[Radiance-general] Determining Specularity Values - Spandrel Panels: Marble vs Fritted Glass

[Thomas Bleicher]

On 4 Nov 2008, at 14:49, Pearson, Nastassja wrote:

> I have some questions about determining/selecting material  
> properties, specifically deciding what material type (plastic/ 
> metal) and secularity to use for the two cladding options.
>
> My assumptions:
>
> Marble – Originally white, but panels have become grey with dirt  
> over time, not polished, dull finish
>
> Type:                Plastic
>
> Colour:             (0.91, 0.91, 0.83)
>

As Randolph wrote this is far too 'white' for a typical white material,
especially if it's a bit dirty.

0.75 throughout would be the colour of white wallpaint, so dirty marble
might be in the range of 0.6 to 0.65 (just a guess).

> Specularity:       ?????? (I think this may be low because it is  
> not polished marble)
>
> Roughness:      0.05 (???)
>
Specularity and roughness have an impact on the visual appearance
but have no effect on glare in the Radiance model.

> Glass Frit – Composed of: Clear glass, 60% coverage white frit,  
> clear glass, 100% coverage white frit. From Window 6, I estimate  
> the solar reflectance of the system to be around 25-35%.
>
> Typle:               Metal ??? (Does the frit have specular and  
> diffuse reflection of light?)
>
Why don't you start with a glass material? If the frit is on the inside
you have at least one surface that will produce specular reflections
and might cause glare. A glass material would simulate that to some
degree. You can simulate the colour and transmittance with a trans
material behind the glass.
> Colour:             (1.0,1.0, 1.0)
>
> Specularity:       ????? (Clean polished glass)
>
> Roughness:      0.00
>

If you are interested in glare from reflected sunlight you should also
consider a 'mirror' material to trace the sun position more accurately.


Regards,
Thomas
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