Fluorescent lights have been the primary source of industrial lighting indoors since the 1930s, but recent advances have put compact fluorescent lights in the spotlight for home use.

Fluorescence of rocks and other chemicals had been observed for hundreds of years before it was understood. In 1852 George Stokes named the phenomenon "fluorescence" after the mineral fluorite, a naturally occurring calcium fluoride that glows under ultraviolet light.

By the middle of the 19th century, various scientists had observed a radiant glow from glass tubes from which air had been evacuated when an electric current passed through them.

Thomas Edison received a patent for a fluorescent lamp in 1907 that used a coating of calcium tungstate excited by X-rays. It had a short operating life, and the success of the incandescent lamp made it unfeasible to pursue any alternative electric lighting.

Edison’s rival Nikola Tesla devised high-frequency-powered fluorescent bulbs that emitted a greenish light, but like Edison he had no commercial success with it.

By the 1930s all of the major discoveries and advancements of fluorescent lighting were in place. After years of patent disputes, General Electric introduced the first commercially viable fluorescent tubes in 1938.

By 1951 more fluorescent lamps produced more light than incandescent lamps in the United States, but the greenish glow and barely perceptible flicker were less than satisfactory.

Modern fluorescent lamps contain mercury vapor and a noble gas (neon, argon, xenon, krypton) at low pressure, around 0.3 percent of atmospheric pressure. The inner surface coating is a mixture of varying blends of metallic and rare earth salts.

In principle the fluorescent light is simple: Electrically excited mercury atoms emit ultraviolet light that falls upon the phosphors, causing them to glow.

In practice, getting the mercury to the state where it will emit and maintain the UV light is an obstacle.

First the mercury in the tube must be heated to form a vapor. When the power is connected, an internal cathode becomes hot enough to emit electrons. These electrons collide with and ionize noble-gas atoms to form plasma, which allows higher current to flow through the tube, which increases the collisions with mercury atoms. Once the mercury atoms are ionized, the resistance of the lamp decreases, and it would quickly self-destruct if the voltage remained constant due to unrestricted current flow. To prevent this, lamps use a ballast to regulate the current flow.

In older lamps the ballast used an inductance coil and a capacitor in series. Modern CFLs contain electronic components that use transistors to control start-up heating, change the 60 Hz household current into high-frequency AC and act as ballasts to control the current flow in the lamp.

CFLs represent the confluence of much science and many technologies that now can reproduce virtually any spectral color and use 20 percent to 30 percent of the electricity of a comparable incandescent, while lasting eight to 15 times longer. Even with a higher purchase price, a typical CFL will save more than five times its purchase price in electricity over its lifetime.

Richard Brill is a professor of science at Honolulu Community College. Email questions and comments to brill@hawaii.edu.