generally designates the emission of radiant energy, that is the release of energy stored in material or imparted to it, in the form of optical radiation. Emission is the opposite of absorption.

Earlier designation for relative spectral absorption coefficient K(λ).

Earlier designation for spectral absorbance A(λ). Attenuation of the radiation by absorption and scatter (scattered light) as it passes through the material.

Earlier designation for spectral, absorption coelcient α(λ).Previously referred to as extinction coefficient ελ, is a substance constant used to calculate the concentration of the dissolved substance from the spectral absorbance A according to Lambert-Beer’s law. It is a function of the wavelength and is determined by the absorption spectrum analysis.