CARBON-DIOXIDE TUBE FOR
ACCURATE COLOR-MATCHING
The open-arc lamp possessed the disadvantage of emitting a very unsteady light and of consuming the carbons so rapidly that daily trimming was often necessary. In 1893 the enclosed arc appeared and although it consumed as much electrical energy as the open-arc and emitted considerably less light, it possessed the great advantage of operating a week without requiring a renewal of carbons. By surrounding the arc by means of a glass globe, little oxygen could come in contact with the carbons and they were not consumed very rapidly. The light was fairly steady and these arcs operated satisfactorily on alternating current. The latter feature simplified the generating and distributing equipment of the central station.
The magnetite or luminous arc-lamp next appeared and met with considerable success. It was more efficient than the preceding lamps but was handicapped by being solely a direct-current device. Those familiar with the generation and distribution of electricity will realize this disadvantage. However, its luminous intensity just below the horizontal was about 700 candles and its general distribution of light was fairly satisfactory. Later the flame-arcs began to appear and they were installed to some extent. The arc-lamp has served well in street-lighting from the year 1877, when the open-arc was introduced, until the present time, when the luminous-arc is the chief survivor of all the arc-lamps.
MODERN STREET LIGHTING
Tunnels of light boring through the darkness provide safe channels for modern traffic
The carbon incandescent filament lamp was used extensively until 1909, when the tungsten filament lamp began to replace it very rapidly. However, it was not until 1914, when the gas-filled tungsten lamp appeared, that this type of light-source could compete with arc-lamps on the basis of efficiency. The helical construction of the filament made it possible to confine the filament of a high-intensity tungsten lamp in a small space and for the first time a high degree of control of the light of street lamps was possible. Prismatic "refractors" were designed, somewhat on the principle of the lighthouse refractor, so that the light would be emitted largely just below the horizontal. This type of distribution builds up the illumination at distant points between successive street lamps, which is very desirable in street-lighting. The incandescent filament lamp possesses many advantages over other systems. It is efficient; capable of subdivision; operates on direct and alternating current; requires little attention; and is capable of most successful use with light-controlling apparatus.
According to the reports of the Department of Commerce the number of electric arc-lamps for street-lighting supplied by public electric-light plants decreased from 348,643 in 1912 to 256,838 in 1917, while the number of electric incandescent filament lamps increased from 681,957 in 1912 to 1,389,382 in 1917.
Street-lighting is not only a reinforcement for the police but it decreases accidents and has come to be looked upon as an advertising medium. In the downtown districts the high-intensity "white-way" lighting is festive. The ornamental street lamps have possibilities in making the streets attractive and in illuminating the buildings. However, it is to be hoped that in the present age the streets of cities and towns will be cleared of the ragged equipment of the telephone and lighting companies. These may be placed in the alleys or underground, leaving the streets beautiful by day and glorified at night by the torches of advanced civilization.