AW: Re: [Radiance-general] How to simulate an artificial sun

[Kai Babetzki]

Hi Greg,
thanks a lot for answer. That's exactly the solution I was looking for. 
I don't care to much about the fall-off at the edges of my model. This 
approximation meets all my expectations.

Kind regards,
Kai 

-----Ursprüngliche Nachricht-----
Von: Greg Ward [mailto:gward at lmi.net] 
Gesendet: Freitag, 29. Mai 2009 19:41
An: Radiance general discussion
Betreff: Re: [Radiance-general] How to simulate an artificial sun

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

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