[Radiance-general] 10k lux overcast sky implementation only yields 9177?

[Claus B. Madsen]

Hello Christian,


My suspicions concerning your problem go towards the fact that there 
apparently are many ways to convert from RGB radiances to Lux (using 
slightly different RGB weights) ... moreover it is my general experience 
that Radiance, when looking straight into a light source, produces 
radiances that are slightly less than the source radiance specified in 
the scene file. For example when I point the "camera" straight into an 
RGB = 1 W/(m^2 * sr) sky dome I get radiances of 0.9941 (although that 
may be due to finite precision in the .hdr file format).

Seeing that you are from Denmark (as well) I took the liberty to call 
you on the phone (your company switchboard informed me you were away on 
travel) ... if you feel like discussing some of these things (not that I 
necessarily have the answer to your problem) we can contact each other 
when you get back.


Best,
Claus


Christian Anker Hviid wrote:
> Hello Radiance users
>  
> I use gensky to create a 10k lux CIE standard overcast sky with the -B 
> command:
>  
> gensky 6 1 14 -B 55.866 -c -g 0.2
>  
> I use the following commands to generate a center line of daylight at 
> working height (.85m) in a room:
>  
> cnt 11 \
> | rcalc -e '$1=2;$2=$1/2+.5;$3=.85;$4=0;$5=0;$6=1' \
> | rtrace -I -dt 0.03 -ds 0.02 -ab 3 -aa .15 -ar 128 -ad 1024 -as 512 
> -h -w -oov scene.oct \
> | rcalc -e '$1=$2;$2=179*(.265*$4+.670*$5+.065*$6)' > lux.dat
>  
> But when I remove everything from the scene but the sky, I only get 
> approx 9177 lux on my centerline. According to theory I should be 
> getting approx 10000. What is wrong?
>  
> Thank you for your time.
>  
> Christian Hviid
> ------------------------------------------------------------------------
>
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