INCANDESCENT LAMPS are very simple com pared with are lamps. The carbon strip or fila ment is bent into the shape of a horseshoe, loop, or some more complex form, and placed inside of a glass bulb called the lamp-chamber. The air is then exhausted from the chamber, most commonly by pumping, after which the chamber is hermetically scaled. The exhaustion of the bulb should be as perfect as possible (see AIR lion. Both the exhaustion and the heating of the lamp must lie continued up to the moment that it is sealed. The ends of the filament are attached to platinum wires passing through one end of the glass bulb, and are called leading-in wires. Filaments are prepared from numerous substances, such as silk, hair, wood-fibre, cotton, Pr:qv), and in order to insure the complete re moval of all the air in the bulb, and the occluded :lases in the carbon filament. both the bulb and the filament are heated to a high temperature during the latter part of the process of exhans cellulose. The most CO111111011 practice now IS to force a plastic solution of cellulose through a hole, thus forming a thread. The filaments re quire baking at high temperatures. in order to reduce them to pure carbon, their other constitu ents being driven 14 by the beat. In some proc esses of making filaments no treatment is re quired after the baking, as the filament is then turned out perfectly even in cross-section through out its length. Alost filaments are not perfectly even in diameter over their whole length, and any unevenness either bright or dull spots when lighted. To comet this, the filament is burned for a few cements in a hydro-ea: thou vapor. The spots which burn brightest on the filament are those of -malle-t diameter, and they have a higher temperature than the rest of the filament. Now carbon is deposited from the hydrocarbon vapor on to the tilment when a certain temperature is reached. and the higher the temperature 1 he faster the deposit. The spots of higher temperature will take on the deposit of carbon faster than the rest of the filament. and in this way the diameter throughout becomes per fect, even in a few moments. Incandescent lamps are generally connected in multiple—that is, each lainp is Connected across the two conductors leading from the poles of the generator. The
energy of power consumed in electric lamps, as in the case of other electrical apparatus. is meas ured in watts, 746 of which are equivalent to a horse-plover. The number of watts in a circuit is obtained by multiplying the strength of cur rent in amperes by the difference in potential in \AN, one watt represents the energy devel oped by a eurrent of one ampere, with a difference of potential of one volt.
III electric lighting the chief consideration is to obtain the maximum amount of light with the least expenditure of energy. An ordinary arc lamp may require 430 watts, or a current of 10 amperes of current at 45 volts, while a le•candle power incandescent lamp might utilize ampere at HO volts, or 53 watts. The actual energy required is increased by losses in the conductors leading to the lamps. Incandescent lamp, now range from 1 candle-power or less, if desired, to, say. 100 candle-power or more, and arc lamps from some 350 candle-power. in the case of the closed lamps. to 2000 candlepower. A far high er power is obtained in lamps designed for spe cial purpose, such a, search-lights (q.v.). In lamps are generally made to operate at voltages of 50 to 60. 100 to 120. and 200 to 230, but special types are constructed with which much lower voltage, are employed. such as bi cycle lamps. taking ampere of current at 5 volt,. and giving candle-power; and surgical lamps u-ing about 1 ampere of current at 3 volts candle-power. Incandescent lamps may be run in series—as in the case of advertis ing signs—on a 110-volt circuit. where each lamp consumes 0.33 amperes at to 15 volts. and gives 1 candle-power: or series incandescent lamps may be placed on a 10-ampere arc circuit, where they utilize about volt per eandle-power. already stated, the ordinary open-arc direct current lamp operates at 45 volts, using from to 10 amperes. The inclosed arcs rim some 30 per cent. higher in voltage. lleterS of various kinds are used to indicate or record the amperage and voltage of electric currents and the energy or power consumed in watts. See E•Ec laic ETER.