21 June 2009
lighting The invention: A form of electrical lighting that uses a glass tube coated with phosphor that gives off a cool bluish light and emits ultraviolet radiation. The people behind the invention: Vincenzo Cascariolo (1571-1624), an Italian alchemist and shoemaker Heinrich Geissler (1814-1879), a German glassblower Peter Cooper Hewitt (1861-1921), an American electrical engineer Celebrating the “Twelve Greatest Inventors” On the night of November 23, 1936, more than one thousand industrialists, patent attorneys, and scientists assembled in the main ballroom of the Mayflower Hotel in Washington, D.C., to celebrate the one hundredth anniversary of the U.S. Patent Office.Atransport liner over the city radioed the names chosen by the Patent Office as America’s “Twelve Greatest Inventors,” and, as the distinguished group strained to hear those names, “the room was flooded for a moment by the most brilliant light yet used to illuminate a space that size.” Thus did The New York Times summarize the commercial introduction of the fluorescent lamp. The twelve inventors present were Thomas Alva Edison, Robert Fulton, Charles Goodyear, Charles Hall, Elias Howe, Cyrus Hall McCormick, Ottmar Mergenthaler, Samuel F. B. Morse, George Westinghouse, Wilbur Wright, and Eli Whitney. There was, however, no name to bear the honor for inventing fluorescent lighting. That honor is shared by many who participated in a very long series of discoveries. The fluorescent lamp operates as a low-pressure, electric discharge inside a glass tube that contains a droplet of mercury and a gas, commonly argon. The inside of the glass tube is coated with fine particles of phosphor. When electricity is applied to the gas, the mercury gives off a bluish light and emits ultraviolet radiation.When bathed in the strong ultraviolet radiation emitted by the mercury, the phosphor fluoresces (emits light). The setting for the introduction of the fluorescent lamp began at the beginning of the 1600’s, when Vincenzo Cascariolo, an Italian shoemaker and alchemist, discovered a substance that gave off a bluish glow in the dark after exposure to strong sunlight. The fluorescent substance was apparently barium sulfide and was so unusual for that time and so valuable that its formulation was kept secret for a long time. Gradually, however, scholars became aware of the preparation secrets of the substance and studied it and other luminescent materials. Further studies in fluorescent lighting were made by the German physicist Johann Wilhelm Ritter. He observed the luminescence of phosphors that were exposed to various “exciting” lights. In 1801, he noted that some phosphors shone brightly when illuminated by light that the eye could not see (ultraviolet light). Ritter thus discovered the ultraviolet region of the light spectrum. The use of phosphors to transform ultraviolet light into visible light was an important step in the continuing development of the fluorescent lamp. Further studies in fluorescent lighting were made by the German physicist Johann Wilhelm Ritter. He observed the luminescence of phosphors that were exposed to various “exciting” lights. In 1801, he noted that some phosphors shone brightly when illuminated by light that the eye could not see (ultraviolet light). Ritter thus discovered the ultraviolet region of the light spectrum. The use of phosphors to transform ultraviolet light into visible light was an important step in the continuing development of the fluorescent lamp. The British mathematician and physicist Sir George Gabriel Stokes studied the phenomenon as well. It was he who, in 1852, termed the afterglow “fluorescence.” Geissler Tubes While these advances were being made, other workers were trying to produce a practical form of electric light. In 1706, the English physicist Francis Hauksbee devised an electrostatic generator, which is used to accelerate charged particles to very high levels of electrical energy. He then connected the device to a glass “jar,” used a vacuum pump to evacuate the jar to a low pressure, and tested his generator. In so doing, Hauksbee obtained the first human-made electrical glow discharge by “capturing lightning” in a jar. In 1854, Heinrich Geissler, a glassblower and apparatus maker, opened his shop in Bonn, Germany, to make scientific instruments; in 1855, he produced a vacuum pump that used liquid mercury as an evacuation fluid. That same year, Geissler made the first gaseous conduction lamps while working in collaboration with the German scientist Julius Plücker. Plücker referred to these lamps as “Geissler tubes.” Geissler was able to create red light with neon gas filling a lamp and light of nearly all colors by using certain types of gas within each of the lamps. Thus, both the neon sign business and the science of spectroscopy were born. Geissler tubes were studied extensively by a variety of workers. At the beginning of the twentieth century, the practical American engineer Peter Cooper Hewitt put these studies to use by marketing the first low-pressure mercury vapor lamps. The lamps were quite successful, although they required high voltage for operation, emitted an eerie blue-green, and shone dimly by comparison with their eventual successor, the fluorescent lamp. At about the same time, systematic studies of phosphors had finally begun. By the 1920’s, a number of investigators had discovered that the low-pressure mercury vapor discharge marketed by Hewitt was an extremely efficient method for producing ultraviolet light, if the mercury and rare gas pressures were properly adjusted. With a phosphor to convert the ultraviolet light back to visible light, the Hewitt lamp made an excellent light source. Impact The introduction of fluorescent lighting in 1936 presented the public with a completely new form of lighting that had enormous advantages of high efficiency, long life, and relatively low cost. By 1938, production of fluorescent lamps was well under way. By April, 1938, four sizes of fluorescent lamps in various colors had been offered to the public and more than two hundred thousand lamps had been sold. During 1939 and 1940, two great expositions—the New York World’s Fair and the San Francisco International Exposition— helped popularize fluorescent lighting. Thousands of tubular fluorescent lamps formed a great spiral in the “motor display salon,” the car showroom of the General Motors exhibit at the New York World’s Fair. Fluorescent lamps lit the Polish Restaurant and hung in vertical clusters on the flagpoles along theAvenue of the Flags at the fair, while two-meter-long, upright fluorescent tubes illuminated buildings at the San Francisco International Exposition. When the United States entered World War II (1939-1945), the demand for efficient factory lighting soared. In 1941, more than twenty-one million fluorescent lamps were sold. Technical advances continued to improve the fluorescent lamp. By the 1990’s, this type of lamp supplied most of the world’s artificial lighting.