[Radiance-general] Modeling an oil lamp source

[steve michel]

Hi Greg,

I had a look at blackbody.cal can you guide us as to how the kelvin parameter is passed to this cal function into a usable rgb value?

Color temperature is very useful stuff for designers (especially retail) but so poorly represented in most renderers. Any help there would be appreciated

-steve
S&J LTD



----------------------------------------
> Subject: Re: [Radiance-general] Modeling an oil lamp source
> Date: Tue, 22 Apr 2008 15:03:33 -0700
> To: radiance-general at radiance-online.org
> From: gregoryjward at gmail.com
> 
> Hi Lars,
> 
> This looks about right.  The value for blue is zero because it's  
> actually outside the Radiance color gamut.  If you don't want to use  
> a table next time, the conversion from color temperature to CIE (x,y)  
> is provided in src/cal/cal/blackbody.cal.
> 
> -Greg
> 
> P.S.  I'm still waiting on your scene description to sort out the  
> other problem with the long rpict start-up time.
> 
>> From: "Lars O. Grobe" 
>> Date: April 22, 2008 2:00:49 PM PDT
>>
>> Hi list,
>>
>> this is the first time I am using colored light sources, and I am  
>> sure that I make some mistakes. So for your amusement and in the  
>> hope someone enjoys to show me the worst of my misunderstandings, I  
>> post how I try to model a light source, which is to represent an  
>> oil lamp.
>>
>> I estimate a flame with 2cm diameter, 10 lumen,1900 K black body  
>> temperature.
>>
>> I derive rgb 1.00 0.23 0.00 from the color temperature. This is  
>> only for the chromacity, and to be honest I did not do the CIE  
>> transformations but looked up in a table for 1900K.
>>
>> I add a line to lamp.tab reading
>>
>> /oil lamp/	.54 .41 .95
>>
>> so that I can use lampcolor and reuse my guesses later.
>>
>> No I run lampcolor, for the lamp type I enter my freshly defined  
>> oild lamp, I use meters as length unit, to model the flame I use a  
>> sphere geometry, and I give my estimated 0.01m radius for the flame  
>> (resulting in a luminaire sphere of 2cm diameter). My guessed total  
>> luminous flux is 10 lumens, leading to:
>>
>> Lamp color (RGB) 28.93 8.62 0.0
>>
>> Does this make sense? Am I totally wrong? I would apply a light  
>> modifier created with these values to a 1cm radius sphere now.
>>
>> Thanks, CU, Lars.
> 
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org
> http://www.radiance-online.org/mailman/listinfo/radiance-general

_________________________________________________________________
Enter today for your chance to win $1000 a day—today until May 12th. Learn more at SignInAndWIN.ca
http://g.msn.ca/ca55/215