[Radiance-general] ies2rad calculation

[Greg Ward]

Hi Rob,

The color values in the lamp.tab file are in CIE x & y plus depreciation factor (Y).  You can't just multiply this as if it is RGB.  You would have to convert to Radiance RGB first using src/cal/cal/xyz_rgb.cal like so:

rcalc -f xyz_rgb.cal -e 'myX=myx/myy*myY;myZ=(1-myx-myy)/myy*myY' -e 'myx=$1;myy=$2;myY=$3' \
	-e '$1=R(myX,myY,myZ);$2=G(myX,myY,myZ);$3=B(myX,myY,myZ)'

You would then input the xyY values from the lamp.tab file on stdin.  When I do this for your example, I get:

0.907836401	0.863244138	0.476356636

As you can see, these are exactly the RGB values that appear in the file.

Best,
-Greg

> From: Robert Franke <robertfranke at gmx.de>
> Date: July 25, 2012 4:50:09 PM PDT
> 
> Hi,
> 
> I try to understand how the ies2rad programm works, but I don't get it. The calculation of the three color channels in the description of material light  is unclear.
> 
> the lamp color (fluorescent ) is .373 .385 .85
> http://www.radiance-online.org/cgi-bin/viewcvs.cgi/ray/src/cv/lamp.tab?revision=2.3&view=markup
> 
> lamp radiance for every channel = lumens/area/(WHTEFFICACY*PI) * lampcolor
> area = 4*PI*r^2
> WHTEFFICACY = 179
> http://www.radiance-online.org/cgi-bin/viewcvs.cgi/ray/src/cv/lampcolor.c?revision=2.10&view=markup
> 
> This value 1.27324e+06 from my example is the inverse projected area of the sphere (1/(PI*r^2))
> 
> But where are this 0.907945 0.863233 0.476189 values from? This calculation (lumens/area/(WHTEFFICACY*PI) * lampcolor) doesn't match.
> 
> This is my example:
> 
> ies2rad -dm -t fluorescent Test.ies
> 
> IES-file
> -----------------------------------------------------------------
> IESNA91
> [MANUFAC]
> [LUMCAT] 2010_02
> [LUMINAIRE]
> [LAMP] Testlamp 1.000 lm 100W lamp*ballast factor = 1
> TILT=NONE
> 1 1000 1 131 360 1 2 0 0 0
> 1 1 100 ....
> .... .... ....
> 
> Output Data
> --------------------------------------------------------------------
> void brightdata Test_br
> 5 corr Test.dat source.cal src_phi src_theta
> 0
> 1 1.27324e+06
> 
> Test_br light Test_light
> 0
> 0
> 3 0.907945 0.863233 0.476189
> 
> Test_light sphere Test.s
> 0
> 0
> 4 0 0 0 0.0005
> ------------------------------------------------------------------------
> Thanks,
> Rob