{"term":{"id":"04634","title":"photon fluence","longtitle":"IUPAC Gold Book - photon fluence","doi":"10.1351\/goldbook.P04634","code":"P04634","status":"current","index":"quantity","definitions":[{"id":1,"text":"Amount of photons (quanta of radiation) incident on a small sphere from all directions, divided by the cross-sectional area of that sphere and integrated over time. Photons per surface area (\\(\\rm{quanta m}^{-2}\\)). SI unit is \\(\\rm{m}^{-2}\\).","notes":{"1":"Mathematical definition: \\(H_{\\rm{p,o}} = F_{\\rm{p,o}} = \\rm{d}N_{\\rm{p}}\/\\rm{d}S = \\int_{t}E_{\\rm{p,o}}\\rm{d}t\\) with \\(E_{\\rm{p,o}}\\) the photon fluence rate, integrated over the duration of the irradiation, \\(t\\). If \\(E_{\\rm{p,o}}\\) is constant over the time interval, \\(H_{\\rm{p,o}} = F_{\\rm{p,o}} = E_{\\rm{p,o}}\\,t\\).","2":"This quantity can be used on a chemical amount basis by dividing \\(H_{\\rm{p,o}}\\) by the Avogadro constant, the symbol then being \\(H_{n\\rm{,p,o}}\\), the name 'photon fluence, amount basis', SI unit is \\(\\pu{mol m-2}\\); common unit is \\(\\pu{einstein m-2}\\)."},"links":[{"term":"Avogadro constant","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/A00543"},{"term":"chemical amount","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/C01019"},{"term":"irradiation","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/I03255"},{"term":"photon fluence rate","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/P04635"}],"sources":["PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 395 (https:\/\/doi.org\/10.1351\/pac200779030293)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/P04634\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/P04634\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/P04634\/plain"},"citation":"Citation: 'photon fluence' 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.P04634","license":"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.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"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.","accessed":"2026-06-06T23:51:15+00:00"}}