The concept of carbon-arc lighting was first demonstrated by
Humphry Davy in the early 19th century, but sources disagree about the year he first demonstrated it; 1802, 1805, 1807 and 1809 are all mentioned. Davy used charcoal sticks and a two-thousand-
cell battery to create an arc across a gap. He mounted his electrodes horizontally and noted that, because of the strong convection flow of air, the arc formed the shape of an arch. He coined the term "arch lamp", which was contracted to "arc lamp" when the devices came into common usage. In the late nineteenth century, electric arc lighting was in wide use for public lighting. The tendency of electric arcs to flicker and hiss was a major problem. In 1895,
Hertha Ayrton wrote a series of articles for
The Electrician, explaining that these phenomena were the result of oxygen coming into contact with the carbon rods used to create the arc. In 1899, she was the first woman ever to read her own paper before the
Institution of Electrical Engineers (IEE). Her paper was "The Hissing of the Electric Arc". The arc lamp provided one of the first commercial uses for electricity, a phenomenon previously confined to experiment, the telegraph, and entertainment.
Carbon-arc lighting in the U.S. In the United States, there were attempts to produce arc lamps commercially after 1850, but the lack of a constant electricity supply thwarted efforts. Thus electrical engineers began focusing on the problem of improving
Faraday's dynamo. The concept was improved upon by a number of people including and
Charles F. Brush. It was not until the 1870s that lamps such as the
Yablochkov candle were more commonly seen. In 1877, the
Franklin Institute conducted a comparative test of dynamo systems. The one developed by Brush performed best, and Brush immediately applied his improved dynamo to arc-lighting, an early application being
Public Square in
Cleveland, Ohio, on April 29, 1879. Despite this,
Wabash, Indiana claims to be the first city ever to be lit with "Brush Lights". Four of these lights became active there on March 31, 1880. Wabash was a small enough city to be lit entirely by 4 lights, whereas the installation at Cleveland's Public Square only lit a portion of that larger city. In 1880, Brush established the
Brush Electric Company. The harsh and brilliant light was found most suitable for public areas, such as Cleveland's Public Square, being around 200 times more powerful than contemporary
filament lamps. The usage of Brush electric arc lights spread quickly.
Scientific American reported in 1881 that the system was being used in: 800 lights in rolling mills, steel works, shops, 1,240 lights in woolen, cotton, linen, silk, and other factories, 425 lights in large stores, hotels, churches, 250 lights in parks, docks, and summer resorts, 275 lights in railroad depots and shops, 130 lights in mines, smelting works, 380 lights in factories and establishments of various kinds, 1,500 lights in lighting stations, for city lighting, 1,200 lights in England and other foreign countries. A total of over 6,000 lights were actually sold. There were three major advances in the 1880s:
František Křižík invented in 1880 a mechanism to allow the automatic adjustment of the electrodes. The arcs were enclosed in a small tube to slow the carbon consumption (increasing the life span to around 100 hours).
Flame arc lamps were introduced where the carbon rods had metal salts (usually magnesium, strontium, barium, or calcium fluorides) added to increase light output and produce different colours. In the U.S., patent protection of arc-lighting systems and improved dynamos proved difficult and as a result the arc-lighting industry became highly competitive. Brush's principal competition was from the team of
Elihu Thomson and
Edwin J. Houston. These two had formed the American Electric Corporation in 1880, but it was soon bought up by
Charles A. Coffin, moved to
Lynn, Massachusetts, and renamed the
Thomson-Houston Electric Company. Thomson remained, though, the principal inventive genius behind the company patenting improvements to the lighting system. Under the leadership of Thomson-Houston's patent attorney,
Frederick P. Fish, the company protected its new patent rights. Coffin's management also led the company towards an aggressive policy of buy-outs and mergers with competitors. Both strategies reduced competition in the electrical lighting manufacturing industry. By 1890, the Thomson-Houston company was the dominant electrical manufacturing company in the U.S. Around the turn of the century arc-lighting systems were in decline, but Thomson-Houston controlled key patents to urban lighting systems. This control slowed the expansion of incandescent lighting systems being developed by
Thomas Edison's
Edison General Electric Company. Conversely, Edison's control of direct current distribution and generating machinery patents blocked further expansion of Thomson-Houston. The roadblock to expansion was removed when the two companies merged in 1892 to form the
General Electric Company. In 1915,
Elmer Ambrose Sperry began manufacturing his invention of a high-intensity carbon arc
searchlight. These were used aboard warships of all navies during the 20th century for signaling and illuminating enemies. In the 1920s, carbon arc lamps were sold as family health products, a substitute for natural sunlight. Arc lamps were superseded by filament lamps in most roles, remaining in only certain niche applications such as
cinema projection,
spotlights, and searchlights. In the 1950s and 1960s the high-power D.C. for the carbon-arc lamp of an outdoor drive-in projector would typically be supplied by a
motor–generator combo (AC motor powering a DC generator). Even in these applications conventional carbon-arc lamps were mostly pushed into obsolescence by
xenon arc lamps, but were still being manufactured as spotlights at least as late as 1982 and are still manufactured for at least one purpose – simulating sunlight in "accelerated aging" machines intended to estimate how fast a material is likely to be degraded by environmental exposure. Carbon arc lighting left its imprint on other film projection practices. The practice of shipping and projecting motion pictures on 2,000-foot reels, and employing "changeovers" between two projectors, was due to the carbon rods used in projector lamphouses having a lifespan of roughly 22 minutes (which corresponds to the amount of film in said reels when projected at 24 frames/second). The projectionist would watch the rod burn down by eye (though a peephole like a welder's glass) and replace the carbon rod when changing film reels. The two-projector changeover setup largely disappeared in the 1970s with the advent of xenon projector lamps, being replaced with
single-projector platter systems, though films would continue to be shipped to cinemas on 2,000-foot reels. == See also ==