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

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

Note 1 to entry: The definition holds strictly only for a point source.

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

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

Note 3 to entry: The corresponding photometric quantity is "luminous intensity". The corresponding quantity for photons is "photon intensity".

Note 4 to entry: The radiant intensity is expressed in watt per steradian (W·sr⁻¹).

Note 5 to entry: This entry was numbered 845-01-30 in IEC 60050-845:1987.