Ten
Electrical light
An electric light, lamp, or light bulb is an electrical component that produces light. It is the most common form of artificial lighting. Lamps usually have a base made of ceramic, metal, glass, or plastic, which secures the lamp in the socket of a light fixture, which is often called a "lamp" as well. The electrical connection to the socket may be made with a screw-thread base, two metal pins, two metal caps or a bayonet mount.
The three main categories of electric lights are incandescent lamps, which produce light by a filament heated white-hot by electric current, gas-discharge lamps, which produce light by means of an electric arc through a gas, such as fluorescent lamps, and LED lamps, which produce light by a flow of electrons across a band gap in a semiconductor.
The energy efficiency of electric lighting has increased radically since the first demonstration of arc lamps and the incandescent light bulb of the 19th century. Modern electric light sources come in a profusion of types and sizes adapted to many applications. Most modern electric lighting is powered by centrally generated electric power, but lighting may also be powered by mobile or standby electric generators or battery systems. Battery-powered light is often reserved for when and where stationary lights fail, often in the form of flashlights or electric lanterns, as well as in vehicles.
History
Before electric lighting became common in the early 20th century, people used candles, gas lights, oil lamps, and fires.[1] Vasily Vladimirovich Petrov developed the first persistent electric arc in 1802, and English chemist Humphry Davy gave a practical demonstration of an arc light in 1806.[2]
In 1840, Warren de la Rue enclosed a platinum coil in a vacuum tube and passed an electric current through it, thus creating one of the world's first electric light bulbs.[3][4][5] The design was based on the concept that the high melting point of platinum would allow it to operate at high temperatures and that the evacuated chamber would contain fewer gas molecules to react with the platinum, improving its longevity. Although it was an efficient design, the cost of the platinum made it impractical for commercial use.[6]
The late 1870s and 1880s were marked by intense competition and innovation, with inventors like Joseph Swan in the UK and Thomas Edison in the US independently developing functional incandescent lamps. This rivalry eventually led to a merger, forming the Edison and Swan Electric Light Company. By the early twentieth century these had completely replaced arc lamps.[7][1]
While the ability of wires to illuminate when supplied with current was first discovered during the Enlightenment, it took more than a century of continuous and incremental improvement, including numerous designs, patents, and resulting intellectual property disputes, until incandescent light bulbs became commercially available in the 1920s.[8][9] The first home to be lit by an electric light was Underhill, the home of Joseph Swan, around 1880.[10]
Types
Incandescent
Main article: Incandescent light bulb
Sign with instructions on the use of light bulbs
A tablet at St John the Baptist Church, Hagley commemorates the installation of electric light in 1934.
In its modern form, the incandescent light bulb consists of a coiled filament of tungsten sealed in a globular glass chamber, either a vacuum or full of an inert gas such as argon. When an electric current is connected, the tungsten is heated to 2,000 to 3,300 K (1,730 to 3,030 °C; 3,140 to 5,480 °F) and glows, emitting light that approximates a continuous spectrum.
Incandescent bulbs are highly inefficient, in that just 2–5% of the energy consumed is emitted as visible, usable light. The remaining 95% is lost as heat.[18] In warmer climates, the emitted heat must then be removed, putting additional pressure on ventilation or air conditioning systems.[19] In colder weather, the heat byproduct has some value, and has been successfully harnessed for warming in devices such as heat lamps. Incandescent bulbs are nonetheless being phased out in favor of technologies like CFLs and LED bulbs in many countries due to their low energy efficiency. The European Commission estimated in 2012 that a complete ban on incandescent bulbs would contribute 5 to 10 billion euros to the economy and save 15 billion metric tonnes of carbon dioxide emissions.[20]
Halogen
Main article: Halogen lamp
Halogen lamps are usually much smaller than standard incandescent lamps, because for successful operation a bulb temperature over 200 °C is generally necessary. For this reason, most have a bulb of fused silica (quartz) or aluminosilicate glass. This is often sealed inside an additional layer of glass. The outer glass is a safety precaution, to reduce ultraviolet emission and to contain hot glass shards should the inner envelope explode during operation.[21] Oily residue from fingerprints may cause a hot quartz envelope to shatter due to excessive heat buildup at the contamination site.[22] The risk of burns or fire is also greater with bare bulbs, leading to their prohibition in some places, unless enclosed by the luminaire.
