Bases
 The base serves several functions. It connects the lamp bulb to the socket delivering power to the lamp and it physically supports the lamp in the fixture. The principal raw materials used in manufacturing bases are sheet brass or sheet aluminum and glass. Although bases come in some 30 different styles and sizes, the two general service lamps used most often are the medium-screw and mogul-screw.
Interestingly, the type of base and socket screw shell which Thomas Edison devised in 1879, has been used for over 70 years without any fundamental change. Since that time U.S. standards have been adopted for the popular miniature, candelabra, intermediate, medium, and mogul screw-thread types. Bases, along with their corresponding sockets are manufactured in accordance with these standards to ensure their safe and satisfactory use.
The most popular base used today is the metal screw base made of aluminum or brass. Sizes are determined by bulb size and current carrying capacity. For general lighting purposes, medium screw-type bases are most common. For higher wattages, greater than 300 watts, the mogul screw base is used. Some of the lower wattage lamps, particularly the indicator and decorative types, are made with candelabra or intermediate screw bases.
Prefocus bases are used where accurate positioning of the light source with respect to an optical system is required. Skirted bases are used when a large bulb neck simply isn't compatible with the desired base size.
 A medium bi-pin or mogul bipost base, usually used on high-wattage lamps, consists of two metal pins or posts embedded in a glass "cup" forming the end of the lamp bulb. Most screw and prefocus bases are attached to the bulb by means of a specially designed "basing cement." A variety of cements and application methods are used to meet the needs of different operating base temperatures.
  Fluorescent lamps utilize a variety of bases for connecting the lamp bulb to the fixture. Rapid Start and Preheat lamps typically use a bipin base. The medium bipin is available for T-12, T-10, and T-8 lamps. A miniature bipin base is available for smaller lamps. Single pin and recessed double contact bases are used in Slimline lamps, ranging from the T-8 to the T-12, and even T-17 lamps. Compact fluorescent lamps use a special two-pin base designed to fit into a small ballast outlet.
Some compact fluorescent lamps, with an integral ballast, use medium screw bases identical to those used on incandescent lamps; they are often used as direct replacements for existing incandescent lamps
    
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