[Radiance-general] useage of the dielectric material type

[Lars O. Grobe]

Hi all,

while it is one of the most fundamental material types in Radiance, dielectric is hardly used in simulations with Radiance as far as I know. I once or twice had to use it, but never for critical parts of a model.

Now, I need to find the irradiance in (!) a glass pane on the second surface S2 in this simple sketch:

|        |
|        |
| o      |    * source
| sensor |
|        |

S2      S1

The glass material applied to a flat surface through S1 obviously does not work here, as it includes reflection at S2 into the plane through S1. That would lead to an underestimate of about 4% at normal incidence. What I did is to model S1 as a dielectric, S2 as plastic, and ran the rtrace command with the -i switch, location as marked by the o-letter in the sketch and the view vector towards S2.

- My first question - is this a valid model in Radiance, with a volume having a dielectric interface on one, a plastic surface on the other side?

- Second question, can I expect rtrace to calculate a valid irradiance reading under these circumstances?

- Third question, and that is funny - how do I find the transmissivity parameters for a glass, as dielectric would expect them, if I have transmission T measured?

If someone here could share some insight how to find a valid dielectric description from a typical transmission measurement for the visible spectrum, that would be of great help for me....

Cheers and TIA,
Lars.
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