What are the most common socket types?

The most common sockets have been present and used ever since the invention of the light bulb by Thomas Alva Edison as they are easy to produce and can hold the light bulbs in a stable way. These sockets are designed for light sources with various Edison screws that are designated with the letter “E” and a number that specifies the width of the screw base, as in E14, E27.
In an average European household the most widespread light bulbs are those with an E27 and E14 screw base but E10 and E40 sockets are also widely found in various areas of use. E10 screw bases are preferred in torches and Christmas tree lights, while E40 is used in public lighting and various industrial solutions for lighting large halls, as light sources with this screw base may have an output of up to 2000 W.

The second most common socket type is the bayonet base where the light bulb does not have to be fitted into the socket with the help of a screw base, we only need to place the pins on the light bulb into the socket and then turn it firmly. In this case the bulb is held in position by a spring, thus the contact is not disturbed even in the case of vibration. The most widely used bayonet base in households is the GU10, whereby “10” indicates the distance between the two pins in millimeters. These socket types are also widely used in vehicles.

Light sources with a G9 base are used mostly for wall and ceiling lamps. These can be recognized easily from the “U”-shaped, looped-pin base. Number 9 in its name indicates the distance in millimeters between the pins in this case as well.

The socket types listed so far have all been designed for 230V use but there are also those suitable for low current lighting. The GU5.3 and G4 light sources are designed to function at 12V and are used mostly in spotlights and desk lamps. The numbers after “GU” and ”G” also indicate the distance between the pins in millimeter.

In the case of fluorescent tubes, the most widespread is the G13 socket that may be used with a T8 tube. As in the other cases, the number after "T" indicates the distance between the pins in millimeter. 

There are only two types of sockets in the case of linear lights, these are the S14d and S14s. Although the shape and size of the connections is the same in both cases, S14d has only 1 socket in the middle of the linear lamp, while S14s has two sockets at the 2 ends of the lamp.


The last socket type is the R7s, which may be seen mostly in the case of older halogen floodlights and larger floor lamps.