How to describe a diffuse illuminating pane?

Dear group,

A quick question.
Which material can be used to describe a diffuse illuminating pane, cf. (hvælvet opal polycarbonat)?

Best regards

Per Haugaard

Hi Per!

This is a translucent, diffusing panel. There have been lots of discussions on this on the mailing list, as well as a bunch of presentations on workshops and even papers. The basic answer would be - use the trans material in Radiance.

However, the material model for trans is very generic, while translucent panels are made applying very different approaches. There is volume scattering, scattering by etching / sanding / ... a surface (outer or inner), laminating films on or in between panes, ... and all show different characteristics. In your case, it is probably volume scattering, so I would guess reflection to have a strong specular peak due to the clear, smooth surface, with a strong diffuse component from light scattered back, and probably a nice diffuse transmission. However, it is difficult to know before having any data on it. Can you see a light source through it, when holding it in fron of e.g. a strong lamp? Or does the brightness appear more or less flat? Peter is offering measurements using his goniophotometer, as well as others do. Christoph Reinhart described modeling a translucent panel in his paper:

Reinhart C F, Andersen M, "Development and validation of a Radiance model for a translucent panel", Energy and Buildings 38:7 pp. 890-904, 2006

which can be found at EPFL:

and presented on a workshop:

So a wide field to work on... Cheers, Lars.