Fluorescent lamp

Fluorescent lamps

Top, two compact uorescent lamps. Bottom, two uorescenttube lamps. A matchstick, left, is shown for scale.

Compact uorescent lamp with electronic ballast

A uorescent lamp or a uorescent tube is a lowpressure mercury-vapor gas-discharge lamp that usesuorescence to produce visible light. An electric currentin the gas excites mercury vapor which produces short-wave ultraviolet light that then causes a phosphor coatingon the inside of the bulb to glow. A uorescent lamp

Typical F71T12 100 W bi-pin lamp used in tanning beds. The(Hg) symbol indicates that this lamp contains mercury. In the US,this symbol is now required on all uorescent lamps that containmercury.[1]

One style of lamp holder for T12 and T8 bi pin uorescent lamps

converts electrical energy into useful light much more ef-ciently than incandescent lamps. The luminous ecacyof a uorescent light bulb can exceed 100 lumens perwatt, several times the ecacy of an incandescent bulbwith comparable light output.

1

2 1 HISTORY

Inside the lamp end of a preheat bi-pin lamp. In this lamp thelament is surrounded by an oblong metal cathode shield, whichhelps reduce lamp end darkening.[2]

Fluorescent lamp xtures are more costly than incandes-cent lamps because they require a ballast to regulate thecurrent through the lamp, but the lower energy cost typ-ically osets the higher initial cost. Compact uorescentlamps are now available in the same popular sizes as in-candescents and are used as an energy-saving alternativein homes.Because they contain mercury, many uorescent lampsare classied as hazardous waste. The United States En-vironmental Protection Agency recommends that uores-cent lamps be segregated from general waste for recyclingor safe disposal.[3]

1 History

1.1 Physical discoveries

Fluorescence of certain rocks and other substances hadbeen observed for hundreds of years before its naturewas understood. By the middle of the 19th century, ex-perimenters had observed a radiant glow emanating frompartially evacuated glass vessels through which an electriccurrent passed. One of the rst to explain it was the Irishscientist Sir George Stokes from the University of Cam-bridge, who named the phenomenon uorescence afteruorite, a mineral many of whose samples glow stronglydue to impurities. The explanation relied on the natureof electricity and light phenomena as developed by theBritish scientists Michael Faraday in the 1840s and JamesClerk Maxwell in the 1860s.[4]

Little more was done with this phenomenon until 1856when a German glassblower named Heinrich Geisslercreated a mercury vacuum pump that evacuated a glasstube to an extent not previously possible. When an elec-

trical current passed through a Geissler tube, a stronggreen glow on the walls of the tube at the cathode endcould be observed. Because it produced some beautifullight eects, the Geissler tube was a popular source ofamusement. More important, however, was its contribu-tion to scientic research. One of the rst scientists to ex-periment with a Geissler tube was Julius Plcker who sys-tematically described in 1858 the luminescent eects thatoccurred in a Geissler tube. He also made the importantobservation that the glow in the tube shifted position whenin proximity to an electromagnetic eld. Alexandre Ed-mond Becquerel observed in 1859 that certain substancesgave o light when they were placed in a Geissler tube.He went on to apply thin coatings of luminescent materi-als to the surfaces of these tubes. Fluorescence occurred,but the tubes were very inecient and had a short oper-ating life.[5]

Inquiries that began with the Geissler tube continued aseven better vacuums were produced. The most famouswas the evacuated tube used for scientic research byWilliam Crookes. That tube was evacuated by the highlyeective mercury vacuum pump created by HermannSprengel. Research conducted by Crookes and others ul-timately led to the discovery of the electron in 1897 byJ. J. Thomson and X-rays in 1895 by Wilhelm Roentgen.But the Crookes tube, as it came to be known, producedlittle light because the vacuum in it was too good and thuslacked the trace amounts of gas that are needed for elec-trically stimulated luminescence.

1.2 Early discharge lamps

While Becquerel was interested primarily in conduct-ing scientic research into uorescence, Thomas Edisonbriey pursued uorescent lighting for its commercial po-tential. He invented a uorescent lamp in 1896 that used acoating of calcium tungstate as the uorescing substance,excited by X-rays, but although it received a patent in1907,[6] it was not put into production. As with a fewother attempts to use Geissler tubes for illumination, ithad a short operating life, and given the success of theincandescent light, Edison had little reason to pursue analternative means of electrical illumination. Nikola Teslamade similar experiments in the 1890s, devising high-frequency powered uorescent bulbs that gave a brightgreenish light, but as with Edisons devices, no commer-cial success was achieved.Although Edison lost interest in uorescent lighting, oneof his former employees was able to create a gas-basedlamp that achieved a measure of commercial success. In1895 Daniel McFarlan Moore demonstrated lamps 2 to3 meters (6.6 to 9.8 ft) in length that used carbon diox-ide or nitrogen to emit white or pink light, respectively.As with future uorescent lamps, they were considerablymore complicated than an incandescent bulb.[7]

After years of work, Moore was able to extend the op-

1.2 Early discharge lamps 3

One of the rst mercury vapor lamps invented by Peter CooperHewitt, 1903. It was similar to a uorescent lamp without theuorescent coating on the tube, and produced greenish light. Theround device under the lamp is the ballast.

erating life of the lamps by inventing an electromag-netically controlled valve that maintained a constant gaspressure within the tube.[8] Although Moores lamp wascomplicated, was expensive to install, and required veryhigh voltages, it was considerably more ecient than in-candescent lamps, and it produced a closer approxima-tion to natural daylight than contemporary incandescentlamps. From 1904 onwards Moores lighting system wasinstalled in a number of stores and oces.[9] Its successcontributed to General Electrics motivation to improvethe incandescent lamp, especially its lament. GEs ef-forts came to fruition with the invention of a tungsten-based lament. The extended lifespan and improved ef-cacy of incandescent bulbs negated one of the key ad-vantages of Moores lamp, but GE purchased the rele-vant patents in 1912. These patents and the inventive ef-forts that supported themwere to be of considerable valuewhen the rm took up uorescent lighting more than twodecades later.At about the same time that Moore was developing hislighting system, another American was creating a meansof illumination that also can be seen as a precursor to themodern uorescent lamp. This was the mercury-vaporlamp, invented by Peter Cooper Hewitt and patented in

Peter Cooper Hewitt

1901 (US 682692; this patent number is frequently mis-quoted as US 889,692). Hewitts lamp glowed whenan electric current was passed through mercury vapor ata low pressure. Unlike Moores lamps, Hewitts weremanufactured in standardized sizes and operated at lowvoltages. The mercury-vapor lamp was superior to theincandescent lamps of the time in terms of energy ef-ciency, but the blue-green light it produced limited itsapplications. It was, however, used for photography andsome industrial processes.Mercury vapor lamps continued to be developed at a slowpace, especially in Europe, and by the early 1930s they re-ceived limited use for large-scale illumination. Some ofthem employed uorescent coatings, but these were usedprimarily for color correction and not for enhanced lightoutput. Mercury vapor lamps also anticipated the uores-cent lamp in their incorporation of a ballast to maintain aconstant current.Cooper-Hewitt had not been the rst to use mercury va-por for illumination, as earlier eorts had been mountedby Way, Rapie, Arons, and Bastian and Salisbury. Ofparticular importance was the mercury vapor lamp in-vented by Kch in Germany. This lamp used quartz inplace of glass to allow higher operating temperatures, andhence greater eciency. Although its light output relativeto electrical consumption was better than that of othersources of light, the light it produced was similar to thatof the Cooper-Hewitt lamp in that it lacked the red por-tion of the spectrum, making it unsuitable for ordinarylighting.

4 1 HISTORY

1.3 Neon lamps

Main article: Neon lighting

The next step in gas-based lighting took advantage ofthe luminescent qualities of neon, an inert gas that hadbeen discovered in 1898 by isolation from the atmo-sphere. Neon glowed a brilliant red when used in Geisslertubes.[10] By 1910, Georges Claude, a Frenchman whohad developed a technology and a successful business forair liquefaction, was obtaining enough neon as a byprod-uct to support a neon lighting industry.[11][12] While neonlighting was used around 1930 in France for general il-lumination, it was no more energy-ecient than conven-tional incandescent lighting. Neon tube lighting, whichalso includes the use of argon and mercury vapor as al-ternate gases, came to be used primarily for eye-catchingsigns and advertisements. Neon lighting was relevantto the development of uorescent lighting, however, asClaudes improved electrode (patented in 1915) over-came sputtering, a major source of electrode degrada-tion. Sputtering occurred when ionized particles struckan electrode and tore o bits of metal. Although Claudesinvention required electrodes with a lot of surface area,it showed that a major impediment to gas-based lightingcould be overcome.The development of the neon light also was signicantfor the last key element of the uorescent lamp, its uo-rescent coating. In 1926 Jacques Risler received a Frenchpatent for the application of uorescent coatings to neonlight tubes.[9] The main use of these lamps, which can beconsidered the rst commercially successful uorescents,was for advertising, not general illumination. This, how-ever, was not the rst use of uorescent coatings; Edisonused calcium tungstate for his unsuccessful lamp. Othereorts had been mounted, but all were plagued by loweciency and various technical problems. Of particularimportance was the invention in 1927 of a low-voltagemetal vapor lamp by Friedrich Meyer, Hans-JoachimSpanner, and Edmund Germer, who were employees ofa German rm in Berlin. A German patent was grantedbut the lamp never went into commercial production.

1.4 Commercialization of uorescentlamps

All the major features of uorescent lighting were inplace at the end of the 1920s. Decades of invention anddevelopment had provided the key components of uo-rescent lamps: economically manufactured glass tubing,inert gases for lling the tubes, electrical ballasts, long-lasting electrodes, mercury vapor as a source of lumines-cence, eective means of producing a reliable electricaldischarge, and uorescent coatings that could be ener-gized by ultraviolet light. At this point, intensive devel-opment was more important than basic research.

