spectral photon flux (photon irradiance), \(E_{\text{p}\lambda}\)

https://doi.org/10.1351/goldbook.S05821
The photon irradiance \(E_{\text{p}}\), at wavelength \(\lambda \) per unit wavelength interval. The SI unit is \(\text{s}^{-1}\ \text{m}^{-3}\), but a commonly used unit is \(\text{s}^{-1}\ \text{m}^{-2}\ \text{nm}^{-1}\). Alternatively, the term can be used with the amount of photons (mol or its equivalent einstein), the SI unit then being \(\text{mol}\ \text{s}^{-1}\ \text{m}^{-3}\) and the common unit \(\text{mol}\ \text{s}^{-1}\ \text{m}^{-2}\ \text{nm}^{-1}\).
Source:
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2275 [Terms] [Paper]