An old-style light bulb turns about 95 percent of its power into heat
A classic incandescent bulb heats a tungsten coil until it glows, and only 2 to 5 percent of the electricity comes out as visible light. Getting even that far took more than a century of experiments and patent fights, and the bulb has now largely given way to the LED.
Before electric light spread in the early 20th century, people relied on candles, gas, oil lamps and fire. Alessandro Volta's battery of 1799 to 1800 could heat copper wire until it glowed, Vasily Petrov produced a lasting electric arc in 1802, and Humphry Davy demonstrated an arc lamp a few years later. Arc lamps, glowing between two carbon rods, became the first practical electric lights and from the 1870s lit streets and big buildings.
Filament bulbs had a longer road. In 1840 Warren de la Rue sealed a platinum coil in a vacuum tube, betting on the metal's high melting point. In the late 1870s Joseph Swan in Britain and Thomas Edison in the United States independently built working lamps; Swan's filaments were too thick, while Edison pursued thinner ones and better vacuums. Rather than keep fighting, the rivals merged into the Edison and Swan Electric Light Company, and by the early 1900s their bulbs had ousted arc lamps. William Coolidge's tungsten filament, patented in 1912, became the long-running standard.
Other technologies followed. Georges Claude showed the first neon light in 1910, launching the neon sign. Fluorescent tubes fill glass with low-pressure mercury vapour or argon; current makes the gas emit ultraviolet, and a phosphor coating inside turns that into visible light. The first practical LED appeared in 1962 but glowed only deep red and served in indicator lights and number displays.
The breakthrough came in 1994, when Shuji Nakamura of Nichia Corporation demonstrated a bright blue LED. Coating blue LEDs with a phosphor that converts part of their light yielded white, and lighting was transformed. Through the early decades of this century regulations and buyers' taste for efficient, long-lasting lamps drove a worldwide phase-out of incandescent bulbs.
Source: Electric light
