${\displaystyle M_{\text{v}}=\frac{\text{d}{\Phi }_{\text{v}}}{\text{d}A}}$

where Φ_v is luminous flux and A is the area from which the luminous flux leaves

Note 1 to entry: Luminous exitance can be derived from the spectral radiant exitance distribution by

$M_{\text{v}}=K_{\text{m}}{\displaystyle \underset{0}{\overset{\infty }{\int }}{M}_{\text{e}\text{,}\lambda }(\lambda )V(\lambda )\text{d}\lambda }$

where K_m is maximum luminous efficacy, M_e,λ(λ) is the spectral radiant exitance at wavelength λ and V(λ) is spectral luminous efficiency.

Integral limits can be confined depending on the spectral responsivity of the detectors used as a sensor.

Note 2 to entry: The corresponding radiometric quantity is "radiant exitance". The corresponding quantity for photons is "photon exitance".

Note 3 to entry: The luminous exitance is expressed in lumen per square metre (lm·m⁻²).

Note 4 to entry: This entry was numbered 845-01-48 in IEC 60050-845:1987.