Note 1 to entry: Radiant energy can be expressed by the time integral of radiant flux, Φ_e, over a given duration, Δt:

$Q_{\text{e}}={\displaystyle {\int }_{\Delta t}{\Phi }_{\text{e}}}\text{d}t$

Note 2 to entry: Radiant energy is expressed as a function of wavelength, λ, as a function of frequency, ν, or as a function of wavenumber, σ.

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

Note 4 to entry: The radiant energy is expressed in joule (J = W·s).

Note 5 to entry: This entry was numbered 845-01-27 in IEC 60050-845:1987.