We now continue with the topic of radiation transport first introduced in Section 1.3. After a brief review of applications of radiative heat transfer in micro-electronics manufacturing equipment, we present a more detailed look at radiation scattering in semi-transparent materials. The results of Chapter 1 for scattering off opaque surfaces are extended to semi-transparent materials through the use of effective optical properties. In particular this allows an effective description of solids coated with thin film layers. Such surfaces appear frequently in micro-electronics processing. The dependence of general optical properties of surfaces on temperature and wavelength of radiation is also addressed.