spectral radiance, L λ

https://dx.doi.org/10.1351/goldbook.S05824
Th e radiance, L, at wavelengthλ per unit wavelength interval. The SI unit is W m −3 sr −1, but a commonly used unit is W m −2 sr −1 nm −1.
Source:
PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2276