photon fluence rate, $E p , o$

Rate of photon fluence. Total number of photons ( $N p$ ) 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:

Mathematical definition: $E p , o = d N p / d t d S = d H p , o / d t$ . If $E p , o$ is constant over the time interval and the surface, $E p , o = N p / t S$ Equivalent definition: $E p , o = ∫ 4 π L p ⁢ d Ω$ with $L p$ the photon radiance and $Ω$ the solid angle of the beams passing through the given point on the surface.
It reduces to photon irradiance $E p$ for a parallel and normally incident beam not scattered or reflected by the target or its surroundings.
This quantity can be used on a chemical amount basis by dividing $E p , o$ by the Avogadro constant, the symbol then being $E n , p , o$ , the name 'photon fluence rate, amount basis', SI unit is $mol m −2 s −1$ ; common unit is $einstein m −2 s −1$ .

Source:

PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 395

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IUPAC > Gold Book > math/physics > quantities

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Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook.

Last update: 2014-02-24; version: 2.3.3.

DOI of this term: https://doi.org/10.1351/goldbook.P04635.

Original PDF version: http://www.iupac.org/goldbook/P04635.pdf. The PDF version is out of date and is provided for reference purposes only. For some entries, the PDF version may be unavailable.

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