Light bulbs come in a variety of shapes and sizes as well as wattage amounts. Light bulbs can be categorised by the shape of their bases (the part of the bulb that screws into a light socket), and the letter E before a number indicates the bulb's base type. E12 designates a particular type of light bulb base designed for specific types of lighting.
According to Harrington Lights, there are seven types of light bulb bases: E10, E11, E12, E14, E17, E26 and E39. Each base size fits a specific light socket or style of lighting fixture. E12 light bulbs are generally known as candelabra light bulbs.
The size of an E12 bulb's base is 12mm in diameter and, as such, will only fit light sockets that are the same diameter. The bulb itself is a short bulb just under two inches in height. The bulb is identifiable by its unique shape, bulging out slightly in the centre before getting more narrow at the top of the bulb (see the Resources section below for a link to view images of various E-sized light bulbs).
E12 light bulbs are commonly used with hanging chandeliers and small night lights. They can also be used in electric candles that are placed in a house's windows at night. They can be used in any lighting appliance that has a 12mm socket.
This type of light bulb is an incandescent light bulb. This type of light bulb contains a small tungsten-based wire in the centre that, when heated by electrical current, will produce light. The glass of the bulb itself prevents oxygen from entering the bulb structure, which would counteract the heating of the tungsten wire. The heating effect requires an oxygen-free environment to produce the glowing light.
The E12 bulb can fit into a socket that is 1 1/2 inches in diameter. The bulb will not function in smaller or larger bases; forcing the bulb in place can cause damage to the bulb and light or cause injury or fire. Bulbs can also become hot to the touch very quickly, so it is important to allow the bulb to cool down before touching or replacing a light bulb.