In 1934, Arthur Compton, a renowned physicist and GEconsultant, reported to the GE lamp department on suc-cessful experiments with uorescent lighting at GeneralElectric Co., Ltd. in Great Britain (unrelated to GeneralElectric in the United States). Stimulated by this report,and with all of the key elements available, a team led byGeorge E. Inman built a prototype uorescent lamp in1934 at General Electrics Nela Park (Ohio) engineeringlaboratory. This was not a trivial exercise; as noted byArthur A. Bright, A great deal of experimentation hadto be done on lamp sizes and shapes, cathode construc-tion, gas pressures of both argon and mercury vapor, col-ors of uorescent powders, methods of attaching themto the inside of the tube, and other details of the lampand its auxiliaries before the new device was ready forthe public.[9]

In addition to having engineers and technicians along withfacilities for R&D work on uorescent lamps, GeneralElectric controlled what it regarded as the key patentscovering uorescent lighting, including the patents orig-inally issued to Hewitt, Moore, and Kch. More impor-tant than these was a patent covering an electrode thatdid not disintegrate at the gas pressures that ultimatelywere employed in uorescent lamps. Albert W. Hull ofGEs Schenectady Research Laboratory led for a patenton this invention in 1927, which was issued in 1931.[13]General Electric used its control of the patents to pre-vent competition with its incandescent lights and prob-ably delayed the introduction of uorescent lighting by20 years. Eventually, war production required 24-hourfactories with economical lighting and uorescent lightsbecame available.While the Hull patent gave GE a basis for claiming legalrights over the uorescent lamp, a few months after thelamp went into production the rm learned of a U.S.patent application that had been led in 1927 for theaforementioned metal vapor lamp invented in Germanyby Meyer, Spanner, and Germer. The patent applicationindicated that the lamp had been created as a superiormeans of producing ultraviolet light, but the applicationalso contained a few statements referring to uorescent il-lumination. Eorts to obtain a U.S. patent had met withnumerous delays, but were it to be granted, the patentmight have caused serious diculties for GE. At rst,GE sought to block the issuance of a patent by claimingthat priority should go to one of their employees, LeroyJ. Buttolph, who according to their claim had inventeda uorescent lamp in 1919 and whose patent applicationwas still pending. GE also had led a patent applicationin 1936 in Inmans name to cover the improvementswrought by his group. In 1939 GE decided that the claimof Meyer, Spanner, and Germer had some merit, and thatin any event a long interference procedure was not in theirbest interest. They therefore dropped the Buttolph claimand paid $180,000 to acquire the Meyer, et al. applica-tion, which at that point was owned by a rm known asElectrons, Inc. The patent was duly awarded in December

2.1 Construction 5

1939.[14] This patent, along with the Hull patent, put GEon what seemed to be rm legal ground, although it facedyears of legal challenges from Sylvania Electric Products,Inc., which claimed infringement on patents that it held.Even though the patent issue would not be completely re-solved for many years, General Electrics strength inman-ufacturing and marketing the bulb gave it a pre-eminentposition in the emerging uorescent light market. Sales ofuorescent lumiline lamps commenced in 1938 whenfour dierent sizes of tubes were put on the market usedin xtures manufactured by three leading corporations,Lightolier, Artcraft Fluorescent Lighting Corporation,and Globe Lighting, two based in NewYork City. Duringthe following year GE and Westinghouse publicized thenew lights through exhibitions at the New York WorldsFair and the Golden Gate International Exposition in SanFrancisco. Fluorescent lighting systems spread rapidlyduring World War II as wartime manufacturing intensi-ed lighting demand. By 1951 more light was producedin the United States by uorescent lamps than by incan-descent lamps.[15]

In the rst years zinc orthosilicate with varying contentof beryllium was used as greenish phosphor. Small ad-ditions of magnesium tungstate improved the blue partof the spectrum yielding acceptable white. After it wasdiscovered that beryllium was toxic, halophosphate basedphosphors took over.[16]

2 Principles of operation

The fundamental means for conversion of electrical en-ergy into radiant energy in a uorescent lamp relies oninelastic scattering of electrons when an incident electroncollides with an atom in the gas. If the (incident) freeelectron has enough kinetic energy, it transfers energy tothe atoms outer electron, causing that electron to tem-porarily jump up to a higher energy level. The collisionis 'inelastic' because a loss of kinetic energy occurs.This higher energy state is unstable, and the atom willemit an ultraviolet photon as the atoms electron re-verts to a lower, more stable, energy level. Most of thephotons that are released from the mercury atoms havewavelengths in the ultraviolet (UV) region of the spec-trum, predominantly at wavelengths of 253.7 and 185nanometers (nm). These are not visible to the human eye,so they must be converted into visible light. This is doneby making use of uorescence. Ultraviolet photons areabsorbed by electrons in the atoms of the lamps interioruorescent coating, causing a similar energy jump, thendrop, with emission of a further photon. The photon thatis emitted from this second interaction has a lower energythan the one that caused it. The chemicals that make upthe phosphor are chosen so that these emitted photons areat wavelengths visible to the human eye. The dierencein energy between the absorbed ultra-violet photon and

the emitted visible light photon goes toward heating upthe phosphor coating.When the light is turned on, the electric power heats upthe cathode enough for it to emit electrons (thermionicemission). These electrons collide with and ionize noblegas atoms inside the bulb surrounding the lament to forma plasma by the process of impact ionization. As a resultof avalanche ionization, the conductivity of the ionizedgas rapidly rises, allowing higher currents to ow throughthe lamp.The ll gas helps determine the operating electrical char-acteristics of the lamp, but does not give o light itself.The ll gas eectively increases the distance that elec-trons travel through the tube, which allows an electron agreater chance of interacting with a mercury atom. Ar-gon atoms, excited to a metastable state by impact of anelectron, can impart this energy to a neutral mercury atomand ionize it, described as the Penning eect. This has thebenet of lowering the breakdown and operating voltageof the lamp, compared to other possible ll gases such askrypton.[17]

2.1 Construction

Close-up of the cathodes of a germicidal lamp (an essentiallysimilar design that uses no uorescent phosphor, allowing theelectrodes to be seen.)

A uorescent lamp tube is lled with a gas contain-ing low pressure mercury vapor and argon, xenon, neon,or krypton. The pressure inside the lamp is around0.3% of atmospheric pressure.[18] The inner surfaceof the lamp is coated with a uorescent (and often

6 2 PRINCIPLES OF OPERATION

slightly phosphorescent) coating made of varying blendsof metallic and rare-earth phosphor salts. The lampselectrodes are typically made of coiled tungsten and usu-ally referred to as cathodes because of their prime func-tion of emitting electrons. For this, they are coated with amixture of barium, strontium and calcium oxides chosento have a low thermionic emission temperature.

The unltered ultraviolet glow of a germicidal lamp is producedby a low pressure mercury vapor discharge (identical to that in auorescent lamp) in an uncoated fused quartz envelope.

Fluorescent lamp tubes are typically straight and rangein length from about 100 millimeters (3.9 in) for minia-ture lamps, to 2.43 meters (8.0 ft) for high-output lamps.Some lamps have the tube bent into a circle, used for tablelamps or other places where a more compact light sourceis desired. Larger U-shaped lamps are used to providethe same amount of light in a more compact area, and areused for special architectural purposes. Compact uores-cent lamps have several small-diameter tubes joined in abundle of two, four, or six, or a small diameter tube coiledinto a helix, to provide a high amount of light output in

little volume.Light-emitting phosphors are applied as a paint-like coat-ing to the inside of the tube. The organic solvents areallowed to evaporate, then the tube is heated to nearlythe melting point of glass to drive o remaining organiccompounds and fuse the coating to the lamp tube. Care-ful control of the grain size of the suspended phosphors isnecessary; large grains, 35 micrometers or larger, lead toweak grainy coatings, whereas too many small particles1 or 2 micrometers or smaller leads to poor light mainte-nance and eciency. Most phosphors perform best witha particle size around 10 micrometers. The coating mustbe thick enough to capture all the ultraviolet light pro-duced by the mercury arc, but not so thick that the phos-phor coating absorbs too much visible light. The rstphosphors were synthetic versions of naturally occurringuorescent minerals, with small amounts of metals addedas activators. Later other compounds were discovered,allowing diering colors of lamps to be made.[19]

2.2 Electrical aspects of operation

Dierent ballasts for uorescent and discharge lamps

Fluorescent lamps are negative dierential resistance de-vices, so as more current ows through them, the elec-trical resistance of the uorescent lamp drops, allowingfor even more current to ow. Connected directly to aconstant-voltage power supply, a uorescent lamp wouldrapidly self-destruct due to the uncontrolled current ow.To prevent this, uorescent lamps must use an auxiliarydevice, a ballast, to regulate the current ow through thelamp.The terminal voltage across an operating lamp varies de-pending on the arc current, tube diameter, temperature,and ll gas. A xed part of the voltage drop is due tothe electrodes. A general lighting service 48-inch (1,219mm) T12[20] lamp operates at 430 mA, with 100 voltsdrop. High output lamps operate at 800 mA, and sometypes operate up to 1.5 A. The power level varies from 33to 82 watts per meter of tube length (10 to 25 W/ft) forT12 lamps.[21]

2.4 Losses 7

The simplest ballast for alternating current (AC) use isan inductor placed in series, consisting of a winding on alaminated magnetic core. The inductance of this windinglimits the ow of AC current. This type is still used, forexample, in 120 volt operated desk lamps using relativelyshort lamps. Ballasts are rated for the size of lamp andpower frequency. Where the AC voltage is insucient tostart long uorescent lamps, the ballast is often a step-upautotransformer with substantial leakage inductance (soas to limit the current ow). Either form of inductiveballast may also include a capacitor for power factor cor-rection.

230 V ballast for 1820 W

Many dierent circuits have been used to operate uo-rescent lamps. The choice of circuit is based on AC volt-age, tube length, initial cost, long term cost, instant versusnon-instant starting, temperature ranges and parts avail-ability, etc.Fluorescent lamps can run directly from a direct current(DC) supply of sucient voltage to strike an arc. The bal-last must be resistive, and would consume about as muchpower as the lamp. When operated from DC, the start-ing switch is often arranged to reverse the polarity of thesupply to the lamp each time it is started; otherwise, themercury accumulates at one end of the tube. Fluores-cent lamps are (almost) never operated directly from DCfor those reasons. Instead, an inverter converts the DCinto AC and provides the current-limiting function as de-scribed below for electronic ballasts.

