IES lights - defined with or without fixture housing

Hello,
Are IES light files defined including the affect of the physical light fixture?

In other words - may I or should I - turn off the fixture object when rendering lighted scenes?

thanks, Jeff

HI @ibear88
I believe IES files are light source only - see here:
http://www.cgarena.com/freestuff/tutorials/max/ieslights/

HTH, Jakob

I contacted IES and here is what their education department had to say (I obtained their permission to reprint it here):

Jeff,

“IES” photometric data files (*.ies) can be either for a luminaire or just a light source. However, they are almost always for a complete luminaire; IES files for lamps alone are actually quite rare. This is because it’s pretty difficult to test a lamp alone; it needs some kind of other equipment in order to function.

Thus, the IES file for a recessed LED downlight includes the light source and the surrounding luminaire (reflector, lens if applicable, etc.). The IES file for a pole-mounted “acorn” luminaire includes the light source and the surrounding optical system. A luminaire is tested in the photometric lab as a complete unit. So the IES file applies to the complete unit.

Luminaires are tested in a photometric laboratory at a distance that causes them to effectively be a “point source.” This enables the resulting photometric data file (IES file) to be used at any distance in the model and calculations except very close to the receiving surfaces (which would be an unusual situation anyway). The IES file contains information on the physical dimensions of the light-emitting part of the luminaire (as seen from the outside), but not the entire luminaire. For example, the X-Y-Z dimensions of a 2x4 recessed troffer will be 2, 4, 0 if the dimensions are in feet. The 0 is because there is no depth to the light-emitting part of the luminaire (as seen from the outside); it’s just a flat lens. In the case of an industrial low-bay luminaire (with a reflector and a prismatic drop-lens), the dimensions might be 1.25, 1.25, 0.5. The X and Y are the diameter of the drop-lens (they’re the same because the drop-lens is circular), and the Z is the depth of the drop-lens.

It’s actually not a good idea to add something to the outside of your modeled luminaire, such as a house-side shield on a roadway luminaire. Because the luminaire isn’t a “point source” to that added object (it’s actually quite large from the perspective of that added object), the effect of the object on the distribution of light from the luminaire won’t be modeled correctly in the software.

I hope this helps. Let us know if you have any other questions.

Looking forward,

Dawn De Grazio, LC
Technical Editor, IES

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