Radiative cooling

Radiative cooling is the loss of thermal energy through emitted electromagnetic radiation, usually infrared. It can cool a surface below the surrounding air when the surface radiates heat to a colder environment, especially the sky.

Thermal radiation: Electromagnetic radiation emitted by matter because of its temperature. Radiative cooling is heat loss through this broader form of energy transfer.
Radiative sky cooling: Cooling a surface by radiating heat through atmospheric spectral windows toward the cold sky. It is the central outdoor application of radiative cooling.
Emissivity: A measure of how effectively a surface emits thermal radiation compared with an ideal blackbody. High infrared emissivity helps a surface shed heat radiatively.
Evaporative cooling: Cooling caused when high-energy molecules escape from a liquid during evaporation. Unlike radiative cooling, it depends on phase change and often consumes water.
Planck's law: A law describing the spectral distribution of radiation emitted by a body in thermal equilibrium. It predicts the wavelengths and intensity of radiation available for a surface to emit.
Radiative cooling paint: A coating engineered to reflect sunlight while emitting thermal infrared radiation efficiently. Such coatings seek daytime cooling by rejecting solar heat while radiating outward.
Blackbody radiation: The electromagnetic radiation emitted by an ideal absorber and emitter in thermal equilibrium. It provides the reference spectrum for judging real cooling surfaces.
Thermoelectric cooling: Cooling produced by electric current flowing through a thermoelectric material. It requires electrical power, whereas radiative cooling can operate passively.
Atmospheric window: A wavelength range in which Earth's atmosphere absorbs relatively little incoming or outgoing radiation. Radiation escaping through this window can carry surface heat directly toward space.
Radiative cooling film: A thin engineered material that reflects sunlight and emits infrared radiation to cool underlying surfaces. Films apply spectral control to roofs, vehicles, and other exposed surfaces.

Linked from 14 pages