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An electric light, lamp, or light bulb is an
electrical component An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are n ...
that produces
light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 t ...
. It is the most common form of artificial
lighting Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing dayl ...
. Lamps usually have a base made of
ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, ...
, 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 cap A bayonet mount (mainly as a method of mechanical attachment, such as fitting a Photographic lens, lens to a camera using a matching lens mount) or bayonet connector (for electrical use) is a fastener, fastening mechanism consisting of a cyli ...
. The three main categories of electric lights are incandescent lamps, which produce light by a
filament The word filament, which is descended from Latin ''filum'' meaning " thread", is used in English for a variety of thread-like structures, including: Astronomy * Galaxy filament, the largest known cosmic structures in the universe * Solar filament ...
heated white-hot by
electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The movi ...
,
gas-discharge lamp Gas-discharge lamps are a family of artificial light sources that generate light by sending an electric discharge through an ionized gas, a plasma. Typically, such lamps use a noble gas (argon, neon, krypton, and xenon) or a mixture of t ...
s, which produce light by means of an
electric arc An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. ...
through a gas, such as
fluorescent lamp A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet, ult ...
s, and
LED lamp An LED lamp or LED light bulb is an electric light that produces light using light-emitting diodes (LEDs). LED lamps are significantly more energy-efficient than equivalent incandescent lamps and can be significantly more efficient than mo ...
s, which produce light by a flow of electrons across a band gap in a
semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...
. Before electric lighting became common in the early 20th century, people used
candle A candle is an ignitable wick embedded in wax, or another flammable solid substance such as tallow, that provides light, and in some cases, a fragrance. A candle can also provide heat or a method of keeping time. A person who makes candle ...
s, gas lights, oil lamps, and
fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. At a certain point in the combustion reaction, called the ignition point, flames ...
s. Vasily Vladimirovich Petrov developed the first persistent
electric arc An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. ...
in 1802, and English chemist
Humphry Davy Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for ...
gave a practical demonstration of an arc light in 1806. By the 1870s, Davy's arc lamp had been successfully commercialized, and was used to light many public spaces. Efforts by Joseph Swan and
Thomas Edison Thomas Alva Edison (February 11, 1847October 18, 1931) was an American inventor and businessman. He developed many devices in fields such as electric power generation, mass communication, sound recording, and motion pictures. These inventi ...
led to commercial incandescent light bulbs becoming widely available in the 1880s, and by the early twentieth century these had completely replaced
arc lamp An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the first decade of the 1800s, ...
s. 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 Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...
-powered light is often reserved for when and where stationary lights fail, often in the form of
flashlight A flashlight (American English, US, Canadian English, Canada) or torch (British English, UK, Australian English, Australia) is a portable hand-held electric lamp. Formerly, the light source typically was a miniature incandescent light bulb, b ...
s or electric
lantern A lantern is an often portable source of lighting, typically featuring a protective enclosure for the light sourcehistorically usually a candle or a oil lamp, wick in oil, and often a battery-powered light in modern timesto make it easier to ca ...
s, as well as in vehicles.


Types


Incandescent

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. In its modern form, the incandescent light bulb consists of a coiled filament of
tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
sealed in a globular glass chamber, either a vacuum or full of an
inert gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. The noble gases often do not react with many substances and were historically referred to ...
such as
argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice a ...
. 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 In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
. In warmer climates, the emitted heat must then be removed, putting additional pressure on ventilation or
air conditioning Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
systems. 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 The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body ...
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 Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China an ...
.


Halogen

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. Oily residue from
fingerprint A fingerprint is an impression left by the friction ridges of a human finger. The recovery of partial fingerprints from a crime scene is an important method of forensic science. Moisture and grease on a finger result in fingerprints on surfac ...
s may cause a hot quartz envelope to shatter due to excessive heat buildup at the contamination site. 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 better lives than non-halogen types. The light output remains almost constant throughout their life.


Fluorescent

Fluorescent lamp A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet, ult ...
s 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
phosphor A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or v ...
s that give off visible light when struck by ultraviolet
photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alwa ...
s. 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 lamp A compact fluorescent lamp (CFL), also called compact fluorescent light, energy-saving light and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent light bulb; some types fit into light fixtures designed for inca ...
s 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 Hazardous waste is waste that has substantial or potential threats to public health or the environment. Hazardous waste is a type of dangerous goods. They usually have one or more of the following hazardous traits: ignitability, reactivity, cor ...
. The
United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it ...
recommends that fluorescent lamps be segregated from general waste for
recycling Recycling is the process of converting waste materials into new materials and objects. The Energy recycling, recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability t ...
or safe disposal, and some jurisdictions require recycling of them.


