Intensity (heat transfer)
- is the infinitesimal source area
- is the outgoing heat transfer from the area
- is the solid angle subtended by the infinitesimal 'target' (or 'aperture') area
- is the angle between the source area normal vector and the line-of-sight between the source and the target areas.
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 (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 steradians.