[Radiance-general] Re: Converting Kelvin to cxy

[Greg Ward]

Hi Iebele,

Actually, white would be "cxy 0.3333 0.3333", so the values you are  
getting are actually becoming redder as the temperature decreases, as  
expected.

There is nothing wrong with this method for computing CIE (x,y) from  
CCT -- it's probably best.  You can check against the other  
approximation, which is a table-based lookup in src/cal/cal/ 
blackbody.cal.  Just load this file into icalc or rcalc and evaluate  
the cct_x(kelvin) and cct_y(kelvin) with the same argument.

Best,
-Greg

> From: iebele <info at iebele.nl>
> Date: November 5, 2007 1:40:42 AM MST
>
> Hi there
>
> I try to convert different color temperatures into cie xy values  
> for use in lamptab.
> The script below is meant to convert degrees Kelving to cxy values,  
> for use in the lamp.tab file like this :
> /2800K/         0.4519 0.4086         1.0
> /2150K/         0.5108 0.4150         1.0
> The result is a bit strange, since the lower the kelvin value, the  
> more white my resulting lampcolor gets.
>
> Any suggestions?
>
> -Iebele
>
>
> #!/bin/csh
>
> if ( $#argv < 1 ) then
> echo "Usage $0 KELVIN "
> echo "Convert degrees Kelvin to spectral values and cie-xy "
> endif
>
> echo "cct $1"  > .Kelvin.tmp
> echo ""
> echo "spectral values of $1 K source:"
> mgfilt c,cspec .Kelvin.tmp
> echo ""
> echo "cie xy values of $1 K source:"
> mgfilt c,cxy .Kelvin.tmp
> echo ""