spectral radiant power, \(P_{\lambda}\)

The @R05046@ at @W06659@ \(\lambda \) per unit @W06659@ interval. The SI unit is \(\text{W m}^{-1}\), but a commonly used unit is \(\text{W nm}^{-1}\).
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2276 [Terms] [Paper]
See also:
PAC, 1985, 57, 105. (Names, symbols, definitions and units of quantities in optical spectroscopy (Recommendations 1984)) on page 112 [Terms] [Paper]