https://dx.doi.org/10.1351/goldbook.P04633
The number of photons (quanta, 
) per unit time. (
, simplified expression: 
when the number of photons is constant over the time considered). The SI unit is 
. Alternatively, the term can be used with the amount of photons (mol or its equivalent einstein), the SI unit then being 
.
) per unit time. (, simplified expression: when the number of photons is constant over the time considered). The SI unit is . Alternatively, the term can be used with the amount of photons (mol or its equivalent einstein), the SI unit then being . See: spectral photon flow
See also: radiant power
Source:
PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2263