photon flux, qp, Φp 

https://doi.org/10.1351/goldbook.P04636
Number of photons (quanta of radiation, Np) per time interval. SI unit is s−1.
Notes:
  1. Mathematical definition: qp=dNp/dt. If the number of photons is constant over the time interval, qp=Np/t.
  2. This quantity can be used on a chemical amount basis by dividing the photon flux, number basis, qp, by the Avogadro constant, the symbol then being qn,p, the name 'photon flux, amount basis', SI unit is mols−1; common unit is einstein s−1.
  3. Although the symbol recommended by CEI is Φp, the symbol qp is preferred since Φ is reserved for quantum yield.
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 395 [Terms] [Paper]
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. https://doi.org/10.1351/goldbook.P04636 RIS BibTex EndNote
Div. IIIPDFTextXMLJSONQuantity
Last revised: February 24, 2014