Back in the early 19th century, the invention of the dynamo brought promises of an exciting new world ahead, but the most urgent need of the day, or rather the night, was lighting. Edison's revolutionary incandescent light bulbs had not been invented yet, but Sir Humphry Davy, who can be considered the true founder of electric lighting, had demonstrated at the very beginning of the century a method to produce light by bringing two metal electrodes very close together to produce a sustained spark. Known as arc lamps, these became the first practical electric lights.
A carbon arc lamp consist of two carbon rod electrodes in free air, and connected to a source of electric current. The electric arc is struck by touching the rods together and then slowly drawing them apart to create an arc across the gap. The heat vaporizes the tips of the carbon rods and the highly luminous carbon vapor produces an intense bright light.
New Orleans Riverfront electrically luminated at night, 1883. Sketch by J. O. Davidson
Although the invention of the arc lamp was a spectacular feat, it became obvious that their use would be limited. The light produced by the arc lamp was too intense to be endured at close range, making them unsuitable for indoor use. Even when installed outdoors at the height of typical street lights, these lamps required shielding to reduce the glare which meant that much of their light was wasted. The city of San Jose, California, tried to solve the problem in 1881 by putting arc lights atop a 237-foot tall tower. A total of 6 arc lights were installed boasting a total light output of 24,000 candlepower.
Inspired by San Jose, many American and European cities began putting up lighting towers. These came to be known as Moonlight Towers because the way it mimicked the shining moon. A single tower illuminated several blocks at once, and there was enough light to read one’s pocket watch a quarter of a mile away.
One of the main disadvantages of Moonlight Towers was they needed to be serviced throughout the night. Early arc lamps lasted just an hour or two because the carbon rods would be exhaust by then requiring them to be frequently replaced (later models could last through the night). The heights of the towers posed additional climbing challenge. Because of the cost and labor intensive operation, arc lamps didn’t completely phase out existing oil lamp and gas flame street lights. In most American cities, the lighting towers only complemented gas and oil lamps. Detroit was the only large city in the US lighted wholly and exclusively by the tower system.
A moonlight tower in front of City Hall, Detroit, Michigan, about 1900. Photo credit: Lycurgus S. Glover
Detroit erected a total of 122 towers, with a height of 100 to 180 feet, lighting 21 square miles of the city. It was the best-lighted city in the world. The lighting infrastructure in Detroit was regarded as the future of street lighting, and stood as an example for the rest of the US. By 1884 there were already more than 90,000 arc lamps lighting American cities, and that number rose to 235,000 in 1890. The numbers doubled in another ten years and tripled in five more years.
Arc lamps were in use until around 1920s. By then Edison had substantially improved incandescent lamps that used filaments. These lamps had longer lives and could be produced in smaller powers allowing them to be used inside buildings and small rooms. Eventually, incandescent lamps and later halogen lamps replaced arc lamps.
Most lighting towers were demolished during the first two decades of the 20th century. Some collapsed during storms and tornados. The only ones that remain today are in Austin, Texas, and they are still working, albeit not by means of arc lights. The city originally purchased 31 moonlight towers from Detroit. 17 still survive.
While lighting towers became extinct, arc lights found use in new applications such as cinema projection, spotlights and searchlights. Even in these applications conventional carbon arc lamps are being pushed into obsolescence by xenon arc lamps, but were still being manufactured as spotlights at least as late as 1982.
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