spectral quantities

Quantities characterizing electromagnetic radiation (radiant power, energy, energy density, intensity, exitance, radiance, irradiance, etc.) derived by differentiation with respect to wavelength, frequency or wavenumber, e.g. spectral (concentration of) irradiance is the derivative of the irradiance with respect to wavelength (Eλ), frequency (Eν) or wavenumber (Eν˜).
Green Book, 2nd ed., p. 31 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)