The length of a fluorescent light bulb is measured from the back of the socket on one end of the bulb to the back of the socket on the other end. The bulbs are labeled according to the diameter and the length. Linear tubes range in length from 6 to 96 inches and fit into slightly longer fixtures. The diameter of circular bulbs is often 8 or 9 inches.
The most common fluorescent light length is 4 feet. Bulbs of this length are the easiest to buy and handle. Often they are cheaper than bulbs of other lengths, and they last longer.
Other Size Fixtures
Tubes 8 feet long may fit into large rooms, but they aren’t often used. Two 4-foot fluorescent bulbs in fixtures mounted end-to-end provide the same light as an 8-foot bulb. Shorter bulbs with lengths of about 1, 2 or 3 feet are available in home supply stores. Custom bulbs are constructed to be any length up to 8 feet.
Standard fluorescent lights usually have a pin-based design to fit into fluorescent light fixtures. With compact fluorescent bulbs, the tube is twisted into a spiral shape. The screw base allows the bulb to be used in fixtures designed for incandescent lights. In residences, fluorescent lights provide illumination for kitchens, counters, cabinets, bathrooms and garages. For uniform light, all fixtures in a kitchen should be the same length. U-shaped fluorescent lights are often used as under-cabinet light fixtures.