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]