[Radiance-general] Accurate definition of trans material

[Greg Ward]

I just wanted to confirm that the term "transmissivity" is used 
incorrectly on page 325 of "Rendering with Radiance."  It should be 
diffuse transmittance (a.k.a. "transmission coefficient") rather than 
transmissivity.  However, the equations for these values are correct.  
The term transmissivity is used properly in relation to the "glass" 
material type as given in the trans.cal code on page 238.

Google pointed me to these terms better defined on Schorsch's website:

	http://www.schorsch.com/kbase/glossary/transmittance.html

For further information, you can also refer to the document that I 
believe Pillo is referring to:

	http://radsite.lbl.gov/radiance/refer/materials.pdf

-Greg