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Radiance's radiation spectrum

Dear Radiance users,

I'm trying to do a conversion of unites from irradiance to photosynthetic photon flux density. In order to do a precise conversion, I need to figure out what spectrum Radiance uses for its calculations. I can't seem to find the answer on Radsite.

Thanks for time!

/Lasse Korsholm

lassebk's avatar
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lassebk
asked 2019-03-01 03:41:02 -0500
__AmirRoth__'s avatar
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__AmirRoth__
updated 2019-03-02 12:53:25 -0500
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1 Answer

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Hi Lasse,

You already started a thread on this on Discourse. I recommend we keep this information together there.

In summary, Radiance does not have an explicit spectrum, just three channels for its ray calculation. You are free to assign these channels however you like. Simply adjust your transmittance and reflectance values in the scene description to adhere to the photosynthetic spectrum rather than the photometric one.

GregWard's avatar
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GregWard
answered 2019-03-04 10:51:13 -0500
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Does this mean we can model the infrared for heating calculations as well?

Determinant's avatar Determinant (2019-03-04 14:00:58 -0500) edit
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Sort of. Radiance doesn't compute or maintain surface temperatures, which you need to compute longwave radiation in a complete thermal calc.

GregWard's avatar GregWard (2019-03-04 14:16:34 -0500) edit
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Thanks for that. I'm going to turn this into a question because I'd like to know if there are any step-by-step procedures on how to do this. Looked online and what I could find was old and incomplete. Just saw the unmethours post. will hold off until I explore that.

Determinant's avatar Determinant (2019-03-04 16:24:38 -0500) edit
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