Miniature electric lamps include all that are not used for general illuminating purposes. The term applies more particularly to the form of the base than to the voltage or candlepower of the filament. There are three general classes of these lamps: candelabra and decorative, that operate on lighting circuits of 100 to 130 volts and are usually intended for decorative purposes; general battery lamps used for flash lights; and lamps for automobiles and electric-vehicle service.

Candelabra screw base.

Minature screw base.

Double-contact bayonet candelabra base.

Single-contact bayonet candelabra base.

Fig. 221. - Miniature lamp bases.

The term miniature lamp applies more particularly to the base than to the voltage or candlepower. The style of base is characteristic of the service for which the lamp is designed rather than the size or number of watts consumed. There are two general styles of bases: the screw type of the Edison construction of which there are two sizes; and the bayonet type of which there are two styles of construction.

Bases for miniature lamps are made in form to suit the conditions of their use. The styles at present are shown in Fig. 221. Of these the screw bases at the left are those attached to small flash-lamp bulbs and others of the smaller sizes of lamps. The two at the right of the figure are the bayonet style used under conditions not suited to the screw contact. In the case of automobile lamps and in places where vibration will cause loss of contact the bayonet base is generally in use. The lamp is held in place by the-projecting lugs that engage with openings in the socket and kept in place by the pressure of a spring. The contact with the lamp filament is made by two terminals that make connection directly with the terminals of the lamp filament. The single contact base is kept in place similarly to that of the other but makes a single contact at the end of the socket while the other but makes a single contact at the end of the socket while the circuit is completed through the pressure exerted between the projecting lugs and the socket.