Absorption

This is property of material to convert the radiation they receive (such as light) into different forms of energy, mostly heat. A measure of this property is the degree of absorption a = Fa / F, the ratio of the luminous flux absorbed to the incident luminous flux. (Reflection, Transmittance).
 
a = Fa / F
 
F  = incident luminous flux
Fa = absorbed luminous flux
Fr = reflected luminous flux
Ft = transmitted luminous flux

Reflection, Absorption and Transmission in schematic format
Zatvori