Edit the family, and under light source, change it to one of the "non-photometric" types.
The .ies file is probably causing some issues when rendering with mental ray.
I'm not sure that the high level of detail you are after is actually possible using Mental Ray inside of Revit.
Perhaps in 3dsMax Design this is possible--so I'm not sure all the extra effort in Revit is worth it.
Have you seen this: ???
This might be a good compromise for getting accurate lighting studies inside of Revit.
And, yes--I understand photometrics and .ies files.
Glad to hear it. We need more good content for Revit.
Let us know when you have some products up on Seek or a website.
If we like them, they just might get spec'd on one of our projects!
Thought I'd bump this thread to illuminate (heh, pun intended) some of the issues Revit has with absolute IES files.
The work around is to change the "initial lumens" value in the IES file from "-1" (meaning it's absolute) to the lumen value of the fixture.
In my example. I was using the Lithonia 2RTL2 LED light fixture and an absolute IES file (sounds like a terrible vodka) from Lithonia's website. Attached.
I also compared it to the standard version of this fixture, the 2RT5 with two, 14 watt, T5 fixtures at 3500 Kelvin. Also attached.
Here's the first go:
As you can see. The "absolute" IES file gave us our lovely rainbow we're used to seeing when rendering with absolute IES files in Revit. On the right is the traditional fluorescent IES file with it's initial lumen value set at 2400 (2 x 1200).
Then I read this little article to get a better understanding of the IES file format:
As you can see it explains where the "-1" goes in the IES file. Find it, and you'll be halfway there. So I changed the "-1" to the initial lumen value of the LED fixture of "3300" as stated in the IES file. I added "_AW" to the end of the file for my modified version. Attached.
Here are the results:
From left to right: Original LED ies file, modified LED ies file, and original fluorescent IES file.
FROM WHAT I HAVE OBSERVED. The light web appears to have remained intact allowing Revit to render. It will probably not be as accurate since I have monkied with something I do not fully understand (the IES file format).
However it appears this work-around succeeded.
AS OTHERS HAVE MENTIONED, I DO NOT USE REVIT AS A LIGHTING ANALYSIS TOOL! I only use it for rendering out images to put in promotional material or meetings with clients.
Currently, we use ElumTools and LightPro in our office to do accurate point-calcs. The former, ElumTools, being a brand new extension that uses the Revit API to link in AGI32s lighting calculation system for accurate point calcs. ElumTools does understand the absolute value and will produce accurately thrown light.
As always, with all work-arounds, YMMV. Finally, here is the light fixture family:
Just an update to this topic.
I've taked with Autodesk support.
This is a known issue that both the Revit and 3ds Max team are working on.
Both use the "Mental Ray" rendering engine. With Revit you have no choice but to use it, but in 3ds Max you can use "scanline" or w/e it's called. So if you want to render scenes with absolute IES files in 3ds Max -- use the 3ds Max engine.
But it's really all on the Mental Ray team's shoulders. It's their engine which doesn't like absolute IES files so we'll have to wait to hear from them. (I've emailed the Mental Ray team directly, but they haven't responded yet).