04636
photon flux
IUPAC Gold Book - photon flux
10.1351/goldbook.P04636
P04636
current
abbrev: CEI
quantity
-
1
Number of photons (quanta of radiation, \(N_{\rm{p}}\)) per time interval. SI unit is \(\rm{s}^{-1}\).
- Mathematical definition: \(q_{\rm{p}} = \rm{d}N_{\rm{p}}/\rm{d}t\). If the number of photons is constant over the time interval, \(q_{\rm{p}} = N_{\rm{p}}/t\).
- This quantity can be used on a chemical amount basis by dividing the photon flux, number basis, \(q_{\rm{p}}\), by the Avogadro constant, the symbol then being \(q_{n\rm{,p}}\), the name 'photon flux, amount basis', SI unit is \(\pu{mol s-1}\); common unit is \(\rm{einstein s}^{-1}\).
- Although the symbol recommended by CEI is \(\mathit{\Phi} _{\rm{p}}\), the symbol \(q_{\rm{p}}\) is preferred since \(\mathit{\Phi}\) is reserved for quantum yield.
-
Avogadro constant
https://goldbook.iupac.org//terms/view/A00543
-
chemical amount
https://goldbook.iupac.org//terms/view/C01019
-
quantum yield
https://goldbook.iupac.org//terms/view/Q04991
- PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 395 (https://doi.org/10.1351/pac200779030293)
https://goldbook.iupac.org/terms/view/P04636/html
https://goldbook.iupac.org/terms/view/P04636/json
https://goldbook.iupac.org/terms/view/P04636/plain
Citation: 'photon flux' 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.P04636
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.
2026-06-06T22:37:10+00:00