Decorative lighting for the one hundredth anniversary celebration of the U.S. Patent Office was provided by fluorescent lamps, setting the stage for the widespread use of this efficient form of lighting.
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. A transport liner over the city was about to radio the names of the twelve greatest American inventors, as chosen by the Patent Office, and as the distinguished group strained to listen for those names, “the room was flooded for a moment by the most brilliant light yet used to illuminate a space that size.” This is how The New York Times summarized the commercial introduction of the fluorescent lamp on the day following the event. Among the twelve inventors named as greatest were Thomas Alva Edison, Robert Fulton, Charles Goodyear, Cyrus Hall McCormick, and Samuel F. B. Morse, but the list did not include the name of the inventor of fluorescent lighting. The honor for inventing fluorescent lighting is shared by many who participated in a series of discoveries over a very long period.
The fluorescent lamp operates as a low-pressure, electric discharge inside a phosphor-coated glass tube that contains a droplet of mercury and a rare gas, commonly argon. At room temperature, the droplet gives off a very weak vapor of mercury atoms. Because mercury ionizes more easily than the rare gas atoms, the mercury atoms control the discharge despite the much larger number of rare gas atoms. The inside of the glass tube is coated with fine particles of the phosphor, a material that fluoresces when bathed in the strong ultraviolet radiation from the mercury atoms in the discharge. The light from a fluorescent lamp is composed mainly of the broad-spectrum, whitish light from the phosphor with a small, but significant, contribution from narrow-spectrum mercury emissions in the violet, blue, green, and yellow. In contrast to an incandescent lamps, a fluorescent lamp gives off light with little heat.
The high light efficiency of the fluorescent lamp is caused by a finely tailored match between the phosphor coating within the lamp and the mercury discharge. Commercial production of the fluorescent lamp followed only after a long sequence of events that instructed scientists on the colorful properties of fluorescent materials and of electrical discharges.
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 continued its glow after exposure to strong sunlight. After exposure to the sun, the material gave off a bluish glow in the dark. 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.
Sir Isaac Newton, who favored the particle theory of light, studied fluorescence and incorrectly attributed the delayed emission of light to the time spent undergoing internal reflections within the grains of the substance. Sir George Gabriel Stokes, who favored the wave theory of light, studied the phenomenon as well. In 1852, he termed the afterglow “fluorescence” and announced a law that summarized the findings on fluorescent substances: The exciting light always has a shorter wavelength than the fluorescing light. For example, short wave violet light can produce longer wave green fluorescence, but green light does not produce violet fluorescence.
It is now known that shorter wavelengths correspond to higher light frequencies and energies, with frequency energies increasing from red, yellow, and green through to violet and ultraviolet. Shorter wavelengths of light thus correspond to higher packets of energy. Stokes’s law requires that the exciting light must be more energetic than the emitted fluorescence. Although light does have particle-like properties, the delayed emission is not caused by internal reflections; rather, it is caused by a real delay in emission during which the energy is held within individual atoms, or groups of atoms, inside the fluorescent material.
While these advances were being made on fluorescent substances, other workers were taking the steps needed to bring about practical discharge that could produce energetic light. In 1706, Francis Hauksbee fabricated an electrostatic generator. He then used a vacuum pump produced by Otto von Guericke to evacuate a vessel to a low pressure and tested his electrostatic generator. Therefore, Hauksbee obtained the first human-made electrical glow discharge by capturing lightning in a jar. Later, investigators worked on this novel form of trapped lightning. 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.”
A variety of scientists and inventors studied Geissler tubes extensively. 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 lamp.
By the 1920’s, a number of investigators 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 back to visible, the Hewitt lamp made an excellent light source.
Scientists learned that the mercury vapor was proper if the coolest portion on the discharge wall was kept between 40 and 45 degrees Celsius, quite cool for a lamp. Under these conditions, the scientist found that 60 percent of the electrical energy entering the discharge appeared as ultraviolet energy radiating from the mercury atoms in the discharge.
Several commercial European laboratories began development of a practical fluorescent lamp in the early 1930’s. Around 1934, laboratories in the United States undertook earnest efforts toward production. A range of durable and efficient phosphors were devised. Sturdy, but inexpensive, electrodes were designed for operation with special metal-oxide coatings that, when heated in the lamp, readily boiled off electrons to supply current to the discharge and so reduced the operating voltage from the high value found in the Hewitt lamp. At the same time, engineers developed the transformer circuitry needed to start the lamp at somewhat elevated voltage and then operate it at the lower voltage available on the electrical lines. Finally, the light coming from the developing fluorescent lamps had to be measured and compared with other light sources. Electrical power is measured in watts; light power is measured in lumens. Invisible powers, such as ultraviolet and infrared light, contain no lumens. The number of lumens per watt of actual power thus must depend on color within the spectrum of visible light. Per watt, violet and red give fewer lumens than green and yellow, which lie near the middle of the spectrum, where the eye is most sensitive. The measurements demonstrated that the fluorescent lamp was quite efficient, at least twice that of an incandescent lamp of similar light output, depending on the phosphor blend chosen for the fluorescent lamp.
