The three-dimensional spectrum generated by scanning the emission spectrum at incremental steps of excitation wavelength (x axis = emission wavelength, y axis = excitation wavelength, z axis = emission flux) is called a (fluorescence, phosphorescence) excitation-emission spectrum (or EES). The spectra are particularly useful for investigating samples containing more than one emitting species. Corrected EES are obtained if (a) the emission is corrected for instrumental response with wavelength, and (b) the exciting radiation flux in photons s-1 is held constant for all excitation wavelengths.