A great many experiments aimed at the development of a viable incandescent electric
lamp
were conducted during the 1840s. Electric currents were passed thorough strips of carbon and various high resistance metals, heating them till they glowed. No practical advances were evident, however, until 1878, when the first filament lamps with a carbon linear filament were produced by Joseph Swan in England .
Soon after, in 1880, Thomas Edison sealed thin filaments of carbonized threads inside a glass bulb from which all air had been removed by a vacuum, and then passed an electric current through them. The
voltage
was steadily increased until the incandescent filament reached a stable, bright glow. The electric current kept the filament glowing for 40 hours. Although the melting point of carbon is quite high, 3598 °C, the material evaporates at a much lower temperature, and carbon filament lamps had to be operated at a low
temperature
in order to prolong their life. In took another three decades until the
tungsten filament
was developed, in 1907.
Edison was faster to register a patent on his
lamp
than Swan . Edison's invention marked the dawn of electric lighting and the electric age. |
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The swan incandescent carbon filament lamp, as used at the Savoy Theater, 1881.
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