Thermal radiation is electromagnetic radiation from an object that is simply caused by its temperature. It rapidly increases in power, and also increases in frequency, with increasing temperature.

A black body is an object that absorbs all electromagnetic radiation that falls onto it. For this case there are formulas for the power as a function of temperature, etc.

A device specially made for thermal radiation may have different purposes:

• the radiation itself may be the objective, as in a light bulb
• the objective may be cooling

For example, spacecraft may have thermal radiators, also called heat radiators to lose excess heat. They tend to be reflective to avoid absorption of solar radiation energy. E.g. the Space Shuttle has heat radiators mounted on the inner surfaces of the payload bay doors, and so are kept open while the Shuttle is in orbit.