# Description of complex glass systems (geometry + material)

Hi Marina,

1.glazing geometry

Always define glazing object as a polygon, no matter how many layers of
glass it contains in real world.
Double clear, laminated and other glazings differ only in BRTDfunc (light
transmittance and reflectance distribution function), while real glazing
width is not important here.

Note that polygon face should be oriented towards building interior.

···

##########
2.glazing material
Since BRTD function for double glazing is different then for single glazing,
I don't suggest using of simple glass material.
Procedure we use is next:
*Measure each glass layer transmittance and reflectance data. If you can
measure their r,g,b components it is good, if not use the same value for all
3 components.
or
*Export from IGDB (using Optics5 I suppose), each layer separately. And
write down transmittances/reflectances you have in BRTD functions.
Note that in Optics5 front side of the glazing is towards outside, so their
front and Radiance "front" are different.

So you should have next parameters for double glazing parameters after
measures or after export:
rf1 - interior pane front reflectance (towards the room)
rb1 - interior pane back reflectance (towards the exterior pane)
rf2 - exterior pane front reflectance (towards the interior pane)
rb2 - exterior pane back reflectance (towards the exterior)
t1 - interior pane transmittance
t2- exterior pane transmittance
r,g,b - red, green and blue color components
*For clear glass layers front and back reflectance are always the same
*
void BRTDfunc double_glazing
10
if(Rdot,cr(fr(rf1_r),ft(t1_r),fr(rf2_r)),cr(fr(rb2_r),ft(t2_r),fr(rb1_r)))
if(Rdot,cr(fr(rf1_g),ft(t1_g),fr(rf2_g)),cr(fr(rb2_g),ft(t2_g),fr(rb1_g)))
if(Rdot,cr(fr(rf1_b),ft(t1_b),fr(rf2_b)),cr(fr(rb2_b),ft(t2_b),fr(rb1_b)))
ft(t1_r)*ft(t2_r)
ft(t1_g)*ft(t2_g)
ft(t1_b)*ft(t2_b)
0 0 0
glaze2.cal
0
9
0 0 0
0 0 0
0 0 0
*

In glazing definition function
if(Rdot,cr(fr(rf1_r),ft(t1_r),fr(rf2_r)),cr(fr(rb2_r),ft(t2_r),fr(rb1_r)))
means:
-if light is incident to the front side of the glazing then reflectance is
cr(fr(rf1_r),ft(t1_r),fr(rf2_r))
-else (light is incident to the back side) reflectance is
cr(fr(rb2_r),ft(t2_r),fr(rb1_r))

Functions for double glazing reflectance and transmittance are defined
in *glaze2.cal
*script which is provided with Radiance:
-cr(refl1, trans,refl2) - is reflectance distribution for double glazing as
function of light incident angle. refl1 is reflectance of first glazing
pane, refl2 of the second one, and tran1 is transmittance of the first
glazing pane
-ft(t) - transmittance distribution for single glazing as function of light
incident angle. For double glazing total transmittance is ft(t1)*ft(t2)

Hope this helps,
Marija
De Luminae <http://www.deluminaelab.com>