spectral photon flow, \(\varPhi_{\text{p}\lambda}\)

https://doi.org/10.1351/goldbook.S05820
The photon flow, Φ p, at wavelength λ per unit wavelength interval. The SI unit is s-1 m-1, but a commonly used unit is s-1 nm-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 m-1 and the common unit mol s-1 nm-1.
Source:
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2275 (https://doi.org/10.1351/pac199668122223)