A light socket is a fixture that connects a light bulb to a power source. There are a number of different types of sockets, with specific fittings for various types and sizes of light bulb but all function on the same principle. The socket is connected to a source of electricity, often an electrical wire or a battery, and contains two different contact points, which provide electric current to the bulb, causing it to illuminate, when it is secured in the socket.

One of the most common types of light socket is in the form of a shallow, threaded, metal cylinder. A lightbulb with corresponding threading can be screwed into this type of light socket. The metal along the edge of the socket forms one contact point and a metal piece at the bottom of the socket forms the other. The electrical current flows into the light bulb only when it is screwed all the way inside this type of socket. These types of sockets are frequently used with standard incandescent bulbs, though energy efficient bulbs are also made to fit these sockets.

Light emitting diodes (LEDs) and florescent light bulbs also need to be plugged into a light socket in order to light up. Specifically shaped sockets are required for these bulbs, however, and often allow the bulbs to snap into place. Long, overhead florescent tubes will often use sockets with one contact point at each end of the bulb. LEDs often plug into their sockets with two metal prongs at the base of the bulb.

A light socket is designed to handle a certain wattage and a certain voltage. Bulbs that require a wattage higher than the capacity of the socket can burn out the socket, which can cause a fire. When purchasing a replacement bulb, it is important to look at the specifications of the socket and make sure that the light bulb falls within the acceptable range.

The size of a light socket is another important consideration with choosing a replacement light bulb. Many sockets are built to a standard size that accommodates many different bulbs, but there are sockets that are larger or smaller and require a bulb that fits properly. Forcing a bulb in to a socket that it is not designed to fit, regardless of the wattage of the bulb, can cause the two components to malfunction.