2.3 Eect of temperature

The light output and performance of uorescent lamps iscritically aected by the temperature of the bulb wall andits eect on the partial pressure of mercury vapor withinthe lamp.[19] Each lamp contains a small amount of mer-cury, which must vaporize to support the lamp currentand generate light. At low temperatures the mercury is inthe form of dispersed liquid droplets. As the lampwarms,more of the mercury is in vapor form. At higher tempera-tures, self-absorption in the vapor reduces the yield ofUV

Thermal image of a helical uorescent lamp.

and visible light. Since mercury condenses at the coolestspot in the lamp, careful design is required to maintainthat spot at the optimum temperature, around 40 C (104F).By using an amalgam with some other metal, the vaporpressure is reduced and the optimum temperature rangeextended upward; however, the bulb wall cold spot tem-perature must still be controlled to prevent migration ofthe mercury out of the amalgam and condensing on thecold spot. Fluorescent lamps intended for higher outputwill have structural features such as a deformed tube orinternal heat-sinks to control cold spot temperature andmercury distribution. Heavily loaded small lamps, suchas compact uorescent lamps, also include heat-sink ar-eas in the tube to maintain mercury vapor pressure at theoptimum value.[22]

2.4 Losses

40 watts power in

Ballast 90%

Electrodes 92%

Discharge 85%

Phosphor 86%

Quantum efficiency 45%

11 w

Visible lightout

4 w Ballast loss

3 w Electrode loss

5 w Not visible or UV

4 w UV photons lost

13 w Quantum efficiency5.5 ev UV to 2.5 ev visible

Losses in a 36 w t8 tri-phosphor fluorescent lamp with electronic ballast

A Sankey diagram of energy losses in a uorescent lamp. Inmod-ern designs, the biggest loss is the quantum eciency of convert-ing high-energy UV photons to lower-energy visible light photons.

8 2 PRINCIPLES OF OPERATION

Only a fraction of the electrical energy input into a lampis converted to useful light. The ballast dissipates someheat; electronic ballasts may be around 90% ecient. Axed voltage drop occurs at the electrodes, which alsoproduces heat. Some of the energy in the mercury va-por column is also dissipated, but about 85% is turnedinto visible and ultraviolet light.The UV light is absorbed by the lamps uorescent coat-ing, which re-radiates the energy at longer wavelengthsto emit visible light. Not all the UV energy striking thephosphor gets converted into visible light. In a modernlamp, for every 100 incident photons of UV impactingthe phosphor, only 86 visible light photons are emitted(a quantum eciency of 86%). The largest single loss inmodern lamps is due to the lower energy of each photonof visible light, compared to the energy of the UV pho-tons that generated them (a phenomenon called Stokesshift). Incident photons have an energy of 5.5 electronvolts but produce visible light photons with energy around2.5 electron volts, so only 45% of the UV energy is used;the rest is dissipated as heat. If a so-called two-photonphosphor could be developed, this would improve theeciency but much research has not yet found such asystem.[23]

2.5 Cold cathode lamps

Most uorescent lamps use electrodes that operate bythermionic emission, meaning they are operated at a highenough temperature for the electrode material (usuallyaided by a special coating) to emit electrons into the tubeby heat.However, there are also tubes that operate in cold cath-ode mode, whereby electrons are liberated into the tubeonly by the large potential dierence (voltage) betweenthe electrodes. This does not mean the electrodes are cold(indeed, they can be very hot), but it does mean they areoperating below their thermionic emission temperature.Because cold cathode lamps have no thermionic emis-sion coating to wear out they can have much longer livesthan hot cathode tubes. This quality makes them desir-able for maintenance-free long-life applications (such asbacklights in liquid crystal displays). Sputtering of theelectrode may still occur, but electrodes can be shaped(e.g. into an internal cylinder) to capturemost of the sput-tered material so it is not lost from the electrode.Cold cathode lamps are generally less ecient thanthermionic emission lamps because the cathode fall volt-age is much higher. The increased fall voltage results inmore power dissipation at tube ends, which does not con-tribute to light output. However, this is less signicantwith longer tubes. The increased power dissipation attube ends also usually means cold cathode tubes have tobe run at a lower loading than their thermionic emissionequivalents. Given the higher tube voltage required any-way, these tubes can easily be made long, and even run

as series strings. They are better suited for bending intospecial shapes for lettering and signage, and can also beinstantly switched on or o.

2.6 Starting

The mercury atoms in the uorescent tube must be ion-ized before the arc can strike within the tube. For smalllamps, it does not take much voltage to strike the arc andstarting the lamp presents no problem, but larger tubesrequire a substantial voltage (in the range of a thousandvolts).

A

ED

F

C

B

G

F

A preheat uorescent lamp circuit using an automatic startingswitch. A: Fluorescent tube, B: Power (+220 volts), C: Starter,D: Switch (bi-metallic thermostat), E: Capacitor, F: Filaments,G: Ballast

Starting a preheat lamp. The automatic starter switch ashesorange each time it attempts to start the lamp.

2.6.1 Preheating

This technique uses a combination lamentcathode ateach end of the lamp in conjunction with a mechanicalor automatic (bi-metallic) switch (see circuit diagram tothe right) that initially connect the laments in series withthe ballast to preheat them; when the arc is struck the la-ments are disconnected. This system is described as pre-heat in some countries and switchstart in others.[24] These

2.6 Starting 9

systems are standard equipment in 200240 V countries(and for 100120 V lamps up to about 30 watts).

A preheat uorescent lamp starter (automatic starting switch)

Before the 1960s four-pin thermal starters and manualswitches were used. Amethod widely used for preheatingfrom then, and still in common use, is a glow starter (illus-trated). It consists of a normally open bi-metallic switchin a small sealed inert gas (neon or argon) gas-dischargelamp.

Electronic uorescent lamp starters

When power is rst applied to the circuit, there will be aglow discharge across the electrodes in the starter lamp.This heats the gas in the starter and causes one of thebi-metallic contacts to bend towards the other. Whenthe contacts touch, the two laments of the uorescentlamp and the ballast will eectively be switched in se-ries to the supply voltage. The current through the l-aments causes them to heat up and emit electrons intothe tube gas by thermionic emission. In the starter, thetouching contacts short out the voltage sustaining the glowdischarge, extinguishing it so the gas cools down and nolonger heats the bi-metallic switch, which opens withina second or two. The current through the laments andthe inductive ballast is abruptly interrupted, leaving thefull line voltage applied between the laments at the endsof the tube and generating an inductive kick which pro-vides the high voltage needed to start the lamp. The lamp

will fail to strike if the laments are not hot enough, inwhich case the cycle repeats; several cycles are usuallyneeded, which causes ickering and clicking during start-ing (older thermal starters behaved better in this respect).A power factor correction (PFC) capacitor draws lead-ing current from the mains to compensate for the laggingcurrent drawn by the lamp circuit.[24]

Once the tube strikes, the impinging main dischargekeeps the cathodes hot, permitting continued electronemission without the need for the laments to continueto be heated. The starter switch does not close again be-cause the voltage across the lit tube is insucient to starta glow discharge in the starter.[24]

With automated starters such as glow starters, a failingtube will cycle endlessly, ickering as the lamp quicklygoes out because the emission mix is insucient to keepthe lamp current high enough to keep the glow starteropen. This runs the ballast at higher temperature. Somemore advanced starters time out in this situation, and donot attempt repeated starts until power is reset. Someolder systems used a thermal over-current trip to de-tect repeated starting attempts and disable the circuit un-til manually reset. The switch contacts in glow startersare subject to wear and inevitably fail eventually, so thestarter is manufactured as a plug-in replaceable unit.More recently introduced electronic starters use a dier-ent method to preheat the cathodes.[25] They may be de-signed to be plug-in interchangeable with glow starters foruse in standard ttings. They commonly use a purpose-designed semiconductor switch and soft start the lampby preheating the cathodes before applying a controlledstarting pulse which strikes the lamp rst time withoutickering; this dislodges a minimal amount of materialfrom the cathodes during starting, giving longer lamp lifethan possible with the uncontrolled impulses to which thelamp is subjected in a switchstart.[24] This is claimed toprolong lamp life by a factor of typically 3 to 4 times fora lamp frequently switched on as in domestic use,[26] andto reduce the blackening of the ends of the lamp typicalof uorescent tubes. The circuit is typically complex, butthe complexity is built into the IC. Electronic starters maybe optimized for fast starting (typical start time of 0.3seconds),[26][27] or for most reliable starting even at lowtemperatures and with low supply voltages, with a startuptime of 24 seconds.[28] The faster-start units may pro-duce audible noise during start-up.[29]

Electronic starters only attempt to start a lamp for a shorttime when power is initially applied, and do not repeat-edly attempt to restrike a lamp that is dead and unableto sustain an arc; some automatically shut down a failedlamp.[25] This eliminates the re-striking of a lamp andthe continuous ickering of a failing lamp with a glowstarter. Electronic starters are not subject to wear anddo not need replacing periodically, although they mayfail like any other electronic circuit. Manufacturers typ-ically quote lives of 20 years, or as long as the light

10 2 PRINCIPLES OF OPERATION

tting.[27][28] Starters are inexpensive, typically less than50 US cents for the short-lived glow type (dependingupon lamp power), and perhaps ten times more for theelectronic type as of 2013.

2.6.2 Instant start

Another type of tube does not have laments to start itat all. Instant start uorescent tubes simply use a highenough voltage to break down the gas and mercury col-umn and thereby start arc conduction. These tubes can beidentied by a single pin at each end of the tube. The lampholders have a disconnect socket at the low-voltage endwhich disconnects the ballast when the tube is removed,to prevent electric shock. Low-cost lighting xtures withan integrated electronic ballast use instant start on lampsdesigned for preheating, although it shortens lamp life.

2.6.3 Rapid start

Newer rapid start ballast designs provide lament powerwindings within the ballast; these rapidly and continu-ously warm the laments/cathodes using low-voltage AC.No inductive voltage spike is produced for starting, so thelamps must be mounted near a grounded (earthed) re-ector to allow the glow discharge to propagate throughthe tube and initiate the arc discharge. In some lamps agrounded starting aid strip is attached to the outside ofthe lamp glass.

A rapid-start iron (magnetic) ballast continually heats the cath-odes at the ends of the lamps. This ballast runs two F40T12lamps in series.

2.6.4 Quick-start

Quick-start ballasts use a small auto-transformer to heatthe laments when power is rst applied. When an arcstrikes, the lament heating power is reduced and the tubewill start within half a second. The auto-transformer iseither combined with the ballast or may be a separateunit. Tubes need to be mounted near an earthed metal

reector in order for them to strike. Quick-start ballastsare more common in commercial installations becauseof lower maintenance costs. A quick-start ballast elim-inates the need for a starter switch, a common source oflamp failures. Nonetheless, Quick-start ballasts are alsoused in domestic (residential) installations because of thedesirable feature that a Quick-start ballast light turns onnearly immediately after power is applied (when a switchis turned on). Quick-start ballasts are used only on 240V circuits and are designed for use with the older, lessecient T12 tubes.

