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 @C01019@ basis by dividing the photon flux, number basis, qp, by the @A00543@, the symbol then being qn,p, the name 'photon flux, amount basis', SI unit is mol s-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 @Q04991@.
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)