Electric light

• 1. Introduction

  ›

  An electric light produces light from electricity, and it is the most common form of artificial lighting in the world. The story behind that simple statement runs more than a century. In 1799 to 1800, Alessandro Volta built the voltaic pile, the first electric battery. Current from those batteries could heat copper wire until it glowed. From that faint incandescence to the bulb in a modern ceiling fixture, the path crossed continents, patents, and rival inventors. How did a heated platinum coil in a vacuum tube become a household object? Why did the glowing filament eventually surrender to glass tubes filled with mercury vapour, and then to a flow of electrons across a semiconductor? And what made the most familiar bulb of the twentieth century begin to vanish in the twenty-first? Light from electricity, it turns out, was never one invention. It was a long argument between heat, gas, and the diode.

• 2. Three Ways To Glow

  ›

  Incandescent lamps make light by heating a filament white-hot with electric current. That is one of three main categories of electric lights, and each works on a different physical idea. Gas-discharge lamps, such as fluorescent lamps, produce light by driving an electric arc through a gas. LED lamps produce light by a flow of electrons across a band gap in a semiconductor. The differences are not cosmetic. A lamp's base, made of ceramic, metal, glass, or plastic, secures it in the socket of a light fixture. The electrical connection to that socket may use a screw-thread base, two metal pins, two metal caps, or a bayonet mount. Modern electric light sources come in a profusion of types and sizes, each adapted to a particular job. Most modern lighting draws on centrally generated electric power. Lighting may also run on mobile or standby generators or battery systems. Battery-powered light is often held in reserve for when and where stationary lights fail, appearing as flashlights, electric lanterns, and the lamps inside vehicles.

• 3. The Century Of Filaments

  ›

  Vasily Vladimirovich Petrov developed the first persistent electric arc in 1802. Four years later, in 1806, the English chemist Humphry Davy gave a practical demonstration of an arc light. Before electric lighting became common in the early twentieth century, people lit their homes with candles, gas lights, oil lamps, and fires. In 1840, Warren de la Rue enclosed a platinum coil in a vacuum tube and passed current through it, building one of the world's first electric light bulbs. His reasoning was sound. Platinum's high melting point let it run at high temperatures, and the evacuated chamber held fewer gas molecules to react with the metal, improving its longevity. The design was efficient, but the cost of platinum made it impractical for commercial use. William Greener, an English inventor, added to early electric lighting with his lamp in 1846, recorded under patent specification 11076. The late 1870s and 1880s brought intense competition. Joseph Swan in the United Kingdom and Thomas Edison in the United States independently developed working incandescent lamps. Swan's bulbs, based on designs by William Staite, succeeded, but their filaments were too thick. Edison pursued thinner filaments and a better vacuum, producing a more commercially viable bulb. Their rivalry ended in a merger, forming the Edison and Swan Electric Light Company, which sold lamps with a new filament designed by Swan. By the early twentieth century these had completely replaced arc lamps. The turn of the century brought longer-lived, more efficient bulbs, especially after William D. Coolidge introduced the tungsten filament and applied for a patent in 1912. It took more than a century of incremental improvement, and a tangle of patents and disputes, to reach commercially produced incandescent bulbs in the 1920s.

• 4. Gas And Glow

  ›

  In 1910, Georges Claude introduced the first neon light, opening the way for the neon signs that filled advertising. Fluorescent light followed a stranger route. In 1934, Arthur Compton, a famous physicist and GE consultant, reported to the GE lamp department on successful fluorescent lighting experiments at General Electric Co., Ltd. in Great Britain, a firm unrelated to General Electric in the United States. Spurred by that report, a team led by George E. Inman built a prototype fluorescent lamp in 1934 at General Electric's Nela Park engineering laboratory in Ohio. The work was anything but trivial. Arthur A. Bright described it this way: "A great deal of experimentation had to be done on lamp sizes and shapes, cathode construction, gas pressures of both argon and mercury vapor, colors of fluorescent powders, methods of attaching them to the inside of the tube, and other details of the lamp and its auxiliaries before the new device was ready for the public." A fluorescent lamp is a glass tube holding mercury vapour or argon at low pressure. Electricity through the tube makes the gases give off ultraviolet energy, and phosphors coating the inside glow when struck by ultraviolet photons. For the same amount of light, fluorescents typically draw about one-quarter to one-third the power of an incandescent. Their luminous efficacy runs 50 to 100 lumens per watt, several times that of comparable incandescent bulbs. The fixtures cost more, because they need a ballast to regulate current, but lower energy bills usually offset that. Because they contain mercury, many fluorescent lamps count as hazardous waste, and some jurisdictions require their recycling.

