[Radiance-general] transmission/transmissivity

Christopher Rush Christopher.Rush at arup.com
Thu Nov 18 08:16:29 PST 2010

Regarding the glass definition, what you wrote makes sense although I didn't check the math.

Regarding mirror, it is fully specular - all of the 0.965 reflection in your definition below would be reflected in a purely specular manner.

Sent: Thursday, November 18, 2010 10:57 AM
To: radiance-general at radiance-online.org
Subject: RE: [Radiance-general] transmission/transmissivity

Hi everyone

In radiance manual, when you want to create a glass material, we use this function:

void glass id
3 rtn gtn btn

where tn is the transmissivity which comes from this formula:

tn = (sqrt(.8402528435+.0072522239*Tn*Tn)-.9166530661)/.0036261119/Tn

where Tn is the transmittance.

For example, if i have light transmission for a window equal to 60% (given by a manufacturer), do i have to calculate tn with Tn =0.6

and then put my results in the function, so with this example we'll have: tn = 0.65 with Tn = 0.6?

void glass id
3 0.65 0.65 0.65

Other type, other question:

for a mirror, what is the default specularity if I define default mirror with this function:

void mirror window
3 0.965 0.965 0.965

Thank's a lot for your help.



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