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How did you know about the light type "infinitesample"? 

I had to know the difference between infinite and distance light. So I looked into the source.

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How is it different from "infinite"? (Not Poser infinite, I mean the Lux light type.)

"infinite" in Lux is exactly what it is in Poser .

"infinitesample" is using the image like a "skyglobe" does. Additionally the same image is used to lit the scene. The difference here between Poser and Lux: For IBL in Poser only a small image is required. A skyglobe needs a very large one.

Adding a texture to an infinite light should give the same effect as in Poser (with small probes).

I've not mutch time at the moment, so I'm not able to test so mutch. I don't know yet what exactly the difference between distance and infinite light is.

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