2.6.5 Semi-resonant start

A 65 watt uorescent lamp starting on a semi-resonant start cir-cuit

A semi-resonant start circuit diagram

The semi-resonant start circuit was invented by ThornLighting for use with T12 uorescent tubes. This methoduses a double wound transformer and a capacitor. Withno arc current, the transformer and capacitor resonateat line frequency and generate about twice the supplyvoltage across the tube, and a small electrode heatingcurrent.[30] This tube voltage is too low to strike the arcwith cold electrodes, but as the electrodes heat up tothermionic emission temperature, the tube striking volt-age falls below that of the ringing voltage, and the arcstrikes. As the electrodes heat, the lamp slowly, over

2.6 Starting 11

three to ve seconds, reaches full brightness. As the arccurrent increases and tube voltage drops, the circuit pro-vides current limiting.Semi-resonant start circuits are mainly restricted to usein commercial installations because of the higher initialcost of circuit components. However, there are no starterswitches to be replaced and cathode damage is reducedduring starting making lamps last longer, reducing main-tenance costs. Due to the high open circuit tube voltage,this starting method is particularly good for starting tubesin cold locations. Additionally, the circuit power factoris almost 1.0, and no additional power factor correctionis needed in the lighting installation. As the design re-quires that twice the supply voltage must be lower thanthe cold-cathode striking voltage (or the tubes would er-roneously instant-start), this design cannot be used with240 volt AC power unless the tubes are at least 1.5 meterlength. Semi-resonant start xtures are generally incom-patible with energy saving T8 retrot tubes, because suchtubes have a higher starting voltage than T12 lamps andmay not start reliably, especially in low temperatures. Re-cent proposals in some countries to phase out T12 tubeswill reduce the application of this starting method.

2.6.6 Programmed start

This is used with electronic ballasts shown below. Aprogrammed-start ballast is a more advanced version ofrapid start. This ballast applies power to the lamentsrst, then after a short delay to allow the cathodes to pre-heat, applies voltage to the lamps to strike an arc. Thisballast gives the best life and most starts from lamps, andso is preferred for applications with very frequent powercycling such as vision examination rooms and restroomswith a motion detector switch.

2.6.7 Electronic ballasts

Electronic ballast for uorescent lamp, 2x58W

Electronic ballasts employ transistors to change the sup-ply frequency into high-frequency AC while also regulat-ing the current ow in the lamp. Some still use an in-ductance to limit the current, but the higher frequencyallows a much smaller inductance to be used. Othersuse a capacitor-transistor combination to replace the in-ductor, since a transistor and capacitor working togethercan simulate the action of an inductor. These ballasts

Electronic ballast basic schematic

Fluorescent lamp with an electronic ballast.

Electronic ballasts and dierent compact uorescent lamps

take advantage of the higher eciency of lamps operatedwith higher-frequency current, which rises by almost 10%at 10 kHz, compared to eciency at normal power fre-quency. When the AC period is shorter than the relax-ation time to de-ionize mercury atoms in the dischargecolumn, the discharge stays closer to optimum operatingcondition.[31] Electronic ballasts typically work in rapidstart or instant start mode. Electronic ballasts are com-monly supplied with AC power, which is internally con-verted to DC and then back to a variable frequency ACwaveform. Depending upon the capacitance and the qual-ity of constant-current pulse-width modulation, this canlargely eliminate modulation at 100 or 120 Hz.Low cost ballasts mostly contain only a simple oscillatorand series resonant LC circuit. When turned on, the os-cillator starts, and resonant current causes on the LC cir-cuit. And this resonant current directly drive the switch-ing transistor through the ring core transformer. Thisprinciple is called the current resonant inverter circuit.After a short time the voltage across the lamp reaches

12 2 PRINCIPLES OF OPERATION

about 1 kV and the lamp ignites. The process is too fastto preheat the cathodes, so the lamp instant-starts in coldcathode mode. The cathode laments are still used forprotection of the ballast from overheating if the lampdoes not ignite. A few manufacturers use positive tem-perature coecient (PTC) thermistors to disable instantstarting and give some time to preheat the laments.More complex electronic ballasts use programmed start.The output frequency is started above the resonance fre-quency of the output circuit of the ballast; and after thelaments are heated, the frequency is rapidly decreased.If the frequency approaches the resonant frequency of theballast, the output voltage will increase so much that thelamp will ignite. If the lamp does not ignite, an electroniccircuit stops the operation of the ballast.Many electronic ballasts are controlled by amicrocontroller or similar, and these are sometimescalled digital ballasts. Digital ballasts can apply quitecomplex logic to lamp starting and operation. Thisenables functions such as testing for broken electrodesand missing tubes before attempting to start, auto detecttube replacement, and auto detection of tube type, suchthat a single ballast can be used with several dierenttubes, even those that operate at dierent arc currents,etc. Once such ne grained control over the starting andarc current is achievable, features such as dimming, andhaving the ballast maintain a constant light level againstchanging sunlight contribution are all easily includedin the embedded microcontroller software, and can befound in various manufacturers products.Since introduction in the 1990s, high-frequency ballastshave been used in general lighting xtures with eitherrapid start or pre-heat lamps. These ballasts convertthe incoming power to an output frequency in excessof 20 kHz. This increases lamp eciency. These areused in several applications, including new generationtanning lamp systems, whereby a 100 watt lamp (e.g.,F71T12BP) can be lit using 90 watts of actual powerwhile obtaining the same luminous ux (measured in lu-mens) asmagnetic ballasts.[32] These ballasts operate withvoltages that can be almost 600 volts, requiring some con-sideration in housing design, and can cause a minor lim-itation in the length of the wire leads from the ballast tothe lamp ends.

2.7 End of life

The end of life failure mode for uorescent lamps variesdepending on how they are used and their control geartype. Often the light will turn pink (see Loss of mercury)with black burns on the ends of the lamp due to sputteringof emission mix (see below). The lamp may also ickerat a noticeable rate (see Flicker problems). More infor-mation about normal failure modes are as follows:

2.7.1 Emission mix

Closeup of the lament on a low pressure mercury gas dischargelamp showing white thermionic emission mix coating on the cen-tral portion of the coil acting as hot cathode. Typically made ofa mixture of barium, strontium and calcium oxides, the coatingis sputtered away through normal use, often eventually resultingin lamp failure.

The "emission mix" on the lamp laments/cathodes isrequired to enable electrons to pass into the gas viathermionic emission at the lamp operating voltages used.The mix is slowly sputtered o by bombardment withelectrons and mercury ions during operation, but a largeramount is sputtered o each time the lamp is started withcold cathodes. The method of starting the lamp has asignicant impact on this. Lamps operated for typicallyless than 3 hours each switch-on will normally run outof the emission mix before other parts of the lamp fail.The sputtered emission mix forms the dark marks at thelamp ends seen in old lamps. When all the emission mixis gone, the cathode cannot pass sucient electrons intothe gas ll to maintain the gas discharge at the designedlamp operating voltage. Ideally, the control gear shouldshut down the lamp when this happens. However, due tocost, negative dierential resistance and sometimes highstarting voltage, some control gear will provide sucientincreased operating voltage to continue lighting the lampin cold cathode mode. This will cause overheating of thelamp end and rapid disintegration of the electrodes (la-ment goes open-circuit) and lament support wires untilthey are completely gone or the glass cracks, wreckingthe low pressure gas ll and stopping the gas discharge.

2.7.2 Ballast electronics

This may occur in compact uorescent lamps with inte-gral electrical ballasts or in linear lamps. Ballast electron-ics failure is a somewhat random process that follows thestandard failure prole for any electronic device. There is

13

an initial small peak of early failures, followed by a dropand steady increase over lamp life. Life of electronics isheavily dependent on operating temperatureit typicallyhalves for each 10 C temperature rise. The quoted av-erage life of a lamp is usually at 25 C (77 F) ambient(this may vary by country). The average life of the elec-tronics at this temperature is normally greater than this,so at this temperature, not many lamps will fail due tofailure of the electronics. In some ttings, the ambienttemperature could be well above this, in which case fail-ure of the electronics may become the predominant fail-ure mechanism. Similarly, running a compact uorescentlamp base-up will result in hotter electronics, which cancause shorter average life (particularly with higher powerrated ones). Electronic ballasts should be designed to shutdown the tube when the emission mix runs out as de-scribed above. In the case of integral electronic ballasts,since they never have to work again, this is sometimesdone by having them deliberately burn out some compo-nent to permanently cease operation.In most CFLs the laments are connected in series, with asmall capacitor between them. The discharge, once lit, isin parallel to the capacitor and presents a lower-resistancepath, eectively shorting the capacitor out.

2.7.3 Phosphor

The phosphor drops o in eciency during use. Byaround 25,000 operating hours, it will typically be halfthe brightness of a new lamp (although some manufactur-ers claim much longer half-lives for their lamps). Lampsthat do not suer failures of the emission mix or inte-gral ballast electronics will eventually develop this failuremode. They still work, but have become dim and inef-cient. The process is slow, and often becomes obviousonly when a new lamp is operating next to an old one.

2.7.4 Loss of mercury

As in all mercury-based gas-lled tubes, mercury isslowly adsorbed into the glass, phosphor, and tube elec-trodes throughout the life of the lamp, until it can nolonger function. Newer lamps have just enough mercuryto last the expected life of the lamp. Loss of mercury willtake over from failure of the phosphor in some lamps.The failure symptoms are similar, except loss of mercuryinitially causes an extended run-up time to full light out-put, and nally causes the lamp to glow a dim pink whenthe mercury runs out and the argon base gas takes over asthe primary discharge.[33]

Subjecting the tube to asymmetric waveforms, where thetotal current ow through the tube does not cancel outand the tube eectively operates under a DC bias, causesasymmetric distribution of mercury ions along the tubedue to cataphoresis. The localized depletion of mercuryvapor pressure manifests as pink luminescence of the

base gas in the vicinity of one of the electrodes, and theoperating lifetime of the lamp may be dramatically short-ened. This can be an issue with some poorly designedinverters.[34]

2.7.5 Burned laments

The laments can burn at the end of the lamps lifetime,opening the circuit and losing the capability to heat up.Both laments lose function as they are connected in se-ries, with just a simple switch start circuit a broken la-ment will render the lamp completely useless. Filamentsrarely burn or fail open circuit unless the lament be-comes depleted of emitter and the control gear is able tosupply a high enough voltage across the tube to operate itin cold cathode mode. Some digital electronic ballasts arecapable of detecting broken laments and can still strikean arc with one or both laments broken providing thereis still sucient emitter. A broken lament in a lamp at-tached to a magnetic ballast often causes both lamps toburn out or icker.

