Number of photons (quanta of radiation,
per time interval (photon flux),
from all upward
directions on a small element of surface
containing the point under consideration divided by the area of the element.
SI unit is
Equivalent definition: Integral, taken over the
from the given point, of the expression
the photon radiance
at the given point in the
various directions of the incident beam of solid angle
between any of these beams and the normal to the surface at the given point.
PAC, 2007, 79, 293
(Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006))
on page 396
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