https://doi.org/10.1351/goldbook.R05041
Radiant power, \(P\), emitted at all wavelengths by an element of surface containing the source point under consideration divided by the area of the source. SI unit is \(\rm{W m}^{-2}\).
Notes:
- Mathematical definition: \(M = \rm{d}P/\rm{d}S\). If the radiant power \(P\) is constant over the surface area considered, \(M = P/S\).
- Equivalent to the integration of the radiant power leaving a source over the solid angle and over the whole wavelength range. Mathematical definition: \(M = \int_{\lambda}M_{\lambda}\, \rm{d}\lambda\), where \(M_{\lambda}\) is the spectral radiant exitance at wavelength \(\lambda\).
- Same as spherical radiant exitance. Formerly called radiant emittance.