nonblackbody

A nonblackbody is an object that does not absorb all incident electromagnetic radiation. Unlike a blackbody, which has an absorptivity of 1 at all wavelengths, a nonblackbody reflects or transmits some portion of the radiation that strikes it. The absorptivity of a nonblackbody is wavelength-dependent and is always less than 1.

The spectral radiance of a nonblackbody differs from that of a blackbody at the same temperature. While a blackbody's spectral radiance is described by Planck's law, the radiance of a nonblackbody is modified by its emissivity, which is equal to its absorptivity at thermal equilibrium. Therefore, the spectral radiance of a nonblackbody is the product of its emissivity at a given wavelength and the blackbody spectral radiance at that wavelength and temperature.

Real-world objects are generally nonblackbodies. For instance, the Earth's surface, human skin, and most materials encountered in daily life are nonblackbodies. Their reflectivity and transmissivity vary significantly with wavelength, influencing how they absorb and re-emit energy. This property is crucial in fields like remote sensing, where understanding the spectral characteristics of nonblackbodies is essential for accurate data interpretation. The deviation from ideal blackbody behavior is quantified by the object's emissivity spectrum.