Equivalent definition. Integral, taken over the hemisphere visible from the given point, of the expression L_e · cos θ · dΩ, where L_e is the radiance at the given point in the various directions of the incident elementary beams solid angle dΩ, and θ is the between any of these beams and the normal to the surface at the given point

${\displaystyle E_{\text{e}}=\frac{\text{d}{\Phi }_{\text{e}}}{\text{d}A}={\int }_{2\pi \text{sr}}{L}_{\text{e}}\cdot \cos \theta \cdot \text{d}\Omega }$

unit: W • m^-2