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.
Although compact fluorescent lamps are considered to be a fairly recent technology, this bulb type was actually over 100 years in the making. Circline and U-bent bulbs were both created to reduce the overall length of fluorescent bulbs and were precursors to the CFL as it is known today.
The modern CFL was invented by Edward Hammer, an engineer at General Electric, but was not produced at the time due to high production costs. In 1980, Philips became the first manufacturer to mass-produce a compact fluorescent bulb with a screw-in base.