Glass is used to model transparent materials. Define the R, G, B transmissivity values (glass is a special case of dielectric with a refractive index fixed at 1.52 and all that needs to be defined is the transmission at normal incidence). The properties of glass are commonly defined in terms of the transmittance (by glazing manufacturers), to convert to transmissivity use the following equation -
transmissivity = (sqrt(a+4*sq(b*Tn))-c)/(d*Tn)
where Tn = transmittance,
a = 0.8402528435,
b = 0.042579995,
c = 0.916653006,
d = 0.00362611194
We have also found it impossible to get RGB data from glazing manufacturers, who will only quote a single transmittance value (even for tinted glass). We suggest for illuminance images this single value is used for each of the R, G and B values. For luminance images make minor adjustments to the relevant colour e.g. for a green glass increase the G value and decrease the R and B.
