This is from the sIBL site, right?

While that can be used (as in better than nothing) it was made rather poorly. The HDR has no values above LDR maximum, which means it isn't HDR at all. The person who made it thinks that calling a file HDR makes it high dynamic range by virtue of the name and format alone. It doesn't. HDR files that have no values above 1.0 are not "high" - they are just files that could have been "high".

I would also have expected the file Milkyway_BG.jpg to be higher resolution, but it isn't.

You don't need the ibl file.

For the sphere, you can use either Milkyway_BG.jpg or Milkyway_small.hdr - you're going to get the same result, since they contain the same information. They are encoded differently but that makes no difference. Use either of these.

The file Milkyway_Light.hdr is not the same image as the others. It's got artifical splotches of light to make the scene lighting be brighter. It's no good for looking at and no good for reflections, either. Personally, I'd throw it away.

 

 

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)