T12 light bulbs are fluorescent lamps that have a diameter of 12/8 inches (1.5 inches). They were widely used in commercial and industrial lighting applications, but have largely been replaced by T8 (1 inch diameter) and T5 (5/8 inch diameter) lamps. T12 lamps use magnetic ballasts, consume more energy than the newer lamps, and have a lower light output and efficiency. Due to these factors, T12 lamps are less common and being phased out in favor of more energy-efficient lighting options.