Types of Lightbulb Bases

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Types of Lightbulb Bases
Edison screw base is one type of light bulb base. (Jupiterimages/Photos.com/Getty Images)

The base of the light bulb is the part that fits into the socket. This is the electrical connection point of the lamp. There are several types of sockets and bases. It is important that the light bulb matches the socket. Bases differ depending on the voltage and type of light, as LED, fluorescent and incandescent light bulbs all use different bases.

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Bayonet Base

A bayonet base is used for bayonet base sockets. The bayonet is frequently known as the B22d or the BC. It has two lugs at the bottom and is used on lamps and for low-voltage halogen lamps. The bayonet can also have three pins used for high-pressure mercury lamps and Fireglow lamps. The most common sizes are the 15mm diameter and the 22mm diameter. To fit this light bulb base in the socket you simple push the bulb in and twist.

Fluorescent Fittings

Fluorescent light bulbs, whether they are tubes or bulbs, will have pin fittings at the end. Two pin fitting lights will contain an integral starter and those with four pins will also have dimming controls. Fluorescent tubes will have pins on both ends of the tube.

Edison Screw Cap

The Edison screw cap is named after Thomas Edison, the inventor of the light bulb. The base has a screw threading, mostly a right-hand threading. There are two main disadvantages to this base, as it can be an electric shock hazard if the lamp is not wired properly or the plug is connected to a non-polarised outlet. It can also stop working if the bulb is screwed in too tight, as the centre contacts will become misaligned. There are several different sizes for the Edison screw cap, from 5mm to 40mm.

Wedge Base

The wedge base is used for small light bulbs. This is very similar to a two-pin base, except the two pins in the wedge base are the same wires that run through the interior of the light bulb. When electricity is applied the wires glow and produce light. The two wires extend straight out the bottom. They are then bent up the sides of the base. The wires then make a connection with the lamp base. This is called a wedge base because the base is made of plastic and shaped like a wedge with a smaller tip and wider top where the light bulb is. These bulbs can snap into place or are held in place due to compression. Wedge lights are used for landscaping or as automotive lights.

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