absorptance

[inetryconydot]

a measure of the rate of decrease in the intensity of electromagnetic radiation (as light) as it passes through a given substance; the fraction of incident radiant energy absorbed per unit mass or thickness of an absorber

[Ernestdyday]

The ability of an object to absorb radiation, measured as the ratio of absorbed flux to incident flux.

[Zipporah Schumaker]

Absorptance is a measure of the amount of light, or alternatively other electromagnetic radiation, which is absorbed by a particular substance or surface upon which the light is incident. It quantifies the capacity of an object to take in energy from electromagnetic radiation. It is typically represented as a ratio or percentage of the incident radiation that is absorbed.