LED

The solid-state
light-emitting diode A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
(LED) has been popular as an indicator light in
consumer electronics Consumer electronics or home electronics are electronic ( analog or digital) equipment intended for everyday use, typically in private homes. Consumer electronics include devices used for entertainment, communications and recreation. Usuall ...
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 and brake lights, in flashlights and bicycle lights, as well as in decorative applications, such as holiday lighting. 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. LED lifetime depends strongly on the temperature of the diode. Operating an LED lamp in conditions that increase the internal temperature can greatly shorten the lamp's life.


Carbon arc

Carbon arc lamps consist of two carbon rod
electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials ...
s in open air, supplied by a current-limiting ballast. The
electric arc An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. ...
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. The lamps produce significant
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
output, they require ventilation when used indoors, and due to their intensity they need protection from direct sight. Invented by
Humphry Davy Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for ...
around 1805, the carbon arc was the first practical electric light. 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. 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 projector A movie projector is an opto-mechanical device for displaying motion picture film by projecting it onto a screen. Most of the optical and mechanical elements, except for the illumination and sound devices, are present in movie cameras. Mod ...
s,
stage lighting Stage lighting is the craft of lighting as it applies to the production of theater, dance, opera, and other performance arts.
, and
searchlight A searchlight (or spotlight) is an apparatus that combines an extremely luminosity, bright source (traditionally a carbon arc lamp) with a mirrored parabolic reflector to project a powerful beam of light of approximately parallel rays in a part ...
s, until after World War II.


Discharge

A discharge lamp has a glass or silica envelope containing two metal
electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials ...
s separated by a gas. Gases used include,
neon Neon is a chemical element with the symbol Ne and atomic number 10. It is a noble gas. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air. It was discovered (along with krypt ...
,
argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice a ...
,
xenon Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
,
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
, metal halide, and mercury. The core operating principle is much the same as the carbon arc lamp, but the term "arc lamp" normally refers to carbon arc lamps, with more modern types of gas discharge lamp normally called discharge lamps. With some discharge lamps, very high voltage is used to strike the arc. This requires an electrical circuit called an igniter, which is part of the electrical ballast circuitry. After the arc is struck, the internal resistance of the lamp drops to a low level, and the ballast limits the current to the operating current. Without a ballast, excess current would flow, causing rapid destruction of the lamp. Some lamp types contain a small amount of neon, which permits striking at normal running voltage with no external ignition circuitry. Low-pressure sodium lamps operate this way. The simplest ballasts are just an inductor, and are chosen where cost is the deciding factor, such as street lighting. More advanced electronic ballasts may be designed to maintain constant light output over the life of the lamp, may drive the lamp with a square wave to maintain completely flicker-free output, and shut down in the event of certain faults. The most efficient source of electric light is the low-pressure sodium lamp. It produces, for all practical purposes, a
monochromatic A monochrome or monochromatic image, object or palette is composed of one color (or values of one color). Images using only shades of grey are called grayscale (typically digital) or black-and-white (typically analog). In physics, monochro ...
orange-yellow light, which gives a similarly monochromatic perception of any illuminated scene. For this reason, it is generally reserved for outdoor public lighting applications. Low-pressure sodium lights are favoured for public lighting by astronomers, since the
light pollution Light pollution is the presence of unwanted, inappropriate, or excessive use of artificial lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting, during the day or night. Light po ...
that they generate can be easily filtered, contrary to broadband or continuous spectra.


Form factor

Many lamp units, or light bulbs, are specified in standardized shape codes and socket names. Incandescent bulbs and their retrofit replacements are often specified as " A19/A60 E26/E27", a common size for these kind of light bulbs. In this example, the "A" parameters describe the bulb size and shape within the A-series light bulb while the "E" parameters describe the
Edison screw Edison screw (ES) is a standard lightbulb socket for electric light bulbs. It was developed by Thomas Edison (1847–1931), patented in 1881, and was licensed in 1909 under General Electric's Mazda trademark. The bulbs have right-hand threaded ...
base size and thread characteristics.


