[Radiance-general] Radiance and Lumen Micro Differences

[Martin Moeck]

John: 
 
I agree in general. I was thinking about complex museums with 2000 m2 ands lots of windows and mullions when I recommended my parameters. That's just the museum work that I am exposed to. But ever since 1990, we did tests at Siemens Lighting and it was always the same story: 5 -6 ambient bounces will get you there, even for simpler rooms. I have never found exceptions. 
 
Regards
 
Martin

	-----Original Message----- 
	From: John Mardaljevic [mailto:jm at dmu.ac.uk] 
	Sent: Mon 9/27/2004 11:47 AM 
	To: radiance-general at radiance-online.org 
	Cc: 
	Subject: [Radiance-general] Radiance and Lumen Micro Differences
	
	

	Martin,
	
	> In general, Radiance is more accurate than other programs if you make
	> extensive use of small patches with mkillum, set the -av parameter to a
	> reasonable value, and use the following parameters:
	> -ab 5
	> -ad 2048 or higher
	> -as 1024
	> -ar 5000
	> -ds .05
	
	> If you use -ab 1 instead of 5, your values are typically half of what they
	> should be. If you use -ab 3, they might be 30% too low.
	
	That ar setting is rather on the high side.  Also, the high accuracy
	that was achieved with the BRE-IDMP dataset relied only on the ambient
	calculation - no mkillum.  Some tests I carried out at the time (95-97)
	showed that accurate pure ambient tended to be faster than comparably
	accurate mkillum.  For both cases the parameters were gradually refined
	until the predictions converged to the measured values (method described
	in Chap 6 of RwR).  Radiance has changed a bit in the meantime, but I'd
	wager that pure ambient is still an effective way to achieve high accuracy.
	And maybe even more efficient too.  Perhaps I should repeat the tests using
	the latest version - but don't hold your breath just yet.
	In any case, I'd stick with the method of testing for convergence (Ch 6 RwR).
	The "optimum" parameter combination will depend on the scene, and convergence
	testing by progressive refinement is the quickest way to get there.
	It's the most reliable method too.
	
	-John
	
	-----------------------------------------------
	Dr. John Mardaljevic                    
	Senior Research Fellow
	Institute of Energy and Sustainable Development
	De Montfort University
	The Gateway
	Leicester
	LE1 9BH, UK
	+44 (0) 116 257 7972  
	+44 (0) 116 257 7981 (fax)
	
	jm at dmu.ac.uk  
	http://www.iesd.dmu.ac.uk/~jm
	
	
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