[Radiance-general] Radiance and Optics

[Aris Tsangrassoulis]

Dear Robert,

I 'm using frequently Optics software to get data for radiance window
modelling. You can also use WINDOW 4.1 instead. I think that the BRTDfunc
description of the glazing gives values for transmittance (and reflectance)
instead of transmissivity (glass material). Naturally there are two
descriptions for front and back surfaces of the window since properties are
quite different. The description in your example deals only with direct
normal transmittance hence it does not take into account the transmittance
angular behavior of the glazing. This can be treated as follows: by using
for example  Window 4.1 you can calculate the transmittance in various
incidence angles. By using a polynomiac interpolation you can create a
function of transmittance versus angle of incidence (i.e. Rdot). In fact
this fucntion is a normalized function because each value is diveded by the
normal  transmittance. Thus is your BRTDfunc description you should add
glazing.cal function with modified transmittance and reflectance
accordingly.
I hope that this might help.

Aris Tsangrassoulis