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

where Φ_v is luminous flux and A is the area on which the luminous flux is incident

Note 1 to entry: Illuminance can be derived from the spectral irradiance distribution by

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

where K_m is maximum luminous efficacy, E_e,λ(λ) is the spectral irradiance at wavelength λ and V(λ) is spectral luminous efficiency.

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

Note 3 to entry: The illuminance is expressed in lux (lx = lm·m⁻²).

Note 4 to entry: This entry was numbered 845-01-38 in IEC 60050-845:1987.