3 Phosphors and the spectrum ofemitted light

Light from a uorescent tube lamp reected by a CD shows theindividual bands of color.

The spectrum of light emitted from a uorescent lampis the combination of light directly emitted by the mer-cury vapor, and light emitted by the phosphorescent coat-ing. The spectral lines from the mercury emission andthe phosphorescence eect give a combined spectral dis-tribution of light that is dierent from those producedby incandescent sources. The relative intensity of lightemitted in each narrow band of wavelengths over the vis-ible spectrum is in dierent proportions compared to thatof an incandescent source. Colored objects are perceiveddierently under light sources with diering spectral dis-tributions. For example, some people nd the color ren-dition produced by some uorescent lamps to be harshand displeasing. A healthy person can sometimes appearto have an unhealthy skin tone under uorescent lighting.

14 3 PHOSPHORS AND THE SPECTRUM OF EMITTED LIGHT

The extent to which this phenomenon occurs is related tothe lights spectral composition, and may be gauged by itscolor rendering index (CRI).

3.1 Color temperature

Main article: Color temperatureCorrelated color temperature (CCT) is a measure of the

1500K 8000K

2200K

2700K

3000K

3200K

4000K

4200K

5500K

Kelvin Temperature

ChartHigh

Press

ure So

dium

Stand

ard In

cande

scent

Halog

enWh

ite Me

tal Ha

lide

Daylig

ht Me

tal Ha

lide

Stand

ard Cl

ear M

etal H

alide

Cool W

ite Flu

oresce

nt

The color temperature of dierent electric lamps

shade of whiteness of a light source compared witha blackbody. Typical incandescent lighting is 2700 K,which is yellowish-white. Halogen lighting is 3000 K.Fluorescent lamps are manufactured to a chosen CCT byaltering the mixture of phosphors inside the tube. Warm-white uorescents have CCT of 2700 K and are popularfor residential lighting. Neutral-white uorescents have aCCT of 3000 K or 3500 K. Cool-white uorescents havea CCT of 4100 K and are popular for oce lighting. Day-light uorescents have a CCT of 5000K to 6500K, whichis bluish-white.High CCT lighting generally requires higher light lev-els. At dimmer illumination levels, the human eye per-ceives lower color temperatures as more pleasant, as re-lated through the Kruithof curve. So, a dim 2700 K in-candescent lamp appears comfortable and a bright 5000K lamp also appears natural, but a dim 5000 K uores-cent lamp appears too pale. Daylight-type uorescentslook natural only if they are very bright.

3.2 Color rendering index

Main article: Color rendering index

Color rendering index (CRI) is a measure of how wellcolors can be perceived using light from a source, rela-tive to light from a reference source such as daylight or ablackbody of the same color temperature. By denition,an incandescent lamp has a CRI of 100. Real-life u-orescent tubes achieve CRIs of anywhere from 50 to 99.Fluorescent lamps with lowCRI have phosphors that emittoo little red light. Skin appears less pink, and hence un-healthy compared with incandescent lighting. Coloredobjects appear muted. For example, a low CRI 6800 Khalophosphate tube (an extreme example) will make redsappear dull red or even brown. Since the eye is relatively

A helical cool-white uorescent lamp reected in a diractiongrating reveals the various spectral lines which make up the light.

Fluorescent spectra in comparison with other forms of lighting.Clockwise from upper left: Fluorescent lamp, incandescent bulb,candle ame and LED lighting.

less ecient at detecting red light, an improvement incolor rendering index, with increased energy in the redpart of the spectrum, may reduce the overall luminousecacy.[35]

Lighting arrangements use uorescent tubes in an assort-ment of tints of white. Sometimes this is because of thelack of appreciation for the dierence or importance ofdiering tube types. Mixing tube types within ttings canimprove the color reproduction of lower quality tubes.

3.3 Phosphor composition

Some of the least pleasant light comes from tubes con-taining the older, halophosphate-type phosphors (chem-ical formula Ca5(PO4)3(F, Cl):Sb3+, Mn2+). This phos-phor mainly emits yellow and blue light, and relativelylittle green and red. In the absence of a reference, thismixture appears white to the eye, but the light has an in-complete spectrum. The CRI of such lamps is around 60.Since the 1990s, higher quality uorescent lamps use ei-ther a higher CRI halophosphate coating, or a triphos-

5.2 Life 15

phor mixture, based on europium and terbium ions, thathave emission bands more evenly distributed over thespectrum of visible light. High CRI halophosphate andtriphosphor tubes give a more natural color reproductionto the human eye. The CRI of such lamps is typically82100.

4 ApplicationsFluorescent lamps come in many shapes and sizes. Thecompact uorescent lamp (CFL) is becoming more pop-ular. Many compact uorescent lamps integrate the aux-iliary electronics into the base of the lamp, allowing themto t into a regular light bulb socket.In US residences, uorescent lamps are mostly found inkitchens, basements, or garages, but schools and busi-nesses nd the cost savings of uorescent lamps to be sig-nicant and rarely use incandescent lights. Tax incentivesand building codes result in higher use in places such asCalifornia.In other countries, residential use of uorescent lightingvaries depending on the price of energy, nancial and en-vironmental concerns of the local population, and accept-ability of the light output. In East and Southeast Asia it isvery rare to see incandescent bulbs in buildings anywhere.Some countries are encouraging the phase-out of incan-descent light bulbs and substitution of incandescent lampswith uorescent lamps or other types of energy-ecientlamps.In addition to general lighting, special uorescent lightsare often used in stage lighting for lm and video pro-duction. They are cooler than traditional halogen lightsources, and use high-frequency ballasts to prevent videoickering and high color-rendition index lamps to approx-imate daylight color temperatures.

5 Advantages

5.1 Luminous ecacy

Fluorescent lamps convert more of the input power tovisible light than incandescent lamps, though as of 2013LEDs are sometimes even more ecient and are morerapidly increasing in eciency. A typical 100 watt tung-sten lament incandescent lamp may convert only 5% ofits power input to visible white light (400700 nm wave-length), whereas typical uorescent lamps convert about22% of the power input to visible white light.[36]

The ecacy of uorescent tubes ranges from about 16lumens per watt for a 4 watt tube with an ordinary ballastto over 100 lumens per watt[37] with a modern electronicballast, commonly averaging 50 to 67 lm/Woverall. Mostcompact uorescents above 13 watts with integral elec-

tronic ballasts achieve about 60 lm/W. Lamps are ratedby lumens after 100 hours of operation.[38] For a givenuorescent tube, a high-frequency electronic ballast givesabout a 10% ecacy improvement over an inductive bal-last. It is necessary to include the ballast loss when eval-uating the ecacy of a uorescent lamp system; this canbe about 25% of the lamp power with magnetic ballasts,and around 10% with electronic ballasts.Fluorescent lamp ecacy is dependent on lamp temper-ature at the coldest part of the lamp. In T8 lamps this isin the center of the tube. In T5 lamps this is at the end ofthe tube with the text stamped on it. The ideal tempera-ture for a T8 lamp is 25 C (77 F) while the T5 lamp isideally at 35 C (95 F).

5.2 Life

Typically a uorescent lamp will last 10 to 20 times aslong as an equivalent incandescent lamp when operatedseveral hours at a time. Under standard test conditionsgeneral lighting lamps have 9,000 hours or longer servicelife.[39]

The higher initial cost of a uorescent lamp comparedwith an incandescent lamp is usually more than compen-sated for by lower energy consumption over its life.[40]

A fewmanufacturers are producing T8 lampswith 90,000hour lamp lives, rivalling the life of LED lamps.

5.3 Lower luminance

Compared with an incandescent lamp, a uorescent tubeis a more diuse and physically larger light source. Insuitably designed lamps, light can be more evenly dis-tributed without point source of glare such as seen froman undiused incandescent lament; the lamp is largecompared to the typical distance between lamp and il-luminated surfaces.

5.4 Lower heat

Fluorescent lamps give o about one-fth the heat ofequivalent incandescent lamps. This greatly reduces thesize, cost, and energy consumption devoted to air con-ditioning for oce buildings that would typically havemany lights and few windows.

6 Disadvantages

6.1 Frequent switching

If the lamp is installed where it is frequently switched onand o, it will age rapidly.[41] Under extreme conditions,

16 6 DISADVANTAGES

its lifespan may be much shorter than a cheap incandes-cent lamp. Each start cycle slightly erodes the electron-emitting surface of the cathodes; when all the emissionmaterial is gone, the lamp cannot start with the availableballast voltage. Fixtures intended for ashing of lights(such as for advertising) will use a ballast that maintainscathode temperature when the arc is o, preserving thelife of the lamp.The extra energy used to start a uorescent lamp is equiv-alent to a few seconds of normal operation; it is moreenergy-ecient to switch o lamps when not required forseveral minutes.[42][43]

6.2 Health and safety issues

Main article: Fluorescent lamps and health

If a uorescent lamp is broken, a very small amount ofmercury can contaminate the surrounding environment.About 99% of the mercury is typically contained in thephosphor, especially on lamps that are near the end oftheir life.[44] The broken glass is usually considered agreater hazard than the small amount of spilled mercury.The EPA recommends airing out the location of a uores-cent tube break and using wet paper towels to help pickup the broken glass and ne particles. Any glass and usedtowels should be disposed of in a sealed plastic bag. Vac-uum cleaners can cause the particles to become airborne,and should not be used.[45]

Fluorescent lamps with magnetic ballasts icker at a nor-mally unnoticeable frequency of 100 or 120 Hz and thisickering can cause problems for some individuals withlight sensitivity;[46] they are listed as problematic for someindividuals with autism, epilepsy,[47] lupus,[48] chronic fa-tigue syndrome, Lyme disease,[49] and vertigo.[50] Neweruorescent lights without magnetic ballasts have essen-tially eliminated icker.[51]

6.3 Ultraviolet emission

Fluorescent lamps emit a small amount of ultraviolet(UV) light. A 1993 study in the US found that ultravio-let exposure from sitting under uorescent lights for eighthours is equivalent to only oneminute of sun exposure.[52]Very sensitive individuals may experience a variety ofhealth problems relating to light sensitivity that is aggra-vated by articial lighting.The ultraviolet light from a uorescent lamp can de-grade the pigments in paintings (especially watercolorpigments) and bleach the dyes used in textiles and someprinting. Valuable art work must be protected from ul-traviolet light by placing additional glass or transparentacrylic sheets between the lamp and the art work.

