Arc lamp
[1] It continued in use in more specialized applications where a high intensity point light source was needed, such as searchlights and movie projectors until after World War II.
The carbon arc lamp is now obsolete for most of these purposes, but it is still used as a source of high intensity ultraviolet light.
Lightning is a similar principle where the atmosphere is ionized by the high potential difference (voltage) between earth and storm clouds.
The outer glass envelope can reach 500 degrees Celsius, therefore before servicing one must ensure the bulb has cooled sufficiently to handle.
The Vortek water-wall plasma arc lamp, invented in 1975 by David Camm and Roy Nodwell at the University of British Columbia, Vancouver, Canada, made the Guinness Book of World Records in 1986 and 1993 as the most powerful continuously burning light source at over 300 kW or 1.2 million candle power.
Although invisible wavelengths were unknown at the time of their invention, unenclosed lamps were soon discovered to produce large amounts of infrared and harmful ultraviolet-radiation not found in sunlight.
However, the arc contributes very little of the light output, and is considered non-luminous, as most of its emission occurs in spectral lines in the violet and UV portions of the spectrum.
He mounted his electrodes horizontally and noted that, because of the strong convection flow of air, the arc formed the shape of an arch.
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.
[10] The arc lamp provided one of the first commercial uses for electricity, a phenomenon previously confined to experiment, the telegraph, and entertainment.
[11] In the United States, there were attempts to produce arc lamps commercially after 1850, but the lack of a constant electricity supply thwarted efforts.
The concept was improved upon by a number of people including William Edwards Staite [de] and Charles F. Brush.
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.
Conversely, Edison's control of direct current distribution and generating machinery patents blocked further expansion of Thomson-Houston.
The problem was solved by adding a sheet of ordinary window glass in front of the lamp, blocking the ultra-violet.
[18] In the 1920s, carbon arc lamps were sold as family health products, a substitute for natural sunlight.
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[20] 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.
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.
