07312 IUPAC Gold Book - absorbed photon flux density 10.1351/goldbook.AT07312 AT07312 current synonym: absorbed spectral photon flux density quantity 1 Number of photons of a particular wavelength per time interval (spectral photon flux, number basis, \(q_{\rm{p},\lambda }\), or spectral photon flux, amount basis, \(q_{n,\rm{p},\lambda }\)) absorbed by a system per volume, \(V\). On number basis, SI unit is \(\rm{s}^{-1}\ \rm{m}^{-4}\), and the common unit is \(\rm{s}^{-1}\ \rm{cm}^{-3}\ \rm{nm}^{-1}\). On amount basis, SI unit is \(\pu{mol s-1 m-4}\), and a common unit is \(\pu{einstein s-1 cm-3 nm-1}\). Mathematical expression: \(\frac{q_{p,\lambda }^{0}[1 - 10^{-A(\lambda )} ]}{V}\) on number basis, \(\frac{q_{n,p,\lambda }^{0}[ 1 - 10^{-A(\lambda )} ]}{V}\) on amount basis, where \(A(λ)\) is the absorbance at wavelength \(λ\) and superscript \(0\) (zero) indicates incident photons. Absorbed spectral photon flux density (number basis or amount basis) should be used in the denominator when calculating a differential quantum yield and using in the numerator the rate of change of the number concentration, \(\frac{dC}{dt}\) or the rate of change of the amount concentration, \(\frac{dc}{dt}\), respectively. absorbance https://goldbook.iupac.org//terms/view/A00028 amount concentration https://goldbook.iupac.org//terms/view/A00295 quantum yield https://goldbook.iupac.org//terms/view/Q04991 spectral photon flux https://goldbook.iupac.org//terms/view/S05821 wavelength https://goldbook.iupac.org//terms/view/W06659 PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 297 (https://doi.org/10.1351/pac200779030293) https://goldbook.iupac.org/terms/view/AT07312/html https://goldbook.iupac.org/terms/view/AT07312/json https://goldbook.iupac.org/terms/view/AT07312/plain Citation: 'absorbed photon flux density' 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.AT07312 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. 2026-06-06T20:31:44+00:00