[help] how to get short-wave and long-wave solar radiation value?

Dear Radiance experts,

May I ask whether it's possible to "isolate" the contribution of short-wave
and long-wave solar radiation using Radiance?

One of our colleagues wants to get these values for the calculation of "mean
radiant temperature" for the purpose of analyzing the implications of urban
geometries on thermal comfort.

Correct me if I'm wrong, the irradiation value obtained in Radiance is the
total solar radiation energy received on a given surface.

So, is this "total" value encompasses the full spectrum of solar radiation,
including the visible part and the short-wave and long-wave parts that are
not visible to human eyes?

If it is, then, is there a way to single out the contribution from
short-wave and long-wave radiation separately?

Clarification and advices are deeply appreciated!

- Cheers, Ji

Hi Ji Zhang!

May I ask whether it's possible to "isolate" the contribution of
short-wave and long-wave solar radiation using Radiance?

One of our colleagues wants to get these values for the calculation of
"mean radiant temperature" for the purpose of analyzing the implications
of urban geometries on thermal comfort.

Correct me if I'm wrong, the irradiation value obtained in Radiance is
the total solar radiation energy received on a given surface.

So, is this "total" value encompasses the full spectrum of solar
radiation, including the visible part and the short-wave and long-wave
parts that are not visible to human eyes?

If it is, then, is there a way to single out the contribution from
short-wave and long-wave radiation separately?

Clarification and advices are deeply appreciated!

You are (almost) completely free to choose what wavelength range to squeeze into any of the three channels that we usually refer to as RGB. So instead of calling the first channel "RED", you could call it "Shortwave". As long as you use the three channels for the same wavelength ranges when defining materials, sources, and interpreting results, that is fine for radiative transfer of energy.

However I would advice not to make use of the possibility of rendering all these wavelength ranges at once by making use of the three channels. It would be better to set all three channels to the same wavelength range, so work with "neutral grey" lights and surfaces. The reason is that there are some (few) parts of Radiance's code where the channels are weighted according to human perceiption assuming RGB-like wavelengths.

Another question is how to find how much of the absorped short-wave solar irradiation may get emitted as long-wave radiation by a surface. Radiance does not consider such "shift" effects. So IR radiation by surfaces heating up in the sun would not be reflected.

Cheers, Lars.