Those designed for 12- or 24-volt operation have compact filaments, useful for good optical control. Also, they have higher efficacies (lumens per watt) and longer lives than non-halogen types. The light output remains almost constant throughout their life.
Fluorescent
Main article: Fluorescent lamp Top, two compact fluorescent lamps. Bottom, two fluorescent tube lamps. A matchstick, left, is shown for scale. Fluorescent lamps consist of a glass tube that contains mercury vapour or argon under low pressure. Electricity flowing through the tube causes the gases to give off ultraviolet energy. The inside of the tubes are coated with phosphors that give off visible light when struck by ultraviolet photons.[23] They have much higher efficiency than incandescent lamps. For the same amount of light generated, they typically use around one-quarter to one-third the power of an incandescent. The typical luminous efficacy of fluorescent lighting systems is 50–100 lumens per watt, several times the efficacy of incandescent bulbs with comparable light output. Fluorescent lamp fixtures are more costly than incandescent lamps, because they require a ballast to regulate the current through the lamp, but the lower energy cost typically offsets the higher initial cost. Compact fluorescent lamps are available in the same popular sizes as incandescent lamps and are used as an energy-saving alternative in homes. Because they contain mercury, many fluorescent lamps are classified as hazardous waste. The United States Environmental Protection Agency recommends that fluorescent lamps be segregated from general waste for recycling or safe disposal, and some jurisdictions require recycling of them.[24]LED
Main article: LED lamp
LED lamp with E27 Edison screw base
The solid-state light-emitting diode (LED) has been popular as an indicator light in consumer electronics and professional audio gear since the 1970s. In the 2000s, efficacy and output have risen to the point where LEDs are now being used in lighting applications such as car headlights[25] and brake lights,[26] in flashlights[27] and bicycle lights,[28] as well as in decorative applications, such as holiday lighting.[29] Indicator LEDs are known for their extremely long life, up to 100,000 hours, but lighting LEDs are operated much less conservatively, and consequently have shorter lives. LED technology is useful for lighting designers, because of its low power consumption, low heat generation, instantaneous on/off control, and in the case of single color LEDs, continuity of color throughout the life of the diode and relatively low cost of manufacture.[30] LED lifetime depends strongly on the temperature of the diode.[31] Operating an LED lamp in conditions that increase the internal temperature can greatly shorten the lamp's life.
Main article: Arc lamp
The 15 kW xenon short-arc lamp used in the IMAX projection system.
A mercury arc lamp from a fluorescence microscope.
Carbon arc lamps consist of two carbon rod electrodes in open air, supplied by a current-limiting ballast. The electric arc is struck by touching the rod tips then separating them. The ensuing arc produces a white-hot plasma between the rod tips. These lamps have higher efficacy than filament lamps, but the carbon rods are short-lived and require constant adjustment in use, as the intense heat of the arc erodes them.[32] The lamps produce significant ultraviolet output, they require ventilation when used indoors, and due to their intensity they need protection from direct sight.
Invented by Humphry Davy around 1805, the carbon arc was the first practical electric light.[33][34] It was used commercially beginning in the 1870s for large building and street lighting until it was superseded in the early 20th century by the incandescent light.[33] Carbon arc lamps operate at high power and produce high intensity white light. They also are a point source of light. They remained in use in limited applications that required these properties, such as movie projectors, stage lighting, and searchlights, until after World War II.[32]
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| type | working principle | invented | first production | pin configuration |
|---|---|---|---|---|
| Depends on type of light | Luminescence by electricity | 1809; 214 years ago by Humphry Davy (arc lamp) | 1879; 144 years ago by Joseph Swan and Thomas Edison (first demo of incandescent bulb) | Anode and cathode Electronic symbol |
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