Intensity (heat transfer)


In the field of heat transfer, intensity of radiation is a measure of the distribution of radiant heat flux per unit area and solid angle, in a particular direction, defined according to
where
Typical units of intensity are W·m−2·sr−1.
Intensity can sometimes be called radiance, especially in other fields of study.
The emissive power of a surface can be determined by integrating the intensity of emitted radiation over a hemisphere surrounding the surface:
For diffuse emitters, the emitted radiation intensity is the same in all directions, with the result that
The factor is a result of the fact that intensity is defined to exclude the effect of reduced view factor at large values ; note that the solid angle corresponding to a hemisphere is equal to steradians.
Spectral intensity is the corresponding spectral measurement of intensity; in other words, the intensity as a function of wavelength.