Preferred Label : photon radiance;
Detailed label : photon radiance, Lp;
IUPAC definition : Number of photons (quanta of radiation, Np) per time interval (photon flux), qp,
u leaving or passing through /u a small transparent element of surface in a given
direction from the source about the solid angle Ω, divided by the solid angle and
by the orthogonally projected area of the element in a plane normal to the given beam
direction, dS dS cos θ, with θ the angle 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 Lp.cos θ.dΩ, with Lp the photon radiance
at the given point in the various directions of the incident beam of solid angle Ω
and θ the angle between any of these beams and the normal to the surface at the given
point.;
Scope note : this quantity can be used on a chemical amount basis by dividinglpby the avogadro
constant, the symbol then being ln,p, the name photon radiance, amount basis. for
a divergent beam si unit is mol m-2 s-1 sr-1;common unit is einstein m-2
s-1 sr-1. for a parallel beam si unit is mol m-2 s-1;common unit is einstein
m-2 s-1.; for a parallel beam it is the number of photons (quanta of radiation, np) per time
interval (photon flux),qp, leaving or passing through a small element of surface in
a given direction from the source divided by the orthogonally projected area of the
element in a plane normal to the given direction of the beam,¿. mathematical definition
in this case: lp s¿ qp ifqp is constant over the surface area considered,
lp qp s¿ ,si unit is m-2 s-1.; mathematical definition: lp ¿ s¿ qp ¿ s¿ qp
for a divergent beam propagating in an elementary cone of the solid angle ¿ containing
the direction¿.si unit is m-2 s-1 sr-1.;
Origin ID : P04639;
See also
Number of photons (quanta of radiation, Np) per time interval (photon flux), qp,
u leaving or passing through /u a small transparent element of surface in a given
direction from the source about the solid angle Ω, divided by the solid angle and
by the orthogonally projected area of the element in a plane normal to the given beam
direction, dS dS cos θ, with θ the angle 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 Lp.cos θ.dΩ, with Lp the photon radiance
at the given point in the various directions of the incident beam of solid angle Ω
and θ the angle between any of these beams and the normal to the surface at the given
point.
