Fluorescent lamps use tubular glass bulbs of varying lengths and shapes. The most common fluorescent lamp, the F40T12, has a straight tubular bulb that is 12/8 inches in diameter and 48 inches long. Widths are available from the T-5 at 5/8 inches to the T17 at 17/8 inches. Similarly, lengths range from approximately 12 to 96 inches. The compact fluorescent lamps come in even shorter lengths.

"U" Bent Fluorescent lamps are essentially regular 40-watt lamps bent into a "U" shape. This configuration allows two or three 4-foot-long lamps to be used in a two-foot square fixture. It offers the further advantage of allowing wiring and lampholders to be installed at only one end of the fixture.