[Radiance-general] Guidelines for trans Material

[Marcus Jacobs]

Dear Group

I am modeling a bathroom that will use translucent light fixtures similar to 
this:

http://www.homedepot.com/cmc_upload/HDUS/EN_US/asset/images/eplus/725916808877_3.jpg

I wish to accurately simulate the light distribution from the fixtures 
however I do not know where to begin as far as determining physically valid 
parameters for the trans material. Does anyone here know where I may obtain 
data for such light fixtures and how to correctly translate this data into 
Radiance?

I have some additional questions concerning the trans material type. In a 
Radiance reference manual, it is stated:

"Trans is a translucent material, similar to plastic. The transmissivity is 
the fraction of penetrating
light that travels all the way through the material. The transmitted 
specular component is the fraction of transmitted light that is not 
diffusely scattered. Transmitted and diffusely reflected light is modified 
by the material color. Translucent objects are infinitely thin."


First, should the transmissivity + transmitted specular component = 1 in 
order for the material to be physically correct? Also, since the transmitted 
specular component is the fraction of transmitted light that is not 
diffusely scattered, does this mean that this is apart of the direct 
calculation or is this too apart of the indirect calculation.


Thanks

Marcus