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.
PAC, 2007, 79, 293
(Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006))
on page 302
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook