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