Edison Screw Bases
The light socket is a universal icon of electrical power, and nearly everyone in North America who has ever changed a light bulb has encountered this style of lamp base. While other methods of connecting lamps to their lamp holders do exist the Edison screw base is the most common.
In an attempt to make newer bulb technologies still work with older lighting systems that utilize the popular Edison screw base, many new CFL and LED bulbs are available to replace older less efficient incandescent bulbs. These energy-efficient lamps are designed to run on standard 120V systems and will screw into the lamp holder in the same fashion as the lamps they replace.
Not all lamps work with the Edison Screw base. Bayonet style bases are popular with low voltage halogen lamps and some florescent pot-light fixtures utilize specialized connectors that will reject incorrectly sized CFL bulbs.