6.4 Ballast

Magnetic single-lamp ballasts have a low power factor.

Fluorescent lamps require a ballast to stabilize the currentthrough the lamp, and to provide the initial striking volt-age required to start the arc discharge. This increases thecost of uorescent light xtures, though often one ballastis shared between two or more lamps. Electromagneticballasts with a minor fault can produce an audible hum-ming or buzzing noise. Magnetic ballasts are usually lledwith a tar-like potting compound to reduce emitted noise.Hum is eliminated in lamps with a high-frequency elec-tronic ballast. Energy lost inmagnetic ballasts was around10% of lamp input power according to GE literature from1978.[21] Electronic ballasts reduce this loss.

6.5 Power quality and radio interference

Simple inductive uorescent lamp ballasts have a powerfactor of less than unity. Inductive ballasts include powerfactor correction capacitors. Simple electronic ballastsmay also have low power factor due to their rectier in-put stage.Fluorescent lamps are a non-linear load and generateharmonic currents in the electrical power supply. Thearc within the lamp may generate radio frequency noise,which can be conducted through power wiring. Suppres-sion of radio interference is possible. Very good suppres-sion is possible, but adds to the cost of the uorescentxtures.

6.6 Operating temperature

Fluorescent lamps operate best around room temper-ature. At much lower or higher temperatures, e-ciency decreases. At below-freezing temperatures stan-dard lamps may not start. Special lamps may be neededfor reliable service outdoors in cold weather. In appli-cations such as road and railway signalling, uorescentlamps which do not generate as much heat as incandes-

6.8 Flicker problems 17

cent lamps may not melt snow and ice build up aroundthe lamp, leading to reduced visibility.

6.7 Lamp shape

Fluorescent tubes are long, low-luminance sources com-pared with high pressure arc lamps, incandescent lampsand LEDs. However, low luminous intensity of the emit-ting surface is useful because it reduces glare. Lamp x-ture design must control light from a long tube instead ofa compact globe.The compact uorescent lamp (CFL) replaces regularincandescent bulbs. However, some CFLs will not tsome lamps, because the harp (heavy wire shade supportbracket) is shaped for the narrow neck of an incandescentlamp, while CFLs tend to have a wide housing for theirelectronic ballast close to the lamps base.

6.8 Flicker problems

The beat eect problem created when shooting photos understandard uorescent lighting

Fluorescent lamps using a magnetic power line frequencyballast do not give out a steady light; instead, they ickerat twice the supply frequency. This results in uctua-tions not only with light output but color temperature aswell,[53] which may pose problems for photography andpeople who are sensitive to the icker. Even among per-sons not sensitive to light icker, a stroboscopic eectcan be noticed, where something spinning at just the rightspeedmay appear stationary if illuminated solely by a sin-gle uorescent lamp. This eect is eliminated by pairedlamps operating on a lead-lag ballast. Unlike a true strobelamp, the light level drops in appreciable time and so sub-stantial blurring of the moving part would be evident.In some circumstances, uorescent lamps operated at thepower supply frequency (50 or 60 Hz) can also produceicker at the same frequency itself, which is noticeableby more people. This can happen in the last few hoursof tube life when the cathode emission coating at one end

has almost run out, and that cathode starts having di-culty emitting enough electrons into the gas ll, result-ing in slight rectication and hence uneven light output inpositive and negative going AC cycles. Power frequencyicker can also sometimes be emitted from the very endsof the tubes, if each tube electrode produces a slightlydierent light output pattern on each half-cycle. Flickerat power frequency is more noticeable in the peripheralvision than it is when viewed directly, as is all icker(since the peripheral vision is fasterhas a higher crit-ical frequencythan the central vision).Near the end of life, uorescent lamps can start icker-ing at a frequency lower than the power frequency. Thisis due to a dynamic instability inherent in the negativeresistance of the plasma source,[54] which can be from abad lamp, a bad ballast, or a bad starter; or occasionallyfrom a poor connection to power.

The beat eect problem created when shooting lms understandard uorescent lighting

New uorescent lamps may show a twisting spiral patternof light in a part of the lamp. This eect is due to loosecathode material and usually disappears after a few hoursof operation.[55]

Electromagnetic ballasts may also cause problems forvideo recording as there can be a beat eect betweenthe periodic reading of a cameras sensor and the uctu-ations in intensity of the uorescent lamp.Fluorescent lamps using high-frequency electronic bal-lasts do not produce visible light icker, since aboveabout 5 kHz, the excited electron state half-life is longerthan a half cycle, and light production becomes continu-ous. Operating frequencies of electronic ballasts are se-lected to avoid interference with infrared remote controls.Poor quality (or failing) electronic ballasts may have in-sucient reservoir capacitance or have poor regulation,thereby producing considerable 100/120 Hz modulationof the light.

18 8 OTHER FLUORESCENT LAMPS

6.9 DimmingFluorescent light xtures cannot be connected to dimmerswitches intended for incandescent lamps. Two eectsare responsible for this: the waveform of the voltage emit-ted by a standard phase-control dimmer interacts badlywith many ballasts, and it becomes dicult to sustainan arc in the uorescent tube at low power levels. Dim-ming installations require a compatible dimming ballast.These systems keep the cathodes of the uorescent tubefully heated even as the arc current is reduced, promotingeasy thermionic emission of electrons into the arc stream.CFLs are available that work in conjunction with a suit-able dimmer.

6.10 Disposal and recyclingMain article: Fluorescent lamp recycling

The disposal of phosphor and particularly the toxicmercury in the tubes is an environmental issue. Govern-mental regulations in many areas require special disposalof uorescent lamps separate from general and householdwastes. For large commercial or industrial users of uo-rescent lights, recycling services are available in many na-tions, and may be required by regulation.[56][57] In someareas, recycling is also available to consumers.[58]

7 Lamp sizes and designationsMain article: Fluorescent lamp formats

Systematic nomenclature identies mass-market lamps asto general shape, power rating, length, color, and otherelectrical and illuminating characteristics.

8 Other uorescent lampsBlack lights Blacklights are a subset of uorescent

lamps that are used to provide near ultraviolet light(at about 360 nm wavelength). They are built in thesame fashion as conventional uorescent lamps butthe glass tube is coated with a phosphor that convertsthe short-wave UV within the tube to long-wave UVrather than to visible light. They are used to pro-voke uorescence (to provide dramatic eects us-ing blacklight paint and to detect materials such asurine and certain dyes that would be invisible in vis-ible light) as well as to attract insects to bug zappers.

So-called blacklite blue lamps are also made from moreexpensive deep purple glass known as Woods glassrather than clear glass. The deep purple glass l-ters out most of the visible colors of light directly

emitted by the mercury-vapor discharge, producingproportionally less visible light compared with UVlight. This allows UV-induced uorescence to beseenmore easily (thereby allowing blacklight postersto seemmuchmore dramatic). The blacklight lampsused in bug zappers do not require this renement soit is usually omitted in the interest of cost; they arecalled simply blacklite (and not blacklite blue).

Tanning lamps The lamps used in tanning beds con-tain a dierent phosphor blend (typically 3 to 5 ormore phosphors) that emits both UVA and UVB,provoking a tanning response in most human skin.Typically, the output is rated as 3% to 10% UVB(5% most typical) with the remaining UV as UVA.These are mainly F71, F72 or F73 HO (100 W)lamps, although 160 W VHO are somewhat com-mon. One common phosphor used in these lampsis lead-activated barium disilicate, but a europium-activated strontium uoroborate is also used. Earlylamps used thallium as an activator, but emissionsof thallium during manufacture were toxic.[59]

UVB Medical lamps The lamps used in Phototherapycontain a phosphor that emits only UVB Ultravio-let light. There are two types: Broadband UVB thatgives 290-320 nanometer with peak wavelength of306nm, and Narrowband UVB that gives 311-313nanometer. Due to its longer wavelength the Nar-rowband UVB requires a 10 times higher dose to theskin, compared to the broadband. The Narrowbandis good for Psoriasis, Eczema (Atopic Dermatitis).Vitiligo, Lichen Planus and some other skin dis-eases. The Broadband is better for increasing Vi-tamin D3 in the body.

Grow lamps Grow lamps contain phosphor blends thatencourage photosynthesis, growth, or owering inplants, algae, photosynthetic bacteria, and otherlight-dependent organisms. These often emit lightin the red and blue color range, which is absorbed bychlorophyll and used for photosynthesis in plants.[60]

Infrared lamps Lamps can be made with a lithiummetaluminate phosphor activated with iron. Thisphosphor has peak emissions between 675 and 875nanometers, with lesser emissions in the deep redpart of the visible spectrum.[61]

Bilirubin lamps Deep blue light generated from aeuropium-activated phosphor is used in the lighttherapy treatment of jaundice; light of this colorpenetrates skin and helps in the breakup of excessbilirubin.[19]

Germicidal lamps Germicidal lamps depend on theproperty that spectrum of 254 nm kills most germs.Germicidal lamps contain no phosphor at all (mak-ing them mercury vapor gas discharge lamps ratherthan uorescent) and their tubes are made of fused

19

quartz that is transparent to the UV light emitted bythe mercury discharge. The 254 nm UV emittedby these tubes will kill germs and ionize oxygen toozone. In addition it can cause eye and skin damageand should not be used or observed without eye andskin protection. Besides their uses to kill germs andcreate ozone, they are sometimes used by geologiststo identify certain species of minerals by the color oftheir uorescence. When used in this fashion, theyare tted with lters in the same way as blacklight-blue lamps are; the lter passes the short-wave UVand blocks the visible light produced by the mer-cury discharge. They are also used in some EPROMerasers.

Germicidal lamps have designations beginning with G(meaning 'Germicidal'), rather than F, for exampleG30T8 for a 30-watt, 1-inch (2.5 cm) diameter, 36-inch (91 cm) long germicidal lamp (as opposed toan F30T8, which would be the uorescent lamp ofthe same size and rating).

Electrodeless lamps Electrodeless induction lamps areuorescent lamps without internal electrodes. Theyhave been commercially available since 1990. Acurrent is induced into the gas column usingelectromagnetic induction. Because the electrodesare usually the life-limiting element of uorescentlamps, such electrodeless lamps can have a very longservice life, although they also have a higher pur-chase price.

