Lamps are typically identified by a code such as F##T##, where F is for fluorescent, the first number indicates the power in watts (or where lamps can be operated at different power levels 12V and 24V, the length (L) in inches), the T indicates that the shape of the bulb is tubular, the last number is the diameter in eighths of an inch for US (sometimes in mm, rounded to the nearest millimetre for EU). Typical tube DIA are T12 or T38 (11/2" or 38.1mm) for residential bulbs with old magnetic ballasts, T8 or T26 (1" or 25.4mm) for commercial energy-saving lamps with electronic ballasts, and T5 or T16 (5/8" or 15.875mm) for very small lamps, which may even operate from a battery powered device