Solar irradiance at sea level, i.e., traversing the atmosphere, when the direction of the sun is perpendicular to the surface of the earth. Also called terrestrial global irradiance.
See also: AM 0 sunlight
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 302 (https://doi.org/10.1351/pac200779030293)