spectral radiant intensity, Iλ

https://doi.org/10.1351/goldbook.S05827
The radiation intensity, I at
wavelength
λ per unit
wavelength
interval. The SI unit is W m1 sr1, but a commonly used unit is W nm1 sr1.
Source:
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2276 [Terms] [Paper]