spectral photon flow, Φ p λ

The photon flow, Φ p, at wavelengthλ 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.
PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2275