A-series light bulb

The A-series light bulb is the "classic" glass light bulb shape that has been the most commonly used type for general lighting service (GLS) applications since the early 20th century. It has a pear-like shape and is typically fitted to either an Edison screw or a bayonet cap base. The number that follows the "A" designation indicates the nominal major diameter of the bulb, either in one-eighth inch units in North America or in millimeters in the rest of the world.

Although A-shape bulbs historically used incandescent lighting technology, A-shaped compact fluorescent (CFL) and LED lamps are also commonly available.