|Definition:|| qualifies or supplements a quantity name to indicate the quotient of that quantity by the wavelength or the frequency
Note 1 to entry: The wavelength is used mainly in optics, and the frequency in radioelectricity, acoustics, and signal theory. Examples: power spectral density, spectral irradiance.
Note 2 to entry: The adjective “spectral” is also used to designate quantities which are functions of wavelength or frequency, but which are not spectral concentrations, for example spectral emissivity. See IEV 845-01-16.