The total energy emitted, transferred or received as radiation in a defined period of time (). It is the product of radiant power, , and time, : when the radiant power is constant over the time considered.
PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2268
PAC, 1996, 68, 957 (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 988
ISO 31-5: 1992 (Quantities and Units - Part 5: Electricity and Magnetism.)