Radiance

Radiance is a term in radiometry. It is defined as:

$L={\frac {d^{2}\Phi }{dAd\Omega cos\theta }}$

Where $\Phi$ is radiant flux, $A$ is an area, and $\Omega$ is a solid angle.

Typical units are $[{\frac {W}{m^{2}sr}}]$ where "sr" means steradians.