Term: photon fluence rate, Ep,o
https://doi.org/10.1351/goldbook.P04635

Definition:
Rate of photon fluence. Total number of photons (Np) incident from all directions on a small sphere divided by the cross-sectional area of the sphere and per time interval. SI unit is m-2 s-1. Same as photon spherical irradiance.

Notes:
0) Mathematical definition: Ep,o = dNp/(dt dS) = dHp,o/dt . If Ep,o is constant over the time interval and the surface, Ep,o = Np/tS. Equivalent definition: Ep,o = ∫ 4π Lp ⁢dΩ with Lp the @P04639@ and Ω the solid @A00346@ of the beams passing through the given point on the surface.
1) It reduces to @P04637@ Ep for a parallel and normally incident beam not scattered or reflected by the target or its surroundings.
2) This quantity can be used on a @C01019@ basis by dividing Ep,o by the @A00543@, the symbol then being En,p,o, the name 'photon @FT07376-2@, amount basis', SI unit is mol m-2 s-1; common unit is einstein m-2 s-1.

Related Terms:
1) photon radiance (http://doi.org/10.1351/goldbook.P04639).
2) angle (http://doi.org/10.1351/goldbook.A00346).
3) photon irradiance (http://doi.org/10.1351/goldbook.P04637).
4) chemical amount (http://doi.org/10.1351/goldbook.C01019).
5) avogadro constant (http://doi.org/10.1351/goldbook.A00543).
6) spherical irradiance (http://doi.org/10.1351/goldbook.FT07376-1).
7) fluence rate (http://doi.org/10.1351/goldbook.FT07376-2).

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)

Citation: 'photon fluence rate, Ep,o' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.P04635

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