The rate of
photon fluence.
Four times the ratio of the
photon flow,
, incident on a small, transparent, imaginary spherical volume element containing the point under consideration divided by the surface of that sphere,
.
(
, simplified expression:
when the
photon flow is constant over the solid
angle considered). The SI unit is
.
Alternatively, the term can be used with the amount of photons (mol or its equivalent
einstein), the SI unit then being
.
It reduces to
photon irradiance
for a parallel and normally incident beam not scattered or reflected by the target or its suroundings.
Source:
PAC, 1996, 68, 2223
(Glossary of terms used in photochemistry (IUPAC Recommendations 1996))
on page 2263
