[Bldg-sim] Correction Factor in Radiance

[Lars O. Grobe]

Hi Sowgol,

just as Rob wrote, just use the physical properties in your geometry and
scene description.

Radiance's basic unit is - surprise - radiance [W/m2sr]. If you want to
derive photometric values from radiometric onces, you typically use a
luminous efficacy of 179 in Radiance. Or you rely on its analysis tools
doing the conversion for you such as pvalue, falsecolor.

If glazing is not clean, I would expect transmission through it to get
reduced plus extra scattering. It depends on you application whether
scattering is of importance (e.g. a really dirty glazing exposed to
direct sun may lead to glare). Reduced transmission may be accounted for
by using it in you glass material definition (probably you should know
the reduction, which would require measurements). Heavy scatter could(!)
lead to using a different material type instead. An example: reduced
transmission would make your window pane just appear darker when viewed.
Increased scatter e.g. due to a layer of dust particles would make it
appear brighter when viewed directly except sources directly visible,
which would appear darker. In other terms, the scatter would distribute
the bright spot of the source over a wider area. That would make it
appear to have a bright film over the entire pane, while a perfectly
clear glazing would be dark with the source directly seen appearing at
its full brightness.

The important thing to remember (always) is that there is no such thing
as a correction factor in Radiance. It is all about physical units. If
results appear to be wrong, do not multiply but find the source of error.

Cheers, Lars.

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