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(physics) The energy-emitting propensity of a surface, usually measured at a specific wavelength.

Blacksmiths work iron when it is hot enough to emit plainly visible thermal radiation.

(physics) The energy-emitting propensity of a surface, usually measured at a specific wavelength.

Solar water heating system based on evacuated glass tube collectors. Sunlight is absorbed inside each tube by a selective surface. The surface absorbs sunlight nearly completely, but has a low thermal emissivity so that it loses very little heat. Ordinary black surfaces also absorb sunlight efficiently, but they emit thermal radiation copiously.

(physics) The energy-emitting propensity of a surface, usually measured at a specific wavelength.

Due to differences in emissivity, this infrared picture of a cold beer can shows vastly different (and incorrect) temperature values depending on the surface material. Reflections (like on the blank end of the can and the countertop) make accurate measurements of reflective surfaces impossible.