{"term":{"id":"04631","title":"photon exitance","longtitle":"IUPAC Gold Book - photon exitance","doi":"10.1351\/goldbook.P04631","code":"P04631","status":"current","synonym":"<em>synonyms<\/em>: photon emittance, specific photon emission","index":"quantity","definitions":[{"id":1,"text":"Photon flux, number basis, \\(q_{\\rm{p}}\\), emitted by an element of the surface containing the source point under consideration divided by the area \\(S\\) of that element. SI unit is \\(\\rm{s}^{-1}\\ \\rm{m}^{-2}\\).","notes":{"1":"Mathematical definition: \\(\\rm{d}q_{p}\/\\rm{d}S\\). If \\(q_{\\rm{p}}\\) is constant over the surface area considered, \\(M_{\\rm{p}} = q_{\\rm{p}}\/S\\).","2":"Formerly called photon emittance.","3":"This quantity can be expressed on a chemical amount basis by dividing \\(M_{\\rm{p}}\\) by the Avogadro constant. In this case the symbol is \\(M_{n\\rm{,p}}\\), the name 'photon exitance, amount basis', SI unit is \\(\\pu{mol s-1 m-2}\\); common unit is \\(\\pu{einstein s-1 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":"exitance","url":"https:\/\/goldbook.iupac.org\/terms\/view\/E02264"}],"sources":["PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 394 (https:\/\/doi.org\/10.1351\/pac200779030293)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/P04631\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/P04631\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/P04631\/plain"},"citation":"Citation: 'photon exitance' 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.P04631","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":"2026-05-10T10:46:07+00:00"}}