The compact fluorescent light bulb or lamp is a type of fluorescent lamp generally designed as a replacement for incandescent or halogen lamps. There are two major types of compact fluorescent lamp, screw-in and plug-in.
Screw in lamps are self-ballasted and can generally be placed in an existing screw socket without any additional equipment, plug-in bulbs require a ballast and a socket that corresponds to their specific base configuration. These are also sometimes referred to as integrated (screw base) and non-integrated (plug base).
Both come in a wide variety of wattages, sizes, color temperatures, and base types, and they are known primarily for their efficiency, long life, low cost, and ease of upgrading.
Both are gas-discharge lamps that use electricity emitted from cathodes to excite mercury vapor contained within the glass envelope, using a process known as inelastic scattering.
Phosphors and a noble gas such as argon are also contained within the glass envelope.
The mercury atoms produce ultraviolet (UV) light, which in turn causes the phosphors in the lamp to fluoresce or glow, producing visible light.