The primary light standard, the electric incandescent lamp, using commercial current or current generated at the station, has re placed the older kerosene oil vapour apparatus. Incandescent elec tricity is most satisfactory because of its power, convenience and adaptability. 'It is efficient to electrify certain stations for illum inant, operating sound fog signal and radio-beacon, and lighting buildings.
Electricity is very convenient for signals controlled remotely, as those near jetty ends. Small plants or primary cells generate electric energy for minor lights. The principal difficulty in putting incandescent electric lamps in old lenses is the too concentrated light source, and insufficient divergence of beam ; this is being overcome by various methods.
Acetylene gas compressed in cylinders is increasingly used for unwatched or semi-watched lights of medium importance. Acety lene under incandescent mantles, or more elaborate acetylene apparatus is not used. Electric and dissolved acetylene equipment has advanced automatic apparatus installation and conversion to unattended stations. About 6o% of lights, including buoys and excluding rivers, are now automatic.
Automatic apparatus extends lighthouse facilities to remote regions like Alaska.
Distinguishing principal coast lights by flashing or occulting characteristics, and eliminating fixed lights, progresses steadily. Characteristics are simple, quickly and easily recognized without timing. Preferred limitations are: that a single important light flash be not less than 0.3 sec. in duration, a minor light not less than o•1 sec., that the characteristic be repeated preferably twice a minute, and one light of a range, or two lights in line, be fixed. Colour is valuable in distinguishing but illumination is reduced to about 30%—a serious drawback. Red and green are used for secondary lights.
formity in buoyage and lights would add safety and convenience to navigation. Limited but important action on this at the Inter national Marine Conference, Washington, 1889, resulted in con siderable uniformity.
The United States system, based largely on the 1889 confer ence, is, for vessels coming from sea : red buoys, conical-shaped ("nun") , even numbers, on right side of channel ; cylindrical black buoys, flat tops ("can"), odd numbers on left side; hori zontal red and black-banded buoys mean shoals or dangers; verti cal black and white stripes show clear channels; with coloured lights, red on right and green on left of entrances or channels, but white may be on either side.
Colour and shape to mark the relations of buoys to channels are in nearly world-wide use ; shape alone is not enough, because not readily applicable to important classes of buoys, such as gas, whistle, bell and spar. Moreover, experience shows that both colour and shape do not differentiate too much the respective channel sides. Colour is the most obvious, readily applied char acteristic, and there is far greater world colour uniformity than in other buoy characteristics. The Washington Conference recom mendations now embrace about 8o% of world buoyage, including France, Germany, Scotland, Ireland, Argentina, United States, Canada, Japan, India, China, Philippines, Australia, New Zealand. The American buoyage system, light characteristics and apparatus are as simple as may be, so as to avoid confusion, and to be more definite and reliable.
Lightships are placed, on foggy coasts, to mark outstanding dangers, or port approaches. The first was placed in Chesapeake bay (1820).
Fixed structures on shoals, or gas buoys, have replaced many originally placed in inland waters; Great Lakes lightships are thus being gradually retired. There are 31 lightships stations, with 10 relief ships. Of the stations 25 are outside on the Atlantic and Pacific coasts, where it is impracticable to build lighthouses, yet where they are vital to traffic, i.e., Nantucket lightship moored in 3o fathoms, 41 m. from land, guards shoals to the north and most trans-ocean vessels approaching the United States Atlantic coast steer for this vessel, one of the world's most important sea marks.