NO. 2 HISTORY OF ELECTRIC LIGHT SCHROEDER 9I 



considerations, which also apply to vacuum lamps, that affect the 

 efificiency. Some of these are: the number of anchors used, as they 

 conduct heat away ; in very low voltage lamps having short filaments 

 the relative amount of heat conducted away by the leading-in wires 

 becomes of increasing importance, etc. The looo-watt lamp for iio- 

 volt circuits is now made for nearly 20^ lumens per watt ; the 50-watt 

 lamp a little over 10 1-p-w. 



The advent of the tungsten filament and especially the gas-filled 

 lamp sounded the doom of all other electric illuminants except the 

 magnetite and mercury arc lamps. All other incandescent lamps have 

 now practically disappeared. The flame arc as well as the enclosed 

 carbon arc lamp are hardly ever seen. The simplicity of the incan- 

 descent lamp, its cleanliness, low first cost, low maintenance cost and 

 high efficiency of the tungsten filament have been the main reasons 

 for its popularity. 



TYPES AND SIZES OF TUNGSTEN LAMPS NOW MADE 



There are about two hundred different types and sizes of tungsten 

 filament lamps now standard for various kinds of lighting service. 

 For iio-volt service, lamps are made in sizes from 10 to 1000 watts. 

 Of the smaller sizes, some are made in round and tubular-shaped bulbs 

 for ornamental lighting. In addition there are the candelabra lamps 

 used in ornamental fixtures. Twenty-five- to five hundred-watt lamps 

 are made with bulbs of special blue glass to cut out the excess of red 

 and yellow rays and thus produce a light approximating daylight. 



For 220-volt service lamps are made in sizes of from 25 to 1000 

 watts. For sign lighting service, 5-watt lamps of low voltage are 

 made for use on a transformer located near the sign to reduce the 

 no volts alternating current to that required by the lamps. Lamps 

 are made from 5 to 100 watts for 30-volt service, such as is found in 

 train lighting and in gas engine driven dynamo sets used in rural 

 homes beyond the reach of central station systems. Concentrated 

 filament lamps are made for stereopticon and motion picture projec- 

 tion, floodlighting, etc., in sizes from 100 to 1000 watts, for street 

 railway headlights in sizes below 100 watts and for locomotive head- 

 lights in sizes from 100 to 250 watts. For series circuits, used in 

 street lighting, lamps are made from 60 to 2500 candlepower. ^linia- 

 ture lamps cover those for flashlight, automobile, Christmas-tree, 

 surgical and dental services, etc. They range, depending on the 

 service, from ^ to 21 candlepower, and in voltage from 2^ to 24. 