Early in 1936, the U.S. Patent Office announced plans for its centennial celebration, and new discoveries were invited for presentation. Fluorescent lighting was chosen to be among the new inventions displayed. On November 23, 1936, fluorescent lighting debuted, and an extraordinary editorial in The New York Times on November 24 carried these words: “We must look for the revolutionary inventions to come—engines driven by atomic energy, rocket ships that voyage in interplanetary space, lamps that glow without heat.”
The revolution of light that glowed without heat took place almost immediately. By 1938, production of fluorescent lamps was well under way. By April, 1938, four sizes of fluorescent lamps in various colors were offered to the public and more than 200,000 lamps were sold. When the United States entered World War II, the demand for efficient factory lighting soared. In 1941, more than 21 million fluorescent lamps were sold.
During 1939 and 1940, two great expositions—the New York World’s Fair
Technical advances improved the fluorescent lamp, especially in the area of light efficiency, commonly rated in lumens per watt. Depending on its exact shade, a perfectly efficient white source may yield 200-300 lumens per watt, whereas a common twenty-first century 100-watt incandescent lamp with a normal lifetime of 750 hours of use has a light efficiency of slightly more than 17 lumens per watt. Even in 1938, the common 40-watt fluorescent lamp had an efficiency of about 45 lumens per watt. This efficiency increased to more than 57 lumens per watt by 1948 and to nearly 80 lumens per watt by the mid-1980’s. All of this was accompanied by large increases in the useful life of the fluorescent lamp from about 2,000 hours in 1942 to nearly 20,000 hours by the mid-1980’s.
The fluorescent lamp did have a number of drawbacks that limited complete acceptance, and some of these persisted. One limitation is the need for a transformer ballast to operate the lamp; this has prevented the widespread use of fluorescent lamps in homes in the United States. It is much simpler to insert an incandescent lamp into a light socket than to replace a fluorescent lamp in a bulky light fixture. Another disadvantage of fluorescent lamps is their relatively poor color rendition in comparison with sunlight and incandescent lamps. In comparison with the color of high-pressure mercury-vapor lamps and sodium-vapor lamps, used for lighting highways and large areas, the color rendition of fluorescent lamps is excellent. The color of fluorescent lamps, however, is not highly uniform across the spectrum, because of the strong blue and green lines of mercury. Also, it is deficient in the red in comparison with sunlight and, especially, in comparison with the incandescent lamp. Because red colors are especially flattering to the skin tones of most people, the use of fluorescent lighting has been severely limited in the home and in mood settings outside the home.
Despite the limitations of the fluorescent lamp, this new form of lighting offered the enormous advantages of high efficiency, long life, and relatively low cost. When it was introduced in 1936, a new industry was born. Within three years after production of the first commercial fluorescent lamps, the industry had reached $100 million in sales. In comparison, the automobile industry took fifteen years after the first cars were produced to reach that sales figure, and the radio industry needed five years.
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Bova, Ben. The Beauty of Light. New York: John Wiley & Sons, 1988. Provides an excellent, readable account of light: how it is seen, how it is used, and how it affects people. Chapter 14 discusses light sources, including fluorescent lighting and its deficiencies. -
Bowers, Brian. Lengthening the Day: A History of Lighting Technology. New York: Oxford University Press, 1998. Concise history of lighting technologies, including fluorescent lighting. Discusses both technical aspects of different lighting technologies as well as the societal effects of advances in such technologies. Well illustrated, with exploded diagrams and reproductions of etchings. -
Elenbaas, W., ed. Fluorescent Lamps. New York: Macmillan, 1959. Collection of articles by experts provides technical details about the fluorescent lamp. -
Kane, Raymond, and Heinz Sell, eds. Revolution in Lamps: A Chronicle of Fifty Years of Progress. 2d ed. New York: Fairmont Press, 2001. A history of the progress made in lamps and lighting as well as information on new lighting technologies, aimed at designers, engineers, and architects as well as lay readers. Includes a chapter on fluorescent lamps. -
Stern, Rudi. The New Let There Be Neon. New York: Harry N. Abrams, 1988. An atlas of vivid neon lights. Includes a survey of the historical development of gas-discharge and related types of lamps. -
Zwikker, C., ed. Fluorescent Lighting. New York: Elsevier Press, 1952. Provides a good mix of technical detail and information on the historical development and practical aspects of fluorescent lamps.
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