Quote - That is Image Based Lighting (IBL) where the surrounding mesh is used to calculate the quality and intensity of light based on the image attached to it. Using a cube to enclose the scene is almost the opposite. It does not, of course, a source of light; it limits the calculations required in tracing the light from the mesh(es) that are the source of light inside it. You may also have parts of your scene model outside the cube, those that will not be seen, and calculations will not be wasted on those parts. Yes, the IBL sphere itself would be too large for that purpose.

I could be wrong, but I believe Paolo said at some point that the IBL sphere isn't actually exported to Lux. It's just kinda there to help line up your IBL image. It'd be easy to try and see, as if it does, it'll be in the material section. :-)

Just for reference, I use IBL's almost exclusively for all my pictures, as it does add one big, colored light if you use the image with it. It can also be run without an image in the slot. Doing it this way--for me--adds a light that doesn't bog down big render scenes nearly as much as a slew of mesh lights. Granted, you don't get all the pretty shadows like you do with a mesh light, but its fast! I pair this with setting the render to 'Exterior'.

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