[Radiance-general] material trans and glass?

Christopher Rush Christopher.Rush at arup.com
Sun Dec 20 08:41:51 PST 2009

The formula I have to go from total transmission to transmissivity is





For trans definition from page 325-326 of Rendering with Radiance:



Cr,Cg,Cb are the diffuse reflectance in R,G,B channels, and Rd is the
photopic average of those.

Rs is reflected specularity (fraction reflected off first surface in
mirror fashion)

Sr is surface roughness similar to plastic

Td is diffuse transmissivity (fraction transmitted diffusely in a
scattering fashion)

Ts is fraction transmitted as a beam (like through clear glass, not


In reverse order, the parameters for trans can be calculated as:


A7=Ts / (Td + Ts)

A6=(Td + Ts) / ( Rd + Td + Ts)



A3=Cb / ( (1-Rs)*(1-A6) )

A2=Cg / ( (1-Rs)*(1-A6) )

A1=Cr / ( (1-Rs)*(1-A6) )


Then the -st setting for rpict or rtrace should be:


St=A6*A7*( 1 - photopic average(A1,A2,A3) * A4 )



From: radiance-general-bounces at radiance-online.org
[mailto:radiance-general-bounces at radiance-online.org] On Behalf Of
Victor Li
Sent: Sunday, December 20, 2009 3:24 AM
To: Radiance general discussion
Subject: Re: [Radiance-general] material trans and glass?


Does anyone tell me the definition and difference between Transmisivity
and Transmittance? 

What is the definition of the frist 3 numbers and the second to last
number of trans definitions?

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