page_title: Peter Cooper Hewitt
section_title: Career
hierarchical_section_title: Peter Cooper Hewitt / Career
caption_attribution_description: English: One of the first mercury vapor lamps created by Peter Cooper Hewitt, which he invented and patented in 1903. This was the forerunner of the fluorescent lamp. It consisted of a sealed partially evacuated glass tube with electrodes at either end, with a small amount of liquid mercury inside. When a pulse of high voltage was applied an arc was started between the electrodes which evaporated the mercury. The electrons struck the mercury atoms, knocking off electrons, ionizing them, so the gas in the tube became electrically conductive, and a current flowed through the tube. When the electrons rejoined the atoms the atoms emitted light. The circular device below the lamp is the ballast, an inductor which produced a pulse of high voltage when the lamp was turned on, to start it. The mercury-vapor lamp was a lot more efficient than the incandescent lamp which was the dominant type of electric light at the time, but it produced a greenish light which was unpleasant, so its use was limited to office buildings and hallways and photographic uses. Later a fluorescent coating (a phosphor) was applied to the inside of the tube, which produced a pleasing white light when struck by ultraviolet light from the mercury vapor. This was the fluorescent lamp which has become most widely used light source today.
context_page_description: Peter Cooper Hewitt was an American electrical engineer and inventor, who invented the first mercury-vapor lamp in 1901. Hewitt was issued U.S. Patent 682,692 on September 17, 1901. In 1903, Hewitt created an improved version that possessed higher color qualities which eventually found widespread industrial use.
context_section_description: In 1901 he invented and patented a mercury-vapor lamp; a gas-discharge lamp that used mercury vapor produced by passing current through liquid mercury.   His first lamps had to be started by tilting the tube to make contact between the two electrodes and the liquid mercury; later he developed the inductive electrical ballast to start the tube.  The efficiency was much higher than that of incandescent lamps, but the emitted light was of a bluish-green unpleasant color, which limited its practical use to specific professional areas, like photography, where the color was not an issue at a time where films were black and white. For space lighting use, the lamp was frequently augmented by a standard incandescent lamp.  The two together provided a more acceptable color.  Later. in the 1930s. a fluorescent coating (phosphor) was added to the inside of the tube at General Electric, which produced more pleasing white light when it absorbed the ultraviolet light from the mercury.  This was the fluorescent lamp, which is now one of the most widely used lamps in the world.
  In 1902 Hewitt developed the mercury arc rectifier, the first rectifier that could convert alternating current power to direct current without mechanical means.  It was widely used in electric railways, industry, electroplating, and high-voltage direct current (HVDC) power transmission.  Although it was largely replaced by power semiconductor devices in the 1970s and 1980s, it is still used in some high power applications.
  In 1903, the degree of Honorary Doctorate of Science was conferred upon him by the Columbia University in recognition of his work.
  In 1907 he developed and tested an early hydrofoil.  In 1916, Hewitt joined Elmer Sperry to develop the Hewitt-Sperry Automatic Airplane, one of the first successful precursors of the cruise missile.
caption: Cooper Hewitt's mercury vapor lamp, the forerunner of the fluorescent lamp.
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