${\displaystyle {\Phi }_{\text{v}}=\frac{\text{d}{Q}_{\text{v}}}{\text{d}t}}$

where Q_v is the luminous energy emitted, transferred or received, and t is time

Note 1 to entry: Luminous flux is a quantity derived from the radiant flux, Φ_e, by evaluating the radiation according to its action upon the CIE standard photometric observer. Luminous flux can be derived from the spectral radiant flux distribution by

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

where K_m is maximum luminous efficacy, Φ_e,λ(λ) is spectral radiant flux, V(λ) is spectral luminous efficiency and λ is wavelength.

Note 2 to entry: The distribution of the luminous intensities as a function of the direction of emission, e.g. given by the polar angles (ϑ, φ), is used to determine the luminous flux, Φ_v, within a certain solid angle, Ω, of a source:

${\Phi }_{\text{v}}={\displaystyle \underset{\Omega }{\iint }{I}_{\text{v}}\left(\vartheta ,\phi \right)\text{sin}\vartheta \text{ d}\phi \text{ d}\vartheta }$.

Note 3 to entry: The corresponding radiometric quantity is "radiant flux". The corresponding quantity for photons is "photon flux".

Note 4 to entry: The luminous flux is expressed in lumen (lm).

Note 5 to entry: This entry was numbered 845-01-25 in IEC 60050-845:1987.