The relationship between absorbtion, emissivity and reflection

[swampwiz]

As I understand it, the absorption coefficient of a surface of material is the same as its emissivity (due to Kirchoff's law of thermal radiation), and that the net of this and the tranmissibility is

emissivity + reflectivity + transmissibility = 1

Is this a general statement about any radiation, or only about thermal "black-body" radiation?

I presume that the tranmissibility is the initial transmissibility of the surface, since once inside the body of the material, there is absorption, which is termed attenuation, in which the transmitted radiation is slowly absorbed as it goes through the body. How are these 2 forms of absorption related?

 

[Andy Resnick]

That is a general statement, and a consequence of conservation of energy.