[Radiance-general] Glass transmittance value

[Thomas Bleicher]

On 20 Nov 2007, at 10:36, Nicolas Roy wrote:

>
> Hi,
>
> I have a question concerning the definition of "glass" material. I  
> am trying
> to determine the transmittance of a window pane using spectrum  
> measurements.
>
> I have derived the following values for rgb (0.78, 0.85, 0.80).
>
> -Are those values determining transmittance or transmissivity?

Radiance expects transmissivity

> -Can the transmittance be derived using the formula  Tn = 0.265r +  
> 0.67g + 0.065b ?

No. The formula is

Tn = (sqrt(0.8402529435+0.0072522239*t*t) - 0.9166530661) /  
0.0036261119 / t

where t = transmittance and Tn = Transmissivity

Sorry for the format. I have copied it from a python script. Best  
thing I could
do in plain text.

I have a PDF document where this is further detailed. I just can't  
find it or
it's source on the web.

Regards,
Thomas