Cold-cathode uorescent lamps (CCFL) Cold-cathode uorescent lamps are used as backlightingfor LCD displays in personal computer and TVmonitors. They are also popular with computercase modders in recent years.

9 Science demonstrations

Fluorescent lamps can be illuminated by means otherthan a proper electrical connection. These other methods,however, result in very dim or very short-lived illumina-tion, and so are seen mostly in science demonstrations.Static electricity or a Van de Graa generator will causea lamp to ash momentarily as it discharges a high volt-age capacitance. A Tesla coil will pass high-frequencycurrent through the tube, and since it has a high voltageas well, the gases within the tube will ionize and emitlight. Capacitive coupling with high-voltage power linescan light a lamp continuously at low intensity, dependingon the intensity of the electrostatic eld.Also, placing a uorescent lamp half way up a two-wayradio antenna while transmitting will illuminate the lampdue to the RF energy.

Capacitive coupling with high-voltage power lines can light alamp continuously at low intensity.

10 See also Compact uorescent lamp Fluorescent lamp formats Fluorescent lamp recycling Fluorescent lamps and health Metal halide lamp List of light sources Gas lled tube

11 References[1] HTTP 404 Error Message - WA State Dept. of Ecology

[2] M. A. Laughton Electrical Engineers Reference Book Six-teenth Edition, Newnes, 2003 ISBN 0-7506-4637-3, page21-12

[3] Mercury-Containing Light Bulb (Lamp) Recycling | Uni-versal Waste | US EPA

[4] Gribben, John; The Scientists; A History of Science ToldThrough the Lives of Its Greatest Inventors"; RandomHouse; 2004; pp 424432; ISBN 978-0-8129-6788-3

[5] See Bright 1949, pp. 381385 for discussion of early his-tory

[6] US 865367 Fluorescent Electric Lamp

20 11 REFERENCES

[7] Mr. Moores Etheric Light. The Young Newark Electri-cians New And Successful Device.. New York Times.October 2, 1896. Retrieved 2008-05-26. Paid access.

[8] Gaster, Leon; Dow, John Stewart (1915). Modern illumi-nants and illuminating engineering. Whittaker & Co. pp.107111.

[9] Bright, Arthur A., Jr. (1949). The Electric-Lamp Indus-try. MacMillan. Pages 221223 describe Moore tubes.Pages 369374 describe neon tube lighting. Page 385 dis-cusses Rislers contributions to uorescent coatings in the1920s. Pages 388391 discuss the development of thecommercial uorescent at General Electric in the 1930s.

[10] Weeks, Mary Elvira (2003). Discovery of the Elements:Third Edition (reprint). Kessinger Publishing. p. 287.ISBN 978-0-7661-3872-8.

[11] Claude, Georges (November 1913). The Developmentof Neon Tubes. The Engineering Magazine: 271274.

[12] van Dulken, Stephen (2002). Inventing the 20th century:100 inventions that shaped the world : from the airplaneto the zipper. New York University Press. p. 42. ISBN978-0-8147-8812-7.

[13] US patent 1790153, Albert W. Hull, Electrical Dis-charge Device and Method of Operation, issued 1931-01-27, assigned to General Electric Company

[14] US patent 2182732, Friedrich Meyer; Hans-JoachimSpanner&EdmundGermer, Metal Vapor Lamp, issued1939-12-05, assigned to General Electric Company

[15] Lighting A Revolution: 20th Century Store-room

[16] Kane, Raymond; Sell, Heinz (2001). A Review of EarlyInorganic Phosphors. Revolution in lamps: a chronicle of50 years of progress. p. 98. ISBN 978-0-88173-378-5.

[17] William M. Yen, Shigeo Shionoya, Hajime Yamamoto,Practical Applications of Phosphors,CRC Press, 2006,ISBN 1-4200-4369-2, pages 84-85

[18] Kulshreshtha, Alok K. (2009). Basic Electrical Engineer-ing: Principles and Applications. India: Tata McGraw-Hill Education. p. 801. ISBN 0-07-014100-2. The par-tial pressure of the mercury vapor alone is about 0.8 Pa(8 millionths of atmospheric pressure), in a T12 40-wattlamp. See Kane and Sell, 2001, page 185

[19] Van Broekhoven, Jacob (2001). Chapter 5: Lamp Phos-phors. In Kane, Raymond; Sell, Heinz. Revolution inlamps: a chronicle of 50 years of progress (2nd ed.). TheFairmont Press, Inc. p. 93. ISBN 0-88173-378-4.

[20] T12 species the bulbs diameter in 1/8 inch units; a T12bulb is 12(1/8) inches or 1.5 in (38 mm) in diameter.

[21] General Electric, Fluorescent Lamps Technical Bulletin TP111R, December 1978 pages 1011

[22] page 188

[23] pages 196197

[24] Philips Semiconductor: Power Semiconductor Applica-tions - Lighting, p579

[25] Datasheet of typical electronic starter (not fast start), withdetailed explanation of operation

[26] Datasheet of typical fast start electronic starter, with de-tailed explanation of operation

[27] Data on an ultrafast starter, with nominal startup time of0.3 seconds

[28] Data on a typical starter for even adverse conditions, withnominal startup time of 2.4 seconds

[29] Quick Start for Fluorescent Lights All three of the 'FAST'(< .5 seconds) starter brands caused an audible 'BUR-RRRRRRP' noise in some light ttings as they started andthis is an inherent problem caused by their use of the faster'DC' heating. It is worse with higher wattage tubes and ifthere is any loose metal in the light tting.

[30] Thorn Lighting Technical Handbook

[31] page 182

[32] Energy Conservation Standards for Fluorescent LampBallasts (PDF). US Department of Energy. p. 31. Re-trieved 29 January 2012.

[33]

[34] http://www.htl.co.jp/img/p_pro4_p10.pdf

[35] page 8

[36] page 20

[37] Panasonic. Panasonic Spiral Fluorescent ceiling lights,124.3lm/W. Retrieved 2010-09-27.

[38] Klipstein, Donald L. Light and Lighting Facts and Bitsof Data!". Retrieved 2007-12-29.

[39] Fink, Donald G.; Beaty, H.Wayne, eds. (1978). StandardHandbook for Electrical Engineers (11th ed.). McGrawHill. pp. 2217. ISBN 978-0-070-20974-9.

[40] National Research Council (U.S.). Building Research In-stitute. Building illumination: the eect of new lightinglevels Publisher National Academies, 1959. Page 81

[41] Compact Fluorescent Lighting (PDF). eere.energy.gov.Archived from the original (PDF) on May 11, 2011. Re-trieved 24 July 2012.

[42] Science Fact or Science Fiction: Fluorescent Lights.Quirks and Quarks (CBC). Archived from the original onOctober 28, 2011. Retrieved 27 October 2011.

[43] When to Turn O Your Lights. U.S. Department of En-ergy. U.S. Department of Energy. Retrieved 28 Novem-ber 2012.

[44] Floyd, et al. (2002), quoted on page 184 of Toolkitfor identication and quantication of mercury releases(PDF)

[45] Fluorescent lamp cleanup Accessed 22 Apr 2009.

[46] Working with Light Sensitivity.

[47] Accommodation Ideas for Employees with Epilepsy.

21

[48] Accommodation and Compliance Series: Employeeswith Lupus.

[49] Shadick NA, Phillips CB, Sangha O et al. (December1999). Musculoskeletal and neurologic outcomes in pa-tients with previously treated Lyme disease. Ann. Intern.Med. 131 (12): 91926. doi:10.7326/0003-4819-131-12-199912210-00003. PMID 10610642.

[50] Accommodating People with Vertigo.

[51] Lighting icker, retrieved 2010 April 19

[52] Lytle, CD; Cyr, WH; Beer, JZ; Miller, SA; James, RH;Landry, RJ; Jacobs, ME; Kaczmarek, RG; Sharkness,CM; Gaylor, D et al. (December 1993). An Estimationof Squamous Cell Carcinoma Risk from Ultraviolet Ra-diation Emitted by Fluorescent Lamps. PhotodermatolPhotoimmunol Photomed 9 (6): 26874. PMID 1343229.

[53] Exposure and Color Temperature Variations When Pho-tographing Under Fluorescent Lights

[54] Glozman, Stanislav; Ben-Yaakov, Shmuel (SeptemberOctober 2001). Dynamic Interaction Analysis of HFBallasts and Fluorescent Lamps Based on Envelope Sim-ulation. IEEE Transactions on Industry Applications 37(5): 15311536. doi:10.1109/28.952531.

[55] page 22

[56] LampRecycle.org Commercial Lighting: Lamp Recyclers

[57] EPA.gov Mercury-Containing Light Bulb (Lamp) Regu-latory Framework

[58] EPA.gov Mercury-Containing Light Bulb (Lamp) Collec-tion and Recycling Programs Where You Live

[59] page 120

[60] Goins, GD and Yorio, NC and Sanwo, MM and Brown,CS (1997). Photomorphogenesis, photosynthesis, andseed yield of wheat plants grown under red light-emittingdiodes (LEDs) with and without supplemental blue light-ing. Journal of Experimental Botany (Soc ExperimentBiol) 48 (7): 14071413. doi:10.1093/jxb/48.7.1407.

[61] pg. 122

12 Further reading Bright, Arthur Aaron (1949). The Electric-Lamp In-dustry: Technological Change and Economic Devel-opment from 1800 to 1947. Macmillan Co.

Emanuel Gluskin, The uorescent lamp circuit,(Circuits & Systems Expositions)

IEEE Transactions on Circuits and Systems, Part I:Fundamental Theory and Applications 46(5), 1999(529-544).

13 External links Popular Science, January 1940 Fluorescent Lamps T5 Fluorescent Systems Lighting Research Cen-ter Research about the improved T5 relative to theprevious T8 standard

NASA: The Fluorescent Lamp: A plasma you canuse

How Fluorescent Tubes are Manufactured onYouTube

Museum of Electric Lamp Technology R. N. Thayer (1991-10-25). The FluorescentLamp: Early U. S. Development. The Report cour-tesy of General Electric Company. Retrieved 2007-03-18.

