In radiometry, a radiant energy is the energy of some electromagnetic radiation which is emitted, transmitted or absorbed during some interval of time. The corresponding photometric quantity is the luminous energy Qv.
The term radiant energy is common in fields like illumination and radiative heating (with infrared radiation), but less so in laser technology, where it is more common to use the term pulse energy for the energy in an optical pulse.
Many radiometric quantities are derived from the radiant energy. For example, the radiant flux is the radiant energy per unit time, which in optics corresponds to the optical power. A radiant exposure is the received radiant energy per unit area.