A general lighting service (GLS) lamp is a light bulb that has an ANS/IEC base, but is not a specialty base lamp, and provides omnidirectional lighting. GLS light bulbs are generally household lamps that possess a common bulb shape of certain dimensions. The shapes and sizes of GLS lamps are designated by a letter (or letters) followed by a number. The letter indicates the shape of an incandescent bulb and the number is the diameter of the incandescent bulb. The most common GLS bulb shape is the A (Arbitrary) type. A-type light bulbs, e.g. A19 (A60) bulbs which have an E26/E27 medium Edison screw base or a B22d bayonet cap, are particularly prevalent in residential lighting. General service lamps also include reflector lamps that are not a specialty base lamp. GLS light bulbs serve residential light output needs broadly across a lumen package from 310 to 2600 lumens. These light bulbs are primarily used in table lamps, floor lamps, wall lights, ceiling lights, pendant lights and other household luminaires. The shapes and sizes of compact fluorescent lamps do not follow the footprint of GLS incandescent bulbs, although GLS CFL bulbs are made to be direct replacements for incandescent bulbs. General service LED lamps are typically designed with a shape and size similar to GLS incandescent bulbs.
