I use glass tops as well, partly to keep the fish from jumping and partly to control evaporation, as the tank is in the basement and too much dampness will grow mold on the walls. I alsy was afraid that if a fish splashed the lights when they were hot, they could shatter and I'd have broken glass all over my tank. Might be unlikely, but possible. I just went to the hardware store and had them cut pane glass to size for me, much cheaper than plexi.