This economical dual bulb rain light offers redundancy: Even if one bulb burns out, the other will still work. Getting a black flag for a burnt-out rain light while leading a race is not our idea of fun. Two common #193 wedge-base automotive bulbs are included. The single wire design requires one of the mounting bolts to be grounded. A drain hole is provided so be sure to mount it in the correct orientation. The size is approximately 4 inches wide by 2 inches high. A rubberized gasket is provided.