[Radiance-general] translucent panel ( trans material )

[Jack de Valpine]

Hi Coralie and Achim,

A couple of comments. Optics 5 models thermal and spectral optical 
properties of a wide range of glazing based on measured data. However it 
does not contain a model for for diffusely transmitting materials. So 
for modeling complex glazing systems and exporting data for use in the 
"glaze" script it is a great place to start, however it will not help 
with the kind of data that it looks like Coralie has available, which 
suggests a material with a large diffuse transmitting component.

There are a few things to note about the information that Coralie 
provided. One is that it looks like one side is "shiny" or specular 
while the other is "mat" or diffuse. The trans material will not give 
you control over what happens on each side of the material. Based on 
this alone it is likely that this is a material that would be better 
characterized using the BRTDfunc material type. This allows for more 
flexibility in describing material behavior. However, this being said 
there is one thing that is a little puzzling (there are others who may 
chime in on this who know more), this is that your measurments show 
different transmittance (total) depending on the side of the material. 
Is this possible? This certainly cannot be modeled with the "trans" 
material type.

Regards,

-Jack de Valpine

-- 
# Jack de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction



Achim Geissler wrote:
>
> Dear Coralie
>
>  
>
> if you have the full spectro-data, there may be a different path: 
> There is a tool called “glaze” (a script found in the standard 
> radiance installation). With this script, you can convert Optics 
> (“Optics” being the freeware program from the LBNL) spectral data into 
> a more detailed Radiance description (type “BRTDfunc”) by exporting 
> from Optics in “Radiance Format” and then entering this data in the 
> “glaze” script.
>
>  
>
> I am laboring under the possible delusion that this is generally a 
> better description for “advanced” glazing products (and possibly any 
> translucent materials). However, I am quite new at this.
>
>  
>
> Regards
>
> Achim
>
>  
>
>  
>
> *From:* radiance-general-bounces at radiance-online.org 
> [mailto:radiance-general-bounces at radiance-online.org] *On Behalf Of 
> *Coralie Cauwerts
> *Sent:* Donnerstag, 17. Dezember 2009 11:01
> *To:* radiance-general at radiance-online.org
> *Subject:* [Radiance-general] translucent panel ( trans material )
>
>  
>
> Hello Everyone,  
>
>  
>
> I know characteristics of a 4mm thick translucent panel (measured with 
> a spectrophotometer). I try to introduce it in RADIANCE.
>
>  
>
> Measurements on the exterior side (glossy) give :
>
> Transmittance_diffuse = 75.5% and transmittance_spec = 9.1%
>
> Reflectance_diffuse = 7.7%
>
> Absorptance = 7.8%
>
>  
>
> Measurements on the interior side (mat) give :
>
> Transmittance_diffuse = 81.6% and transmittance_spec = 8.9%
>
> Reflectance_diffuse = 7.8%
>
> Absorptance = 1.6%
>
>  
>
> I’m not sure that I introduced it in RADIANCE in a correct way …
>
> (following formulas p325 in Rendering with Radiance)
>
> void trans vitr_dif
>
> 0
>
> 0
>
> 7     0.71 0.77 0.77 0 0.1 0.99 0.0012
>
> With
>
> Cr = 0.074
>
> Cg = 0.08
>
> Cb = 0.08
>
> Rd = 0.265*Cr+0.67*Cg+0.065*Cb = 0.07841
>
> Rs = 0
>
> Sr = 0.1
>
> Td = 75.5
>
> Ts = 0.091
>
>  
>
> Thank you for your help !
>
>  
>
> Coralie
>
>  
>
> *-----------------------------------------------------------------------------------------
> *Coralie Cauwerts
>
> Researcher
>
> Université catholique de Louvain
>
> Belgium
>
>  
>
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>
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