[Radiance-general] METAL material values

[Lars O. Grobe]

> Then, my question is: what is the difference between "Total Reflection %"
> and "Specular Reflectivity %", and how does this translate in the METAL
> material values?

Hm, I hope I do not write something wrong now...

The total reflection is the relation of energy reflected to the energy
that is hitting the surface. 100 hit the surface, so, if total
reflectivity is 95%, 95 leave it.

Specular reflectivity is the part of what is reflected that is leaving
the surface in a directed manner. So to go on with our example, is 95%
was the total reflection, and the specular reflectivity is 90%, of the
100 hitting the surface 0.9*95=85.5 leave the surface as specular
reflection. That also means that the remaining 0.1*95=9.5 leave it as
diffuse.

My total unitless numbers would all translate into radiance Watt / (sr *
m2).

> My other question is still about the value ranges:
> 
> What are the maximum values for "specularity" and "roughness". I would like
> to confirm if the maximum value for specularity is 1.0 (or maybe more?) and
> if the maximum value for roughness is 0.5 (although I have found in some web
> links that roughness values greater than 0.2 are not realistic)

Specularity cannot be more then 1, as you cannot have more energy
reflected as specular then energy reflected in total. If you replace the
maximum 1.0 by 100% you will understand.

As far as I know you are right about roughness, but it is difficult to
estimate this parameter, and I treat it more as a visual effect...

CU Lars.
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