Base (lamp)
The base is the part of a lamp that enables its mechanical and electrical connection to the light. It carries or houses the electrical contacts and, in many designs, also ensures that the light source is secured in the correct position.
The base is inserted into the appropriate socket. The base forms part of the light source, whilst the socket is a component of the luminaire or light.
Significance in vehicle headlamps
In the case of replaceable lamps, the base not only determines whether a lamp fits mechanically into a light. Its geometry also ensures that the actual light source is positioned correctly within the optical system.
This is important, for example, with halogen lamps: the position of the filament relative to the reflector or other optical elements influences the beam pattern produced.
Base designations
There are numerous standardised designs for lamp bases, which are identified by combinations of letters and numbers. The letters provide information about the type of base. For example, ‘BA’ denotes a bayonet base for vehicle lamps, ‘P’ a prefocus or adjustable base, and ‘W’ a base integrated into the lamp.
The following numbers refer to a dimension characteristic of the respective base type. Which dimension is meant depends on the base group. For BA bases, for example, the number roughly indicates the diameter of the sleeve; for other designs, it may refer to contact spacing or other relevant dimensions.
This allows different base designs to be clearly distinguished from one another and assigned to the appropriate type of lamp and socket.