[Radiance-general] How to represent a glazed surface in radiance

[Greg Ward]

A regular piece of glass has about 4% front-surface reflection, so glazing a material (where you create a single dielectric interface) typically matches this 4%.  If the outer surface is smooth, which is the general reason you would glaze something, then you get nice highlights due to low scattering rather than the amount of light that is reflected.  The amount of light reflected also increases towards grazing due to Fresnel's law, which is modeled correctly by "metal" and "plastic" when the roughness is zero.

To get two dielectric surfaces, which would add to 8% or so as you suggest, you would need the coating to not quite meld with the underlayer.  This is what plastic wrap looks like on a surface, and is not generally what people go for when glazing ceramics, etc.

Cheers,
-Greg

> From: Christopher Rush <Christopher.Rush at arup.com>
> Subject: Re: [Radiance-general] How to represent a glazed surface in radiance
> Date: November 20, 2015 9:47:16 AM PST
> 
> Per,
> For a little extra clarity, when you say "glazed" are you talking about glazed surface such as glazed terra cotta or similar, such as the way you would use the term in reference to pottery? Or are you referring to "glazed" such as being framed and covered in glass, like an opaque back-painted glass wall?
> 
> Greg,
> If it were a glass with opaque paint on the back side, would you still say the 0.06 specularity would represent the mirror-like reflections from the smooth glass surface?
> 
> If it were glass with any type of reflective treatment it could obviously have higher specularity. What if the front face of the glass is 0.06 specularity but the wall behind the glass could also be high gloss paint and add another 0.06?
> 
> I'm probably getting beyond the level of what's possible to estimate without talking about specific materials. But maybe there's a little extra of the theory behind it to understand.