• 5. The Diode Takes Over

  ›

  The first practical LED arrived in 1962, and it could only display deep red. Those early diodes were inefficient, fit only for numeric displays and indicator lights, useless for general lighting. The breakthrough came in 1994, when Shuji Nakamura of Nichia Corporation demonstrated the first high-brightness blue LED. Blue light made the first white LED possible, using a phosphor coating to convert part of the blue to lower frequencies and produce white. By the start of the twenty-first century, LED lamps suitable for general lighting were entering the market. In 2009, Philips introduced the first lamps designed to replace the standard 60-watt Edison screw fixture bulb. The solid-state LED had served as an indicator light in consumer electronics and professional audio gear since the 1970s. By the 2000s, efficacy and output had risen enough for LEDs to appear in car headlights and brake lights, flashlights, bicycle lights, and holiday lighting. Indicator LEDs can last up to 100,000 hours, though lighting LEDs run harder and live shorter lives. Their appeal to lighting designers lies in low power consumption, low heat, instantaneous on/off control, steady color over the life of single-color diodes, and low manufacturing cost. Lifetime depends strongly on the diode's temperature, and conditions that raise the internal temperature can sharply shorten it. Some lasers have been adapted as an alternative to LEDs for highly focused illumination.

• 6. Arcs And Discharges

  ›

  Humphry Davy invented the carbon arc around 1805, making it the first practical electric light. It went into commercial use in the 1870s for large buildings and street lighting, until the incandescent light superseded it in the early twentieth century. A carbon arc lamp uses two carbon rod electrodes in open air, fed through a current-limiting ballast. Touching the rod tips and then separating them strikes an arc that produces a white-hot plasma. The lamps beat filament lamps on efficacy, but the carbon rods are short-lived and need constant adjustment as the arc's heat erodes them. They also produce significant ultraviolet output, require ventilation indoors, and need protection from direct sight. Those qualities, high power, high intensity, and a single point source of white light, kept them in movie projectors, stage lighting, and searchlights until after World War II. A discharge lamp shares the core principle but seals two metal electrodes in a glass or silica envelope filled with gas, drawn from neon, argon, xenon, sodium, metal halides, and mercury. Some need very high voltage to strike the arc, supplied by an igniter inside the ballast circuitry, after which the lamp's resistance drops and the ballast limits the current. The most efficient source of electric light is the low-pressure sodium lamp. It gives an almost monochromatic orange-yellow light, which renders any scene in the same single tone, so it is reserved for outdoor public lighting. Astronomers favour it, because its narrow light pollution can be filtered out far more easily than a broadband or continuous spectrum.

• 7. Heat, Hazard, And Waste

  ›

  Just 2 to 5 percent of the energy an incandescent bulb consumes leaves as visible, usable light, while the remaining 95 percent is lost as heat. In warm climates that heat must be removed, adding load to ventilation or air conditioning. In cold weather it carries some value, harnessed deliberately in devices such as heat lamps. The waste explains the worldwide phase-out of incandescent bulbs across the first decades of the twenty-first century, pushed by government regulation and by consumers wanting higher efficiency and longer life. The European Commission estimated in 2012 that a complete ban on incandescent bulbs would add 5 to 10 billion euros to the economy and save 15 billion metric tonnes of carbon dioxide emissions. By 2019, United States electricity usage had fallen for at least five straight years, partly because consumers were swapping incandescents for LEDs. Halogen lamps sit in a separate niche, usually much smaller than standard incandescent lamps because successful operation generally needs a bulb temperature over 200 degrees Celsius. Most use a bulb of fused silica, called quartz, or aluminosilicate glass, often sealed inside an extra layer of glass for safety. That outer layer reduces ultraviolet emission and contains hot shards if the inner envelope explodes. Oily residue from fingerprints can make a hot quartz envelope shatter, as heat builds up at the contaminated spot. Bare bulbs also carry a higher risk of burns or fire, which has led some places to ban them unless enclosed by the luminaire. Lamp life itself is a defined quantity. For many types it is the number of operating hours at which half of them fail, the median life, and production tolerances as low as 1 percent can create a 25 percent variance in lamp life. In the 1900s the Phoebus cartel formed in an attempt to reduce bulb life, a documented example of planned obsolescence.

• 8. Beyond The Bulb

  ›

  The total artificial light from cities, especially street lights, is enough to make them easily visible at night from the air and from space. External lighting grew at 3 to 6 percent through the later half of the twentieth century. It is now the major source of light pollution, and 80 percent of the world's population lives in areas with night-time light pollution, which has been shown to harm some wildlife. Light does work far from streets and ceilings. Electric lamps serve as heat sources in incubators, as infrared lamps in fast food restaurants, and in toys such as the Kenner Easy-Bake Oven. In medicine, lamps deliver light therapy for vitamin D deficiency, skin conditions such as acne and dermatitis, skin cancers, and seasonal affective disorder. Lamps emitting a specific frequency of blue light treat neonatal jaundice, a therapy that began in hospitals and can now be carried out at home. As grow lights, electric lamps aid plant growth, including indoor hydroponics and aquatic plants, with continuing research into the most effective light for the task. The bulb has even become a symbol. In Western culture, an illuminated lightbulb drawn above a person's head signals sudden inspiration. A stylized light bulb serves as the logo of the Turkish AK Party, proof that a device for turning electricity into light now stands in for the spark of an idea itself.