producing 160% of their rated output? It's not as easy as it sounds.Unfortunately, it really is your only reliable option.
DS