قابلیت انتشار

Also known as emittance

thumb|right|Blacksmiths work [[iron when it is hot enough to emit plainly visible thermal radiation.]] The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation. Thermal radiation is electromagnetic radiation that most commonly includes both visible radiation (light) and infrared radiation, which is not visible to human eyes. A portion of the thermal radiation from very hot objects (see photograph) is easily visible to the eye.