https://doi.org/10.1351/goldbook.S05824
The radiance, \(L\), at wavelength \(\lambda \) per unit wavelength interval. The SI unit is \(\rm{W m}^{-3}\ \rm{sr}^{-1}\), but a commonly used unit is \(\rm{W m}^{-2}\ \rm{sr}^{-1}\ \rm{nm}^{-1}\).