Energy Flux -- from Eric Weisstein's World of Physics

The mean energy flux is , also written as and called I, the intensity. For a traveling wave,

The unit of energy flux is 1 J m^-2 s^-1 = 1 kg s^-3.

For radiation, consider a half-plane filled with energy density u, then

where c is the speed of light, is the angle from the propagation axis, a is the radiation constant, T is the temperature, and is the Stefan-Boltzmann constant.

Energy, Intensity, Luminosity, Poynting Flux

References