ies2rad calculation

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
3 0.907945 0.863233 0.476189

Test_light sphere Test.s
0
4 0 0 0 0.0005
------------------------------------------------------------------------
Thanks,
Rob

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 <[email protected]>
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