If you have to, the lights can easily be removed. I did this and then took my cell phone and took photos of the entire area, I was looking for CATV cables. As I recall joists were on 24 inch centers. No idea why the stud finder did not work, unless the rough finish interfered with its operation. The one I have does work on the rough walls, and I have had reasonable luck on ceilings.
Hope this helps.
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Pennsylvania, for 60+ years, most recently, Allentown, now TV. 
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