Thermal Management
LEDs, like all light sources, are not 100 percent efficient—they generate heat. This heat causes the LED chip’s temperature to rise. As the temperature rises, it can reach a point where the light conversion efficiency actually decreases as the input power is increased. Also, as the temperature rises, the long-term life of the LED decreases: the brightness of the light permanently drops.
When LEDs are used as indicators (as opposed to illuminators) the power into the device is low and the temperature rise is moderate. Lifetimes are easily 50,000 hours or above. However, LEDs used as illuminators receive large power inputs, and the heat generated must be removed from the LED chip if it is to stay efficient and have a long life.
Conductive vs. Radiant Heat Dissipation
Heat generated by an LED is quite different from the heat generated by an incandescent bulb. Because the LED heat is trapped in the chip, heat must be conducted out via a path of low heat resistance. This keeps the LED at a temperature where it will function efficiently and have a lifetime that maps to the life of the application. It will, in most cases, be necessary to remove the heat, not only from the LED chip, but also from the LED light platform, by conducting it into a heat sink. The heat sink could be the light fixture itself—an IPS pipe from the LED light to the fixture is a very good solution. The best conductor of heat is metal, so heat sinking the LED light to a large metal object delivers optimal heat conduction.
The incandescent radiates most of its heat into the surrounding air, which somewhat cools the bulb. The incandescent bulb does not conduct substantial heat into the Edison socket, which stays relatively cool.
This difference between how the two technologies dissipate their heat amounts to a sea change in the lighting business.
- Incandescent bulbs get very hot and can’t be touched without burning a finger. A bulb too close to a lampshade can start a fire or burn a dark spot on the shade.
- The actual temperature of the LED can be cool or hot depending on the specific thermal management system designed into the light. It will always be cooler to the touch than a bulb.
Existing light fixtures are not designed to manage the LED’s conductive heat dissipation. For example, there’s no easy way to get the heat out of a retrofitted LED light in a recessed ceiling fixture. Because of this, LED light wattage is severely limited (25-60 watts incandescent equivalent) when an LED light is placed in a recessed fixture.