Life expectancy

Life expectancy for many types of lamp is defined as the number of hours of operation at which 50% of them fail, that is the
median In statistics and probability theory, the median is the value separating the higher half from the lower half of a data sample, a population, or a probability distribution. For a data set, it may be thought of as "the middle" value. The basic f ...
life of the lamps. Production tolerances as low as 1% can create a variance of 25% in lamp life, so in general some lamps will fail well before the rated life expectancy, and some will last much longer. For LEDs, lamp life is defined as the operation time at which 50% of lamps have experienced a 70% decrease in light output. In the 1900s the Phoebus cartel formed in an attempt to reduce the life of electric light bulbs, an example of planned obsolescence. Some types of lamp are also sensitive to switching cycles. Rooms with frequent switching, such as bathrooms, can expect much shorter lamp life than what is printed on the box. Compact fluorescent lamps are particularly sensitive to switching cycles.


Uses

The total amount of artificial light (especially from
street light A street light, light pole, lamp pole, lamppost, street lamp, light standard, or lamp standard is a raised source of light on the edge of a road or path. Similar lights may be found on a railway platform. When urban electric power distribution ...
) is sufficient for cities to be easily visible at night from the air, and from space. External lighting grew at a rate of 3-6 percent for the later half of the 20th century and is the major source of
light pollution Light pollution is the presence of unwanted, inappropriate, or excessive use of artificial lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting, during the day or night. Light po ...
that burdens
astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...
s and others with 80% of the world's population living in areas with night time light pollution. Light pollution has been shown to have a negative effect on some wildlife. Electric lamps can be used as heat sources, for example in incubators, as
infrared lamp Infrared lamps are electrical devices which emit infrared radiation. Infrared lamps are commonly used in radiant heating for industrial processes and building heating. Infrared LEDs are used for communication over optical fibers and in remote c ...
s in
fast food Fast food is a type of mass-produced food designed for commercial resale, with a strong priority placed on speed of service. It is a commercial term, limited to food sold in a restaurant or store with frozen, preheated or precooked ingredie ...
restaurants and toys such as the Kenner Easy-Bake Oven. Lamps can also be used for light therapy to deal with such issues as vitamin D deficiency, skin conditions such as
acne Acne, also known as ''acne vulgaris'', is a long-term skin condition that occurs when dead skin cells and oil from the skin clog hair follicles. Typical features of the condition include blackheads or whiteheads, pimples, oily skin, and ...
and
dermatitis Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved c ...
, skin cancers, and seasonal affective disorder. Lamps which emit a specific frequency of blue light are also used to treat
neonatal jaundice Neonatal jaundice is a yellowish discoloration of the white part of the eyes and skin in a newborn baby due to high bilirubin levels. Other symptoms may include excess sleepiness or poor feeding. Complications may include seizures, cerebral pal ...
with the treatment which was initially undertaken in hospitals being able to be conducted at home. Electric lamps can also be used as a grow light to aid in plant growth especially in indoor hydroponics and
aquatic plants Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that g ...
with recent research into the most effective types of light for plant growth. Due to their nonlinear resistance characteristics, tungsten filament lamps have long been used as fast-acting
thermistor A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word thermistor is a portmanteau of ''thermal'' and ''resistor''. Thermistors are divided based on their conduction ...
s in electronic circuits. Popular uses have included: * Stabilization of sine wave oscillators * Protection of tweeters in loudspeaker enclosures; excess current that is too high for the tweeter illuminates the light rather than destroying the tweeter. *
Automatic volume control Automatic gain control (AGC) is a closed-loop feedback regulating circuit in an amplifier or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the inpu ...
in telephones


Circuit symbols

In circuit diagrams, lamps have two main types of symbols, indicating their respective functions. These are: File:Lamp symbol.svg, The cross in a circle usually represents a lamp as an indicator. (ANSI/IEEE Std 315A-1986) File:Lamp symbol, old.svg, The semicircular dent in a circle, which usually represents a lamp as a source of light or illumination.


Cultural symbolism

In Western culture, a lightbulb — in particular, the appearance of an illuminated lightbulb above a person's head — signifies sudden inspiration.


See also

* Light tube * List of light sources *
Flameless candle Flameless candles are an electronic alternative to traditional wick candles. They are typically utilized as aesthetic lighting devices and come in a variety of shapes, colors and sizes. A flame-effect lightbulb contains multiple small light-emittin ...


References

{{DEFAULTSORT:Electric Light
Light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 t ...
Lighting