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RADIANCE Three-Phase Method - modeling only clear glass

Hi everyone, I have a very simple question about the RADIANCE matrix multiplication methods: Is it correct to go through all the steps of the Five-Phase method to simulate a simple clear glass window? I mean, without any blinds or lighting redirecting device, just clear glass. I thought it would be more accurate because of the sun coefficient calculation, but I’m getting many negative numbers, and also notice that in the tutorial, it is given the example of using clear glass (clear.xml) only in the Three-phase section, for the Three-phase-direct they use already blinds in the example (blinds.xml).

While that would be my main question, I take the opportunity to ask, if for the Sun-Coefficient calculation should be better to use a combination of BSDF (genBSDF), and 'glass material' (like in the tutorial), instead of the blend that we get when adding the 'glass material' using Window LBNL. I ask this because I’ve notice some very high peaks of illuminance (15k + lux), when I use the system created with Window LBNL. This numbers are shown few times in a year-calculation, but are a bit inconsistent with the overall results, and I guess this would be also an issue in images generated for a glare evaluation.

I'd appreciate your help regarding this question Thanks Steph