Description of complex glass systems (geometry + material)

Hi Marina,

Yes you want to describe the glass geometry, that is one polygon representing the multiple layers of the physical makeup. The material is what should represent the behavior. If you take the output from Optics and run it through optics2rad you will get a single BRTDfunc material description. One thing to be careful of is that this is dependent on the correct orientation (normal) of the glass geometry. I believe that the normal is supposed to be pointing "into" the interior of the building. One way to check normal orientation in radiance is to assign (temporaryily) a "glow" material to the glass geometry and view it. The sides that are "black" are the back sides of the geometry, the sides that are not black are the positive normal side.


-Jack de Valpine

marina aviles olmos wrote:


Hi everybody,

I have two questions about the description of a glass facade with a
complex glass system: one about the geometry and one concerning the

1-. With the objective in daylight calculations and daylight efficiency
of materials I try to simulate, so accurate as possible, a doble glazing
facade with the next composition:

9mm laminated glass with spectrally selective interlayer -- 16mm air --
4mm float glass

All the papers I've read describe the glass geometry as polygon as follows:

mod polygon id
3n x1 y1 z1
    x2 y2 z2
    xn yn zn

In my case, with such a glass system, would be this geometry
description of the glass right and accurate? or should I define the
radiance geometry like the contructed geometry?

2-. The second question is about the material description.
I have measured the transmittance of this doble glazing material sample
with a Spectrometer and an accessory for external measurements and
computed its transmissivity.
The complete definition of the material that I get is as follows:

mod glass id
3 rtn gtn btn

On the other hand I have exported in Radiance format from the software
Optics5 a similar glass, also with sun protection interlayer, and the
material description is much complexer. It is as follows:

void glass sunstop-t-silver-20_glass
3 0,205 0,222 0,239

void BRTDfunc sunstop-t-silver-20_front
      0,325 0,281 0,197
      0,188 0,203 0,219
      0 0 0
9 0 0 0 0 0 0 0 0 0

void BRTDfunc sunstop-t-silver-20_back
      0,259 0,289 0,307
      0,188 0,203 0,219
      0 0 0
9 0 0 0 0 0 0 0 0 0

My question is if the description I did is complete and will give an
accurate calculation.
In case it is not, how can I get the hole description with the BRTD
information if I just have the glass sample and the Spektrometer to
start and this glass is not in the IGDB?

Thank you,


# Jack de Valpine
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