${\displaystyle I_{\text{v}}=\frac{\text{d}{\Phi }_{\text{v}}}{\text{d}\Omega }}$

where Φ_v is the luminous flux emitted in a specified direction, and Ω is the solid angle containing that direction

Note 1 to entry: For practical realization of the quantity, the source is approximated by a point source.

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: Luminous intensity can be derived from the spectral radiant intensity distribution by

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

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

Note 4 to entry: The corresponding radiometric quantity is "radiant intensity". The corresponding quantity for photons is "photon intensity".

Note 5 to entry: The luminous intensity is expressed in candela (cd = lm·sr⁻¹).

Note 6 to entry: This entry was numbered 845-01-31 in IEC 60050-845:1987.