Another thing to understand is that the exact lighting from inside a room is not easily discerned by a human looking at the effects of that lighting on a subject. It may be that you can just pick one of thousands of existing interiors and get lighting that is good enough to use with your background photo, which does NOT have to be on a sphere but rather can just be a rectangle.

Have a look here at https://www.flickr.com/search/?text=equirectangular%20indoor

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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)