Fluorescent Lamp
You might think that the everyday light bulb is the most common type of lighting today, but actually--if you count all the offices and factories in the United States--the fluorescent lamp outshines the incandescent light bulb as our main source of electric lighting. The introduction of the fluorescent lamp in 1936 was staged with great drama at the U.S. Patent Office's 100th anniversary celebration, where more than 1,000 people were gathered in a hotel ballroom. Just when the names of America's twelve greatest inventors were being announced, the room was flooded with brilliant fluorescent light. The invention of the lamp resulted from the work of many different scientists over a long period of time, beginning in the 1600s with the discovery of a substance that would glow in the dark after exposure to the sun. The visible glow produced by materials exposed to ultraviolet rays was later named fluorescence by Sir George Gabriel Stokes, who studied various fluorescent substances.
In 1855 a German glassblower, Johann Heinrich Wilhelm Geissler, invented a vacuum pump that could extract most of the air from a tube. Once these vacuum tubes became available, scientists were able to pass electricity through different gases at very low pressures inside the tubes. The electric current would cause certain gases to discharge light, producing a glow. This led to the invention of the mercury vapor discharge lamp in 1901 by Peter Hewitt, an American engineer.
Although the early mercury vapor lamps were quite successful, they produced a high proportion of ultraviolet light, which is invisible to the human eye. Scientists already knew that fluorescent chemicals called phosphors would convert ultraviolet rays to visible light. As early as 1859, Antoine-Henri Becquerel had built a primitive fluorescent lamp by coating the inside of a vacuum tube with a phosphor. During the 1920s and 1930s, laboratories began formulating more durable, efficient phosphor coatings. Engineers also improved the mercury vapor lamp by reducing its operating voltage. The first practical fluorescent lamp was developed by a team of American scientists at General Electric's laboratory around 1934. Soon after its dramatic introduction, the fluorescent light was promoted at the 1939 New York World's Fair and at an exposition in San Francisco. Various colors and sizes were offered, and sales were healthy. Then when America joined World War II, factories began working at full capacity to supply troops, and sales of fluorescent lighting multiplied 100-fold.
Since then, many technical advances have been made, leading to longer life and higher efficiency. Fluorescent lamps now supply two-thirds of lighting demand worldwide. By using different phosphor-coating formulas, a greater variety of shades and colors have been created for different uses. For example, the warmest shades of white, which contain the most red light, are desirable for grocery meat counters, where they make the meat look more appetizing. However, fluorescent light is still somewhat glaring, and the incandescent lamp will continue to reign in people's homes until fluorescent models can produce a cozier, more flattering light.
Recent years have seen great interest in the health effects of fluorescent lighting. In the 1950s John Ott, a banker and photographer, noticed while shooting time-lapse photography for Walt Disney that pumpkin seed sprouts would not fully mature under fluorescent lights. After studies of various laboratory animals, he initiated careful studies in the 1970s of first-grade school children in Florida. Ott determined that students who worked under ordinary cool-white fluorescent lighting demonstrated fatigue and attention problems, but that their behavior noticeably improved if they worked under full-spectrum fluorescent lights, which give off more ultraviolet light than the standard cool-white fluorescent lights. It was even found that students in classrooms with full-spectrum fluorescent lights had fewer dental cavities than those working under cool-white fluorescent lights. Some schools and businesses have begun installing full-spectrum fluorescent lighting in their rooms in the belief that it leaves workers less tired and able to pay better attention to their work.
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