[Radiance-general] transmission/transmissivity

[Thomas Bleicher]

Hi Alexis.

On Thu, Nov 18, 2010 at 10:56 AM, alexis Loubeyre
<aloubeyre2 at hotmail.com> wrote:
> Hi everyone

> 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
> 0
> 0
> 3 0.65 0.65 0.65

That is correct. The change from transmittance to transmissivity
accounts for internal reflections in the glass. Please note that
strictly speaking this formula should be applied to a single sheet
of glass. If you want to model a double glazing unit the glass
material does not properly represent the angular dependency
of the light transmission. To accurately model this you should
use a tool like Window which allows you to export a description
of the glazing for Radiance.

> Other type, other question:
>
> for a mirror, what is the default specularity if I define default mirror
> with this function:
>
> void mirror window
> 0
> 0
> 3 0.965 0.965 0.965

The mirror material in Radiance does not represent a totally
reflecting surface as in real world. It is used to accurately represent
a reflection of a light source (like the sun) in a scene.

Regards
Thomas