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Transmittance
Transmissivity
Atmoshperic Transmissitivity
Transmission Coefficient
(Transmission factor is an old and deprecated
term for transmittance.)
(Terms of radiometry/photometry)
Transmittance is the ratio
of the total radiant or luminous flux
transmitted by a transparent object
to the incident flux, usually given for normal incidence.
Transmissivity
Atmospheric Transmissivity
Transmission coefficient
The ratio of the directly transmitted light after passing through
one unit of a participating medium (atmosphere, dust,
fog) to the amount of light that would have passed the
same distance through a vacuum. It is the amount of light
that remains after the absorption coefficient and
the scattering coefficient (together the
extinction coefficient) are accounted for.
In the Radiance software, those units are used in the
specification of several material types:
- The dielectric and interface material types use RGB transmissivity
values in the sense of the above definition.
- The mist material type calculates its RGB transmission coefficients
as the remainders from the specified extinction coefficients.
- With the trans material types, transmissivity is the fraction of
penetrating light that travels all the way through the material (this
is the transmittance minus any specular reflectance).
- The glass material type requires specification of the
transmissivity at normal incidence, which is defined as the
fraction of light not absorbed in one traversal of the material.
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