Title: photon fluence
Long Title: IUPAC Gold Book - photon fluence
DOI: 10.1351/goldbook.P04634
Status: current
Index: quantity

Definition
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 \(\pu{einstein m-2}\).

Related Terms
- Avogadro constant: https://goldbook.iupac.org/terms/view/A00543
- chemical amount: https://goldbook.iupac.org/terms/view/C01019
- irradiation: https://goldbook.iupac.org/terms/view/I03255
- photon fluence rate: https://goldbook.iupac.org/terms/view/P04635

Source
- PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 395 (https://doi.org/10.1351/pac200779030293)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/P04634/html
- json: https://goldbook.iupac.org/terms/view/P04634/json
- xml: https://goldbook.iupac.org/terms/view/P04634/xml

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
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Accessed: 2026-07-30T19:26:15+00:00