Can a T5 lamp replace a T12 or T8 lamp?
T5 lamps cannot replace T12 or T8 lamps because of differences in physical and electrical characteristics. T5 lamps come in different lengths than T8 and T12 lamps. A nominal 4-foot T5 lamp is actually shorter than an equivalent T8 lamp [1149 millimeters (45.23 inches) in total]. Miniature bi-pin sockets fit T5 lamps, while T8 lamps need medium bi-pin sockets. These differences in dimension prevent T5 lamps from being used as replacements for T8 lamps (see What are T5 lamps?). T5 lamps need special ballasts to operate (see Do T5 lamps need special ballasts?).