The transfer of energy by radiation is given by the Stefan Boltsmann law. This equation tells us that, as the temperature of a black body increases, the amount of heat power it emits increases as the fourth power of the temperature. Thus, if we double the temperature, the amount of energy emitted will increase sixteen times. The radiation striking the surface is either reflected, absorbed, or transmitted. Reflected radiation basically bounces off the surface.
Absorbed radiation is the energy the surface captures, just as a sponge soaks up water.
The Greek symbol a is used to indicate absorptivity. Transmitted radiation is energy that passes through. Due to conservation of energy, all of the radiation must be accounted for. So the sum of the reflected, absorbed, and transmitted radiation must equal the incoming energy. The emitted wavelengths depend on the material properties and temperature.