Anelectric light,lamp, orlight bulb is anelectrical component that produceslight. It is the most common form of artificiallighting. Lamps usually have a base made ofceramic, metal, glass, or plastic that secures them in the socket of alight fixture, which is also commonly referred to as a 'lamp.' The electrical connection to the socket may be made with a screw-thread base, two metal pins, two metal caps or abayonet mount.
Theenergy efficiency of electric lighting has significantly improved since the first demonstrations of arc lamps and incandescent light bulbs in the 19th century. Modern electriclight 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 offlashlights or electriclanterns, as well as in vehicles.
Before electric lighting became common in the early 20th century, people usedcandles,gas lights,oil lamps, andfires.[1] In 1799–1800,Alessandro Volta created thevoltaic pile, the first electric battery. Current from these batteries could heat copper wire to incandescence.Vasily Vladimirovich Petrov developed the first persistentelectric arc in 1802, and English chemistHumphry Davy gave a practical demonstration of anarc light in 1806.[2] It took more than a century of continuous and incremental improvement, including numerous designs, patents, and resulting intellectual property disputes, to get from these early experiments to commercially produced incandescent light bulbs in the 1920s.[3][4]
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 firstelectric light bulbs.[5][6][7] 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.[8]
William Greener, an English inventor, made significant contributions to early electric lighting with his lamp in 1846 (patent specification 11076), laying the groundwork for future innovations such as those by Thomas Edison.
The late 1870s and 1880s were marked by intense competition and innovation, with inventors likeJoseph Swan in the UK andThomas Edison in the US independently developing functional incandescent lamps. Swan's bulbs, based on designs by William Staite, were successful, but the filaments were too thick. Edison worked to create bulbs with thinner filaments, leading to a better design.[9] The rivalry between Swan and Edison eventually led to a merger, forming theEdison and Swan Electric Light Company. By the early twentieth century these had completely replacedarc lamps.[10][1]
The turn of the century saw further improvements in bulb longevity and efficiency, notably with the introduction of the tungsten filament byWilliam D. Coolidge, who applied for a patent in 1912.[11] This innovation became a standard for incandescent bulbs for many years.
In 1910,Georges Claude introduced the first neon light, paving the way for neon signs which would become ubiquitous in advertising.[12][13][14]
In 1934,Arthur Compton, a renowned physicist and GE consultant, reported to the GE lamp department on successful experiments with fluorescent lighting atGeneral Electric Co., Ltd. in Great Britain (unrelated to General Electric in the United States). Stimulated by this report, and with all of the key elements available, a team led by George E. Inman built a prototype fluorescent lamp in 1934 atGeneral Electric'sNela Park (Ohio) engineering laboratory. This was not a trivial exercise; as noted by Arthur A. Bright, "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."[15]
In theUnited States, incandescent light bulbs including halogen bulbs stopped being sold as of August 1, 2023,[needs update] because they do not meet minimum lumens per watt performance metrics established by theU.S. Department of Energy.[17][needs update] Compact fluorescent bulbs are also banned despite their lumens per watt performance because of their toxic mercury that can be released into the home if broken and widespread problems with proper disposal of mercury-containing bulbs.
Sign with instructions on the use of light bulbsA tablet atSt 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 oftungsten sealed in a globular glass chamber, either a vacuum or full of aninert gas such asargon. 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 acontinuous spectrum.
Incandescent bulbs are highly inefficient, in that just 2–5% of the energy consumed is emitted asvisible, usable light. The remaining 95% is lost asheat.[18] In warmer climates, the emitted heat must then be removed, putting additional pressure onventilation orair conditioning systems.[19] In colder weather, the heat byproduct has some value, and has been successfully harnessed for warming in devices such asheat lamps. Incandescent bulbs are nonetheless beingphased out in favor of technologies likeCFLs andLED bulbs in many countries due to their low energy efficiency. TheEuropean 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 ofcarbon dioxide emissions.[20]
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 fromfingerprints 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.
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 withphosphors that give off visible light when struck by ultravioletphotons.[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 typicalluminous 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 aballast to regulate thecurrent 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 anenergy-saving alternative in homes. Because they contain mercury, many fluorescent lamps are classified ashazardous waste. TheUnited States Environmental Protection Agency recommends that fluorescent lamps be segregated from general waste forrecycling or safe disposal, and some jurisdictions require recycling of them.[24]
The solid-statelight-emitting diode (LED) has been popular as an indicator light inconsumer 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,[25] in flashlights[26] and bicycle lights,[27] as well as in decorative applications, such as holiday lighting.[28] 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 forlighting 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.[28] LED lifetime depends strongly on the temperature of the diode.[29] Operating an LED lamp in conditions that increase the internal temperature can greatly shorten the lamp's life. Some lasers have been adapted as an alternative to LEDs to provide highly focused illumination.[30][31]
Carbon arc lamps consist of two carbon rodelectrodes in open air, supplied by a current-limitingballast. Theelectric arc is struck by touching the rod tips then separating them. The ensuing arc produces a white-hotplasma 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 significantultraviolet output, they require ventilation when used indoors, and due to their intensity they need protection from direct sight.
Invented byHumphry 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 asmovie projectors,stage lighting, andsearchlights, until after World War II.[32]
A discharge lamp has a glass or silica envelope containing two metalelectrodes separated by a gas. Gases used include,neon,argon,xenon,sodium,metal halides, andmercury. 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 theelectrical 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, amonochromatic 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 thelight pollution that they generate can be easily filtered, contrary to broadband or continuous spectra.
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/A60E26/E27", a common size for those kinds of light bulbs. In this example, the "A" parameters describe the bulb size and shape within theA-series light bulb while the "E" parameters describe theEdison screw base size and thread characteristics.[35]
Life expectancy for many types of lamp is defined as the number of hours of operation at which 50% of them fail, that is themedian 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 thePhoebus cartel formed in an attempt to reduce the life of electric light bulbs, an example ofplanned obsolescence.[37][38]
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.[39]
The total amount of artificial light (especially fromstreet light) 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 oflight pollution[40] that burdensastronomers[41] and others with 80% of the world's population living in areas with night time light pollution.[42] Light pollution has been shown to have a negative effect on some wildlife.[40][43]
Electric lamps can also be used as agrow light to aid in plant growth[56] especially in indoorhydroponics andaquatic plants with recent research into the most effective types of light for plant growth.[57]
Due to their nonlinear resistance characteristics, tungsten filament lamps have long been used as fast-actingthermistors in electronic circuits. Popular uses have included:
Stabilization of sine wave oscillators
Protection oftweeters inloudspeaker enclosures; excess current that is too high for the tweeter illuminates the light rather than destroying the tweeter.
^Reisert, Sarah (2015)."Let There be Light".Distillations Magazine.1 (3):44–45.Archived from the original on 22 March 2018. Retrieved22 March 2018.
^US 1082933A, William. D. Coolidge, "Tungsten and method of making the same for use as filaments of incandescent electric lamps and for other purposes."
^United States Environmental Protection Agency, OSWER (2015-07-23)."Hazardous Waste".US EPA.Archived from the original on 2015-06-29. Retrieved3 November 2018.
Dark Sacred Night" (2023) is a short science film from the Princeton University Office of Sustainability about lighting obscuring the stars and affecting health and the environment.
