PROPERTIES OF REAL SURFACES
Following from: The blackbody
The characteristics of the blackbody are independent of material properties and its emission properties depend only on the independent parameters T and λ or their product. Real materials absorb (and therefore emit) less thermal radiation than predicted for a blackbody. To account for the differences between the ideal blackbody and the performance of real materials, the radiative properties of opaque surfaces are used.
1 RADIATIVE PROPERTIES OF OPAQUE SURFACES
Emitted or absorbed intensity is independent of angle for the blackbody; however, the surface properties of real materials are angularly dependent, i.e., the intensity emitted by a real surface may vary with respect to the angle relative to the surface normal, as does the ability of the surface to absorb radiation. There is sparse data for the angular dependence of s ...