Wiebe E. Bijker,Of bicycles, bakelites, and bulbs: to-ward a theory of sociotechnical change MIT Press,1995, Chapter 4, preview available at Google Books,on the social construction of uorescent lighting

Explanations and schematics of some uorescentlamps

Consumer Guide to Fluorescent Light Bulbs pro-vided by Superior Lighting

22 14 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

14 Text and image sources, contributors, and licenses14.1 Text

Fluorescent lamp Source: http://en.wikipedia.org/wiki/Fluorescent_lamp?oldid=666190291 Contributors: AxelBoldt, Bryan Derksen,Malcolm Farmer, Rjstott, Lorax, Codeczero, Ray Van De Walker, Heron, Hephaestos, Frecklefoot, Edward, RTC, Delirium, Kosebamse,Ahoerstemeier, Ronz, Kragen, Glenn, Andres, Glueball, Smack, Tobyvoss, Mulad, Ec5618, Bemoeial, Reddi, Stone, Radiojon, Laussy,Maximus Rex, Taxman, Omegatron, David.Monniaux, Jeq, Donarreiskoer, Robbot, Ke4roh, Hankwang, Chealer, Chris 73, RedWolf,Academic Challenger, Sndrsn, Bkell, EvilPettingZoo, Jpo, Gwalla, DocWatson42, MPF, DavidCary, Art Carlson, Brona, Archenzo, Bob-blewik, Edcolins, Neilc, Vadmium, Chowbok, Gadum, Andycjp, Dan aka jack, H Padleckas, Icairns, Blue387, Iantresman,WpZurp, KevinRector, Deglr6328, Inkwina, Qui1che, Mormegil, JTN, Discospinster, Shinglor, YUL89YYZ, Bender235, Jaberwocky6669, Kbh3rd,Mattdm, Mcpusc, MBisanz, Wsher, Evand, Dennis Brown, The Noodle Incident, West London Dweller, Bobo192, Snozzberry, Meg-gar, BrokenSegue, Rmv, Ygfperson, Joe Jarvis, Jhd, WideArc, Alansohn, Mgaved, Guy Harris, Atlant, Keenan Pepper, Andrew Gray,Sade, Nasukaren, Stevestrange, Stillnotelf, Miltonhowe, Wtshymanski, Shoey, Vuo, H2g2bob, Skatebiker, Gene Nygaard, Cnsupplier,Kbolino, Kenyon, Shimeru, JimJim, Linas, Mindmatrix, Jpers36, Davidkazuhiro, Pol098, Slike2, Cbdorsett, Isnow, SDC, Zzyzx11, Crucis,Marudubshinki, BD2412, Reisio, Saperaud~enwiki, Rjwilmsi, Hitssquad, Hezery99, Mzhao, SMC, Snsh, Vegaswikian, Krash, Fred Brad-stadt, GregAsche, Splarka, G Clark, UltraMako101, SiriusB, Nihiltres, Who, Gurch, A. Square, Lmatt, Srleer, Milomedes, Bgwhite,Adoniscik, YurikBot, Ugha, Wavelength, Jamesmorrison, Huw Powell, H005, Midgley, RussBot, DMahalko, Hellbus, Gaius Cornelius,Shaddack, Rsrikanth05, Anomalocaris, David R. Ingham, Bvanderveen, Grafen, Gerben49~enwiki, CaliforniaAliBaba, Voidxor, Saber-wyn, Bucketsofg, Bota47, Jeh, Daniel C, Light current, PTSE, Tabby, E Wing, Shawnc, Georey.landis, SorryGuy, Nimbex, Whouk,Charlie Tango, Lunarsurface, Some guy, SmackBot, FocalPoint, Karlchwe, Derek Andrews, Herostratus, InverseHypercube, Thorseth,AndreasJS, Misto, Eskimbot, Nil Einne, Antifumo, Polaron, Chris the speller, Agateller, JesseStone, Oli Filth, EncMstr, Fluri, AnalogueKid, Adpete, Nbarth, Chendy, Dethme0w, Can't sleep, clown will eat me, Jacob Poon, OrphanBot, JonHarder, Xmastree, VMS Mosaic,Bassman2, Fuhghettaboutit, Jwy, LMF5000, Steve Hart, Dcamp314, DMacks, Jna runn, P373r, Dogears, DJIndica, Bige1977, Theundertow, Anlace, John, General Ization, J 1982, Jaganath, Mgiganteus1, Peterlewis, Cielomobile, CoolKoon, Ckatz, Oby1, Soulkeeper,Slakr, Beetstra, Monni95, NJA, Peter Horn, JoeBot, Linkspamremover, Ziusudra, Rsteif, D'lin, Chetvorno, Vaughan Pratt, CRGreathouse,CmdrObot, Van helsing, Smile4ru, Cydebot, Peripitus, Kairotic, KarolS, Uniqueuponhim, Tawkerbot4, Punainen Nrtti, Andrewdmartin,Trev M, Saintrain, Ozguy89, Thijs!bot, Pajz, N5iln, Drmemory, Chris01720, Electron9, Thomprod, Mailseth, Nick Number, CarbonX,Pap3rw8, Dawnseeker2000, Enyc, RoboServien, Trengarasu, Mentisto, AntiVandalBot, Majorly, Gioto, Saimhe, Guy Macon, Opelio,Gh5046, Kuteni, Res2216restar, JAnDbot, WmRowan, 100DashSix, Easchi, Magioladitis, Bongwarrior, VoABot II, Yandman, Ap-praiser, Tomhannen, Cableguyjim, Kevinmon, Gutzmer, SandStone, Thibbs, Spellmaster, Halogenated, DerHexer, JaGa, WLU, Pinokijo,Cheesebyproduct, Yobol, Hdt83, MartinBot, Schmloof, Quickmythril, Reguiieee, SmokeySteve, Glrx, CommonsDelinker, Pekaje, GuttaPercha, Johnibravo, J.delanoy, Mindgames11, Jesant13, Achuul8er, Metrax, PolychromePlatypus, Acalamari, Michael Daly, Katalaveno,PedEye1, Darkblast93, Auegel, Mikael Hggstrm, Ephebi, ThomasNichols, Plasticup, NewEnglandYankee, Sparcules, Master shepherd,Johnnie ong, Cobi, Anatoly larkin, Atropos235, Remember the dot, Drablow, Funandtrvl, Lights, Uiew, CWii, TXiKiBoT, MilkTheImp,Shalom S., The Original Wildbear, Technopat, Hqb, Acjohns, Qxz, Qbert203, Whitepines, Piper8, Eubulides, Vladsinger, Andy Dingley,Cutemonkey77, Goldkills, Jpeeling, Buhin, Insanity Incarnate, Bitbut, C0N6R355, Bpdc 01, SieBot, Tresiden, TORQUENDB, Tim-othy Cooper, Yintan, Lumenteck, Steve19steve, Permacultura, Mickea, Carnun, Hiddenfromview, 05, Macy, Ablamp, AnchorLink Bot, Tuntable, Leezahester, Dlrohrer2003, ClueBot, HujiBot, LP-mn, The Thing That Should Not Be, TinyMark, Techdawg667,EoGuy, Wysprgr2005, GreenSpigot, Mild Bill Hiccup, Uncle Milty, Sebokmike, Niceguyedc, Shjacks45, Drewster1829, Excirial, Life-ofFred, 12 Noon, MorrisRob, LarryMorseDCOhio, Iohannes Animosus, Tnxman307, WWriter, Aprout, 7, Versus22, GrahamDo, Eliz-abeth.baer, SoxBot III, Ostinato2, Weckmansj, Ginbot86, Strix nihildom, DumZiBoT, XLinkBot, Mjharrison, Theultimatezone, Time-ToSell, Little Mountain 5, NellieBly, Badgernet, JinJian, Alchaemist, TheMINT400, Addbot, Cantaloupe2, Freakmighty, DOI bot, En-ergyqueen, Shirtwaist, Favonian, Berkunt, Tide rolls, Lightbot, , TinaTimpton~enwiki, Lucacalciatore, DK4, Ben Ben, Legobot,Yobot, Zaereth, Themfromspace, Neotesla, Paraballo, A Stop at Willoughby, Amicon, AnomieBOT, BassmanIII, Kcgrant, Jim1138,Kingpin13, Mahmudmasri, Citation bot, Akilaa, Awinbisa, Sadrettin, Clark89, Quebec99, Jagcat98, Bluppen, Richard A Hall, Placid-vortex, Capricorn42, Etoombs, Kidcharlemagne101, J04n, ELIOT2000, Letsgoridebikes, SPKirsch, Rainald62, Natural Cut, Krrish23,Mishka.medvezhonok, FrescoBot, Tobby72, Hobsonlane, RicHard-59, JuniperisCommunis, Idyllic press, HJ Mitchell, Citation bot 1,Chenopodiaceous, Pinethicket, I dream of horses, Adlerbot, Fosekfotos, Tom.Reding, Calmer Waters, Pegasus33, Jschnur, Mifsud26,Gigantor205, Symppis, IJBall, DrLit, Khaotika, Alexey Goral~enwiki, Tbhotch, Minimac, DARTH SIDIOUS 2, RjwilmsiBot, Dirt-poorwizard, Jackehammond, Nmartin1, Bamaslamma1003, Teravolt, Slon02, EmausBot, Energy Dome, John of Reading, Annunciation,Chastitywest, Bigbird900, GoingBatty, K6ka, Richardop3, Thecheesykid, Drewpoleon, Mz7, Aura Light UK, Selladour, Westley Turner,H3llBot, X bvansanten X, , Donner60, DASHBotAV, 28bot, Autisexp235, ClueBot NG, Gareth Grith-Jones, Jen-ova20, Brendon12291, DieSwartzPunkt, Maverick kim, Castncoot, Widr, GlassLadyBug, Reify-tech, Amir Fatkullin, CasualVisitor, ShakirAhmed73, Boggle987, Helpful Pixie Bot, Calabe1992, Wbm1058, Alavanca~enwiki, Nature4, Silvrous, CitationCleanerBot, Emanukel,Michaelkevinjackson, Cocacolaisbetterthanpepsi, BattyBot, Crankyfrank, ChrisGualtieri, Tagremover, Webclient101, 331dot, JRYon, Big-Matow, Pravito, Djaiprakash naidu, Lewis Goudy, Lucas.wogernese, Monkbot, Kenji Higurashi, Cdot25, MEGUSTANADAAARR, Het-alia paris12, Croakobsidian, Lcso2015, ZackQB, KasparBot, Stephwarden1234, D8A-DUDE and Anonymous: 728

14.2 Images File:65W_SRS_fluorescent_lamp_starting.OGG Source: http://upload.wikimedia.org/wikipedia/commons/9/95/65W_SRS_

fluorescent_lamp_starting.OGG Lic