photon flux, qp, Φp

Number of photons (quanta of radiation, $N p$ ) per time interval. SI unit is $s −1$ .

Notes:

Mathematical definition: $q p = d N p / d t$ . If the number of photons is constant over the time interval, $q p = N p / t$ .
This quantity can be used on a chemical amount basis by dividing the photon flux, number basis, $q p$ , by the Avogadro constant, the symbol then being $q n , p$ , the name 'photon flux, amount basis', SI unit is $mol s −1$ ; common unit is $einstein s −1$ .
Although the symbol recommended by CEI is $Φ p$ , the symbol $q p$ 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

photon flux, ,