"Radiance" is a radiometric measure that describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle in a specified direction.
Applicable units are those of quantitykind:Radiance
http://en.wikipedia.org/wiki/Radiance
https://cdd.iec.ch/cdd/iec61987/iec61987.nsf/ListsOfUnitsAllVersions/0112-2---62720%23UAD148
"Radiance" is a radiometric measure that describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle in a specified direction.
$L = \frac{dI}{dA}\frac{1}{cos\alpha}$, where $dI$ is the radiant intensity emitted from an element of the surface area $dA$, and angle $\alpha$ is the angle between the normal to the surface and the given direction.