[Radiance-general] How to simulate an artificial sun

[Greg Ward]

Hi Kai,

Is the 20,000 lux measured at the source or at the receiving surface?

You are best off using the "source" type with a 1.5-degree solid  
angle, even though your source is not infinitely distant.  Do you  
care very much about the fall-off at the edges of your model?  You  
could create an aperture that passes the infinitely distant source --  
essentially a large opaque ring with a 70 cm hole in the appropriate  
place.  Does the behavior of the light source have to precisely  
match, or is an approximation such as this good enough?

Does this make sense?
-Greg

> From: "Kai Babetzki" <babetzki at transsolar.com>
> Date: May 29, 2009 9:32:26 AM PDT
>
> Dear Radiance Community,
> I'm trying to compare measurements done in an artificial sky with
> radiance simulations. The problem I'm currently facing is how to  
> model a
> lamp with a diameter of 70 centimeter that produces 20000 lux with an
> aperture of 1.5° (nearly parallel light) in Radiance?
>
> Will be the only possibility to measure the existing lamp in a
> photogoniometer and use the ies format data files? Or are there other
> and maybe easier ways to simulate such an artificial sun lamp in
> Radiance? Some quick and dirty way would be nice!
>
> Kind regards,
> Kai