Spectral performance describes how closely the emitted spectrum of a solar simulator reproduces the reference solar spectrum such as AM1.5G or AM0.
Accurate spectral reproduction is essential because photovoltaic devices often exhibit wavelength-dependent responses. If the illumination spectrum differs significantly from the standard solar spectrum, the measured device performance may not represent real solar operating conditions.
Spectral performance is typically evaluated using a spectroradiometer, which measures spectral irradiance over the relevant wavelength range.