radiant (energy) flux [obsolete], P, Φ 

https://doi.org/10.1351/goldbook.R05044
This obsolete term is not recommended. In photochemistry, radiant power, P, is adopted. SI unit is W.
Note:
P is preferred, because in photochemistry, Φ is reserved for quantum yield.
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 409 [Terms] [Paper]
Citation: 'radiant (energy) flux' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.R05044 RIS BibTex EndNote
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Last revised: February 24, 2014