Compact fluorescent lamps (CFLs) offer significantly greater efficacy and longer life than incandescent bulbs. CFLs and circline fluorescent bulbs are diffuse, nondirectional light sources that are suitable for ambient lighting and task lighting. CFLs are available with a wide variety of color rendering properties (CRI) and correlated color temperatures (CCT).
CFLs are available with different bases, including the screwbase, 2- and 4-pin base, and GU24 "twist and lock" base. Most circline fluorescent bulbs are pin-based. All fluorescent bulbs require ballasts to provide the starting voltage and limit the electrical current during bulb operation. Screwbase CFLs and GU24 CFLs have integrated ballasts, which are permanently attached to the base of the bulb. CFLs with 2- and 4-pin bases require separate ballasts, and are more common in commercial and industrial settings.
Screwbase CFLs are available in a wide variety of styles including a bare spiral and covered A-lamp, globe, capsule, reflector, and candelabra. The bare spiral is the most commonly used. Covered A-lamp, globe and capsule CFLs have built-in diffusers and are suitable when the fixture does not hide the bulb from view (e.g., downlight pendant over a table); the diffuser enclosure may be glass or breakage-resistant plastic. CFL reflectors are designed to aim light in a particular direction, and are suitable for task lighting or for creating a soft wash of light. CFL candelabras, also known as candle CFLs, are available for decorative lighting, such as in wall sconces.
Screwbase CFLs screw directly into medium-base bulb sockets used by incandescent bulbs, however, screwbase CFLs are heavier and may be larger than incandescent bulbs. Check to see if plug-in fixtures would become unstable due to the heavier weight of the screwbase CFL. It may be necessary to install a harp extender to raise a table bulb shade to make more room for the CFL. When relamping incandescent recessed downlights, other technologies, such as LEDs, are more suitable than CFLs.
Some CFLs and circline fluorescent bulbs are dimmable, but this must be indicated on the package by the manufacturer. For use with a three-way fixture, look for bulbs marked "three-way" to provide a high, medium, or low output. Circline fluorescent bulbs require a compatible dimmable ballast.