[Radiance-general] Prismatic glazings

[Lars O. Grobe]

Hi Marija!

> First question is where to find valid optical and geometrical data
> related to prismatic glazings. On various manufacturers' sites, like
> Siteco or Inglas, there is only some descriptive info ,without any data
> useful for simulations. I've found that some measuremens have been taken
> by Martin Moeck few years ago for Siteco glazings. Are results available
> somewhere?

I am not aware of publicly available measurement data. So probably one 
should start with getting some relieable data measured by one of the 
labs offering such service.

> My idea is to use these glazings in light pipe simulation, on top and/or
> bottom of pipe for light redirection, so I would go with pmap approach.
> Since prism material calculation is not implemented in pmap, I suppose
> some geometrical definition of glazing would be necessary with usage of
> dielectric or interface material and then simulation with pmap.
> Does anyone has some experience with geometrical definition and how much
> accurate it should be (beside examples in Ronald Schregle thesis)?

I have not done a validation in the meaning of comparing with analytical 
and measurement results. However this is one of the core use cases for 
the pmap extension. The pmap approach would be by doing an accurate 
geometrical description and have mkpmap do the forward tracing. As far 
as I understand you are interested in the angular-dependent reflectance 
of the prism sheet in you case, so maybe using a good fit to measurement 
data would also be an option (in that case with "classic" Radiance).

> he put some questions related to Fresnel diffusers simulation. Lars,
> have you succeeded in these simulations? Can you share with us your
> experience?

You can do all this, but be aware that using the pmap means quite a lot 
of fine-tuning. I have modeled light ducts with prism sheets, and got 
some result, but as I said I have not been able to validate it yet 
against measured data. In my opinion doing such comparisions is the 
critical task...

Cheers, Lars.

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