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

where Q_e is the radiant energy emitted, transferred or received, and t is time

Note 1 to entry: The corresponding photometric quantity is "luminous flux". The corresponding quantity for photons is "photon flux".

Note 2 to entry: The term "radiant flux" is the preferred term for most radiometric applications, with the notable exception of laser radiometry where the term "radiant power" is more commonly used.

Note 3 to entry: The radiant flux is expressed in watt (W).

Note 4 to entry: This entry was numbered 845-01-24 in IEC 60050-845:1987.