The field of photovoltaics uses the Air Mass 1.5 solar irradiance spectrum. This is the energy spectrum received at sea level when the sun is at a zenith angle of 48.18° and so
corresponds to an atmospheric thickness 1.5 times that of AM1. The ASTM E173 standard contains standard tables for the Air Mass 1.5 spectrum and replaces previous standards (E891, E892).