\(L_v = \frac{dI_v}{dA}\), where \(dI_v\) is the luminous intensity of an element of the surface with the area \(dA\) of the orthogonal projection of this element on a plane perpendicular to the given direction.
n3:plainTextDescription
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle.