spectral radiance, L λ

Th e radiance, $L$ , at wavelength $λ$ 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