The amount of radiant energy flux expressed in terms of the solar spectrum. NREL's Solar Spectral Radiation Data Base contains thousands of irradiance spectra.

The radiant flux density incident on a surface, resolved spectrally. (W/m2/um).

see spectral flux

Energy at a specific wavelength radiated onto an object of unit area per unit time. Standard measurement unit W m-2 µm-1.

The monochromatic irradiance of a surface per unit bandwidth at a particular wavelength, usually expressed in Watts per square meter-nanometer bandwidth.

The irradiance per unit wavelength or wavenumber interval. Units are typically W m−2 μm−1 or W m−2(cm−1)−1.