Number of photons (quanta of radiation,
per time interval (photon flux),
leaving or passing through
a small transparent element of
surface in a given direction from the source about the solid angle
divided by the solid angle
and by the orthogonally projected area of the element in a
plane normal to the given beam direction,
between the normal to the surface and the direction of the beam.
Equivalent definition: Integral taken over the hemisphere visible
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