The number of photons (quanta, N) per unit time. (dN/dt, simplified expression: Φ p = N t when the number of photons is constant over the time considered). The SI unit is s-1. Alternatively, the term can be used with the amount of photons (mol or its equivalent einstein), the SI unit then being mol s-1.
See: spectral photon flow
See also: radiant power
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2263 (https://doi.org/10.1351/pac199668122223)