Electric light

An electric light, lamp, or light bulb is an electrical device that makes light from electricity. It is the most common kind of artificial lighting. Most lamps have a base made of ceramic, metal, glass, or plastic that holds the lamp in the socket of a light fixture. The lamp may connect to the socket in a few ways, such as a screw-thread base, two metal pins, two metal caps, or a bayonet mount.

There are three main types of electric lights. Incandescent lamps make light when a filament gets very hot from electric current. Gas-discharge lamps make light when an electric arc passes through a gas. Fluorescent lamps are one example. LED lamps make light when electrons move across a band gap in a semiconductor.

The energy efficiency of electric lighting has greatly improved since the first arc lamps and incandescent light bulbs were shown in the 19th century. Today, electric light sources come in many types and sizes for many different uses.

Most modern electric lighting runs on electric power made in central power plants. Lights can also run on mobile or standby generators or on battery systems. Battery-powered lights are often used when and where regular lights fail. They appear as flashlights or electric lanterns, and they are also found in vehicles.

History

Before electric lights became common in the early 20th century, people used candles, gas lights, oil lamps, and fires. In 1799–1800, Alessandro Volta made the voltaic pile, the first electric battery. Its electricity could heat copper wire until it glowed. In 1802, Vasily Vladimirovich Petrov created the first long-lasting electric arc. In 1806, English chemist Humphry Davy showed a working arc light. It took more than a century of steady improvement before commercial light bulbs appeared in the 1920s. In 1840, Warren de la Rue built one of the first electric light bulbs, but its platinum was too expensive for everyday use. William Greener, an English inventor, also made important early contributions with his lamp in 1846.

In the late 1870s and 1880s, inventors such as Joseph Swan in the UK and Thomas Edison in the US made working light bulbs at about the same time. Edison worked to make thinner filaments and better vacuums, which made his bulb more practical. Swan and Edison later joined together to form the Edison and Swan Electric Light Company. This company sold lamps with a new filament that Swan had designed. By the early 20th century, these lamps had completely replaced arc lamps. Later, William D. Coolidge introduced the tungsten filament, which was used in light bulbs for many years. In 1910, Georges Claude introduced the first neon light. In 1934, Arthur Compton reported on successful fluorescent lighting experiments at General Electric Co., Ltd. in Great Britain. A team led by George E. Inman then built a prototype fluorescent lamp at Nela Park in Ohio. The first practical LED arrived in 1962. In 1994, Shuji Nakamura of Nichia Corporation showed the first high-brightness blue LED. In 2009, Philips introduced the first lamps made to replace standard 60 W Edison screw light bulbs. Over the early 21st century, a phase-out of incandescent light bulbs took place around the world. Governments made new rules, and people began to prefer bulbs that use less energy and last longer.

Types

The incandescent light bulb has a coiled tungsten wire inside a glass bulb. When electricity heats the wire, it glows. But only 2–5% of the energy becomes light. The rest is lost as heat. Many countries are moving away from these bulbs and using CFLs and LED bulbs instead. Halogen lamps are usually much smaller than regular incandescent lamps.

Fluorescent lamps use gases in a glass tube and special coatings to make visible light. They use much less power than incandescent lamps for the same amount of light. LEDs were first used as small indicator lights. Today they are used in car lights, flashlights, and decorations. They last a long time, but they wear out faster when they get too hot. The carbon arc was invented by Humphry Davy around 1805. It was the first practical electric light. Gas-discharge lamps send electricity through gas between two metal electrodes. The low-pressure sodium lamp is the most efficient source of electric light. It is mainly used for outdoor street lighting.

Characteristics

Main articles: Incandescent light bulb § Bulb shapes, and Lightbulb socket

Many light bulbs have standard codes and names for their shape and base. For example, some incandescent bulbs are labeled "A19/A60 E26/E27". The "A" part describes the size and shape of the bulb, based on the A-series light bulb. The "E" part describes the size and threads of the Edison screw base. To compare lamps, people often look at luminous flux (measured in lumens), energy consumption (measured in watts), luminous efficacy (lumens per watt), and color temperature (measured in kelvins). A less common measure is the color rendering index (CRI).

For many lamps, life expectancy is the number of hours when half of them have stopped working. This is called the median life. Small differences in how lamps are made can lead to big differences in how long they last. Some lamps stop working early, while others last much longer. For LEDs, life is measured as the time when half of the lamps have lost 70% of their light. In the 1900s, the Phoebus cartel was formed to try to make light bulbs wear out sooner. This is an example of planned obsolescence. Lamps that are switched on and off often, such as those in bathrooms, wear out much sooner than the packaging says. Compact fluorescent lamps are especially affected by this.

Uses

Artificial light, especially from street lights, is so bright that cities can be seen at night from the air and from space. Outdoor lighting grew each year during the second half of the 20th century. It is the main cause of light pollution, which makes it harder for astronomers and others to see the stars. About 80% of the world's people live where there is light pollution at night. Light pollution can harm some wildlife.

Electric lamps can also give off heat. They are used in incubators, as infrared lamps in fast food restaurants, and in toys such as the Kenner Easy-Bake Oven. Lamps are also used for light therapy to help with problems such as vitamin D deficiency, skin problems like acne and dermatitis, skin cancers, and seasonal affective disorder. Lamps that give off a special kind of blue light are used to treat neonatal jaundice. This treatment was first done in hospitals, but it can now be done at home. Electric lamps can also be used as a grow light to help plants grow, especially indoors in hydroponics and for aquatic plants. Researchers are studying which kinds of light work best for plant growth.

Cultural symbolism

In Western culture, a lightbulb, especially one shining above a person's head, stands for a sudden idea.

A simple picture of a light bulb is the logo of the Turkish AK Party.