I know that wraparound fixtures have metal spacers formed into the top of the fixture to keep it off the mounting surface (approx 1/2-3/4"?). I intend to install some fluorescent fixtures on a drywall ceiling in a garage-turned-barber shop. However, I seem to remember reading something about commercially available 1 1/2" spacers to mount fluorescent fixtures on combustible materials. For that matter, is a drywall ceiling even a concern for this installation?
