"It is often desirable in interior illumination to run lamps considerably below their normal candle power, as for instance in the case of hall lights burning all night, or in sick rooms and bedchambers. To accomplish this without loss of energy due to the introduction of external resistances, on direct circuits, the Edison general Electric Co. have brought out what is known as their 'night lamp,' which is illustrated in the accompanying engraving, Fig. 1.

"The lamp, as will be seen, is provided with two filaments connected up in the manner shown, and provided with a special switch at the top of the base, which is shown enlarged in Fig. 2. This small auxiiliary switch consists of a short brass tube soldered to the screw ring of the lamp and encircling the screw S, the space between the tube and the screw being filled with insulating material I, and the screw S, being kept from turning by means of the insulating pin P. The screw S is hollow and through it passes the wire W, which is connected to the filaments, which are joined at the centre of the stem.

"Mounted upon screw S, is a brass nut A, which, when screwed up, makes connection between the screw S, and the short brass tube soldered to the screw ring of the base R, to that joined to the ends of the filaments at the centre of the leading-in tube, thus short-circuiting one carbon, and allowing the other to give its full brilliancy. When the nut A is screwed back and in the position shown, both the carbons in the lamp are in series and burn at only a fraction of the normal candle power of the lamp. These night lamps as a rule are frosted and shed a mellow light about the apartment."

Caution - Because of the unknown nature of wiring of some sockets it is suggested to any collector who might have such a lamp to test it with a resistance meter rather than plugging it into 120 volts.

Reference
"The Edison Night Lamp," The Electrical Engineer, Vol 14, Jul 20, 1892, pg 67.