Lamp, Incandescent

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LAMP, INCANDESCENT

LAMP, INCANDESCENT. As early as 1820, scientists all over the world had begun to work on the development of an incandescent lamp, but it remained for Thomas A. Edison at Menlo Park, New Jersey, on 21 October 1879 to make the first successful high resistance carbon lamp, which embodied almost all the basic features of lamps commonly in use today.

The first carbon lamp was inefficient in comparison with present-day lamps, giving only 1.7 lumens (light units) per watt (unit of energy). Inventors, many of them American, gradually improved the carbon lamp through minor changes in construction, so that by 1906 it produced 3.4 lumens per watt. In 1905 Willis R. Whitney, head of the research laboratory of the General Electric Company at Schenectady, New York, succeeded in changing the character of the carbon filament to give it metallic characteristics, and for a few years the Gem lamp, which produced 4.25 lumens per watt, was on the market. In 1904 two Austrian chemists, Alexander Just and Franz Hanaman, patented a remarkably efficient tungsten filament lamp, giving 7.75 lumens per watt; however, it was extremely fragile and could be used only under special conditions. At that time it was believed impossible to draw tungsten wire, but in 1910 William D. Coolidge of the General Electric research laboratory succeeded in making ductile tungsten. Lighting manufacturers quickly saw tungsten's advantages of both efficiency and strength, and the drawn-wire tungsten filament lamp shortly superseded all other forms.

All lamps up to this time operated filaments in a vacuum. In 1913, after much experimentation and fundamental research, Irving Langmuir, one of Whitney's assistants, discovered that with the largest sizes of lamps, if the filaments were coiled and the bulbs filled with inert gases, such as nitrogen or argon, the efficiency could be increased to as high as 20 lumens per watt. Gas filling and double coiling of filament have since been introduced into smaller sizes.

The cost of the incandescent lamp has constantly been reduced and efficiency increased. In 1907 the 60-watt lamp gave 8 lumens per watt and lost 25 percent of this light before burning out. Thirty years later the 60-watt lamp produced 13.9 lumens per watt and emitted 90 percent of its original light at the end of its life. By the 1970s developments had brought the number of lumens produced in a tungsten-filament lamp to 40, the maximum obtainable before the filament melts. In the late– twentieth century, concerns about energy use spurred the manufacture of efficient lamp styles, including "long-life bulbs," with thicker tungsten strands, and the more efficient fluorescent and halogen lamps. (Halogen lights use tungsten filiments, but with halogen added to increase the light output.) Although fluorescent and halogen lamps provide more light with greater efficiency, incandescent lamps continued to be used because of their simplicity and low cost.

BIBLIOGRAPHY

Friedel, Robert D., and Paul Israel with Bernard S. Finn Edison's Electric Light: Biography of an Invention. New Brunswick, N.J.: Rutgers University Press, 1985.

Howell, John W., and Henry Schroeder. History of the Incandescent Lamp. Schenectady, N.Y.: Maqua, 1927.

A. L.Powell/a. r.