Thermal radiation emmitted by a surface of a material.
An electromagnetic radiation that may include both visible radiation (light) and infrared radiation, which is not visible to human eyes.
Emissivities are important in several contexts:
- Insulated windows – Warm surfaces are usually cooled directly by air, but they also cool themselves by emitting thermal radiation.
- emissivity coatings emit less thermal radiation than ordinary windows. In winter, these coatings can halve the rate at which a window loses heat compared to an uncoated glass window.
- Temperature measurements – Pyrometers and infrared cameras are instruments used to measure the temperature of an object by using its thermal radiation; no actual contact with the object is needed. The calibration of these instruments involves the emissivity of the surface that’s being measured.