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.
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
(which really should have the units of steradians) 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