How ies2rad converts the geometry of luminaire

Hi everyone,

I am new to Radiance and when I exercise the ies2rad command, I am confused about geometry in .rad file generated by ies2rad.

The description of ies2rad in man1all.pdf shows that:
“The light source geometry will always be centered at the origin aimed in the negative Z direction, with the 0 degree plane along the X axis. (Note, this means that the IES “width” is actually along the Y axis, while “length” corresponds to the X axis.)”

In my ies file, it shows as follows and means that the length is 1.268, width is 0.158 and height is 0.050.

1 4874 1.0 73 37 1 2 1.268 0.158 0.050

So, according to the description of ies2rad, for the geometry of the luminaire, the x=1.268, y=0.158 and z=0.05. But in the geometry in .rad file generated by ies2rad, it shows as follows which means that x=0.158, y=1.268 and z=0.050. This makes me confused. Am I getting it right?

‘void’ brightdata ‘erco_dist’
5 boxcorr ‘erco.dat’ src_phi4 src_theta
4 1 0.158 1.268 0.05



Going by the code in ray/src/ies2rad.c, we assume the dimensions in the IES file are given in the order “width, length, height” and this comports with the output and explanation in the ies2rad man page. Perhaps @R_Fritz can confirm, as he’s more up-to-date on this format.


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Hi Greg,

Thanks a lot for your assistance.

With your suggestion, I read the ies2rad.c file. Because of my poor knowledge of Linux, I am still confused. Hope @R_Fritz could have time to confirm this.



Unfortunately, the IES LM-63 file format is written up in a document that isn’t free, so I can’t point you to the standard and it’s pretty obscure anyway, but Greg is correct; the order in the IES LM-63 file format is width, length, height. In the type C coordinate system that your IES file uses width is mapped to x, length is mapped to y, and height, of course, is mapped to z.

To look at your luminaire, use ltview; that will show you the luminaire looking towards the positive y direction. In general, looking at your luminaire is a good idea; it’s discouragingly easy to orient them wrongly.

If you really want to know more about LM-63, look here, but that’s not complete, and the details are finicky.

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Hi Randolph,

Thank you very much for your reply. It helps me a lot to understand the order of the dimensions of the luminaire. I appreciate it.


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