Definition
Consider a unit of surface area. Realistically, the radiant intensity from emitted radiation, and the intensity of reflected radiation, are both functions of angle from the surface. So, adding these together, the intensity of the total radiation leaving the surface is defined as
where represents energy flux and is the solid angle. The term accounts for the projected area of the surface at an angle. Now, to find the radiosity, the flux is integrated over a hemispherical surface enclosing the unit area for all angles. To generalize further, the radiosity should also be expressed as a function of the wavelength of the radiation .
Assuming a diffuse emitter and reflector, is constant and the radiosity reduces to over all wavelengths. Furthermore, for a blackbody, and the radiosity reduces to .
Read more about this topic: Radiosity (heat Transfer)
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