07376 IUPAC Gold Book - fluence rate 10.1351/goldbook.FT07376 FT07376 current mentioned: spherical irradiance synonym: radiant energy fluence rate quantity 1 Total radiant power, \(P\), incident from all directions onto a small sphere divided by the cross-sectional area of that sphere. SI unit is \(\rm{W m}^{-2}\). Mathematical definition: \(E_{\rm{o}} = \frac{\rm{d}P}{\rm{d}S} = \frac{\rm{d}H_{\rm{o}}}{\rm{d}t}\). If the radiant power is constant over the area \(S\), \(E_{\rm{o}} = \frac{P}{S}\). Equivalent definition: \(E_{\rm{o}} = \int_{4\pi}L\rm{d}\varOmega\), with \(\varOmega\) the solid angle of each beam passing through the given point on the surface and \(L\) the radiance of the beam at that point. Fluence rate is identical to spherical irradiance and reduces to irradiance, \(E\), for a parallel and perpendicularly incident beam not scattered or reflected by the target or its surroundings. angle https://goldbook.iupac.org//terms/view/A00346 irradiance https://goldbook.iupac.org//terms/view/I03254 radiance https://goldbook.iupac.org//terms/view/R05037 radiant power https://goldbook.iupac.org//terms/view/R05046 PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 340 (https://doi.org/10.1351/pac200779030293) https://goldbook.iupac.org/terms/view/FT07376/html https://goldbook.iupac.org/terms/view/FT07376/json https://goldbook.iupac.org/terms/view/FT07376/plain Citation: 'fluence rate' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.FT07376 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-06-06T23:49:31+00:00