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.

XIII

LIGHTHOUSES

At the present time thousands of lighthouses, light-ships, and light-buoys guide the navigator along the waterways and into harbors and warn him of dangerous shoals.  Many wonderful feats of engineering are involved in their construction and in no field of artificial lighting has more ingenuity been displayed in devising powerful beams of light.  Many of these beacons of safety are automatic in operation and require little attention.  It has been said that nothing indicates the liberality, prosperity, or intelligence of a nation more clearly than the facilities which it affords for the safe approach of the mariner to its shores.  Surely these marine lights are important factors in modern navigation.