These 1.5" diameter lamps were the standard commercial and industrial fluorescent lamps for several decades. They are available in many lengths, including: 1, 2, 3, 4, 6, and 8 foot lengths, and are produced in many variations by numerous manufacturers. Two common versions of 4' T12 lamps are 40-watt lamps, and “energy-saver” 34-watt lamps.Energy-saver T12 lamps reduce energy consumption and light output by about 15%. Although T12 lamps are sometimes powered by electronic ballasts (lighting transformers), they are typically powered by less efficient magnetic ballasts.