[Radiance-general] virtual light sources with mirror & diffuse component

[Lars O. Grobe]

Hi all,

I am currently setting up a scene where I need the mirror modifier to
create virtual light sources. This mirror will stand for a metal sheet
with high specularity - but also some diffuse reflectance. First it
seams to be obvious, but the more I think about it the less sure I am
about it.

I defined a mirror material referencing a metal material, which includes
both the absolute reflectance and the specularity.

Example:

void metal mySheetMetal
0
0
5 .9 .9 .9 .8 0

That should lead to a specular reflectance of .9 * .8 = .72

(Typically, one would know the specular and absolute reflectance from
measurements and have to calculate the specularity from it - the other
way around.)

Is it this specular reflectance value of .72 that I have to use in my
mirror materials definition? Like

void mirror mySheetMirror
1 mySheetMetal
0
3 .72 .72 .72

My understanding is that the virtual source should have the value of the
original source times the specular reflectance, while for all rays not
hitting the sheet at an angle leading to the source in mirror direction
would lead to ambient sampling according to the metal definition.

Is this correct, do the metal and the mirror material match each other
in my example?

Cheers, Lars.