calculating transmissivity

Project Code : .

I am having trouble calculating the correct transmissity values to use
within Radiance.

The transmittance values i need to calculate from are 0.46 and 0.70. Can
someone please tell me what the corresponding transmissivity values will
be?
I am trying to use a formula from the Rayfront website, but I am getting
some strange results...

Thanks,
Ben Masters

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[email protected] wrote:

I am having trouble calculating the correct transmissity values to use
within Radiance.

The transmittance values i need to calculate from are 0.46 and 0.70. Can
someone please tell me what the corresponding transmissivity values will
be?
I am trying to use a formula from the Rayfront website, but I am getting
some strange results...

I'm assuming here that you're talking about the glass primitive.
The formula in ray.pdf is formatted in a slightly confusing way.
There's an unambiguous graphic version to be found here:

http://www.schorsch.com/rayfront/manual/dielectricdef.html#glass

-schorsch

···

--
Georg Mischler -- simulations developer -- schorsch at schorsch com
+schorsch.com+ -- lighting design tools -- http://www.schorsch.com/

[email protected] wrote:

Project Code : .

I am having trouble calculating the correct transmissity values to use
within Radiance.

The transmittance values i need to calculate from are 0.46 and 0.70. Can
someone please tell me what the corresponding transmissivity values will
be?
I am trying to use a formula from the Rayfront website, but I am getting
some strange results...

There is a .cal file in the UNIX distribution (in /src/cal/cal) of Radiance that you can use with the calc utility to easily compute these values. You type "calc /path/to/trans.cal" at the comand line, and feed it your transmission values (tn), and it spits out a transmissivity value:

% calc trans.cal (or full pathname if not in a PATH location)
tn(.88)
$1=0.958415435
tn(.57)
$2=0.621392084

Just keep on feedin' it values and recording the output, and hit control+D to quit when you're done.

···

----

      Rob Guglielmetti

e. [email protected]
w. www.rumblestrip.org