Electricity and the Electric Light
Electricity and the Electric Light
Illuminating Possibilities. The possibility of creating artificial light with electricity was established as early as 1808, when the English chemist Sir Humphry Davy demonstrated that current from batteries can create light either by heating some substance until it glows or by causing an arc of electricity to jump over a gap between two conductors. Arc lighting uses a lot of current and i creates a brilliant light and it was limited to the outdoors or large interior spaces. The problem of lighting smaller spaces—which technicians of the nineteenth century called subdividing the light—was to find a lighting material that would not burn or melt when the current ran through it. Carbon and platinum seemed most promising but not ideal: the first does not melt, but it burns easily, while the second resists chemical changes at high temperatures (oxidation) but catches fire if the temperature becomes too high. All of the early lighting experiments were with low-resistance lamps, that is, lamps in which very little of the electrical energy passing through them is dissipated as heat. These lamps used a great deal of low-voltage current.
Edison’s Experiments. When Thomas Alva Edison (1847-1931) began his experiments at his laboratory in Menlo Park, New Jersey, in 1878, he realized that he could prevent the platinum filament from burning if he could put it in a glass bulb with all the air removed from it. At the same time he was trying to conceptualize an extensive system of lighting powered by generators. It occurred to him that a system of several hundred low-resistance lamps would require huge generators and large conducting wires in order to accommodate the current i required. But, he reasoned, high-resistance, high-voltage lamps would need much less current to produce the same amount of light. (According to Ohm’s law, L which Edison applied but did not completely understand, the electric current flowing through a given resistance is equal to the applied voltage divided by the resistance.) This new system could distribute current efficiently from a central station through reasonably sized lines.
The Invention of the Light Bulb. Having solved the conceptual problem, Edison next had to find a material for a light-bulb filament that would glow for a long time without burning up. Finally, on the night of 22 October 1879, his famous bulb number 9, with a carbon filament,
stayed lit for almost fifteen hours. The following week he patented a bulb with a carbon filament. He then applied this technology by illuminating the town of Menlo Park, causing such a sensation that special trains ran from New York City so that people could view the spectacle at night.
From Bulb to System. Having made his earlier experiments with electricity from batteries, Edison next had to develop a dynamo, or generator, to produce a steady current capable of sustaining a large, integrated electrical system. The Menlo Park system ran on a series of small generators. At the Paris Electrical Exposition in 1881 he exhibited a large steam-run dynamo, causing great excitement. The following year he unveiled a small generator-driven electrical plant at the famous Crystal Park Exhibition in London. In December 1880 the Brush Electric Light Company began operation in New York City, illuminating Broadway with arc lights, thus creating the “Great White Way” of theatrical legend. Although it was not in direct competition with Edison, the beginning of the Brush electric service impelled Edison to push even harder to complete an underground electric-wire system for a generating station with a machine works and a lamp works in the Pearl Street district of lower Manhattan. Almost a year passed before the underground wire system was complete. Meanwhile he established free-standing “isolated” systems, mainly for factories, which allowed him to test most of his components. Finally, on 4 September 1882, the Pearl Street electrical station came on line, beginning a new era of urban life.
Robert Friedel and Paul Israel, Edison’s Electric Light: Biography of an Invention (New Brunswick, N.J. : Rutgers University Press, 1987).