Light - Wikipedia

Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is perceived by the human eye. Visible light is ... Light FromWikipedia,thefreeencyclopedia Jumptonavigation Jumptosearch Electromagneticradiationthatisvisibletohumaneyes "Visiblelight"redirectshere.Forotheruses,seeLight(disambiguation)andVisiblelight(disambiguation). Atriangularprismdispersingabeamofwhitelight.Thelongerwavelengths(red)andtheshorterwavelengths(blue)areseparated. Modernphysics H ^ | ψ n ( t ) ⟩ = i ℏ ∂ ∂ t | ψ n ( t ) ⟩ {\displaystyle{\hat{H}}|\psi_{n}(t)\rangle=i\hbar{\frac{\partial}{\partialt}}|\psi_{n}(t)\rangle} G μ ν + Λ g μ ν = κ T μ ν {\displaystyleG_{\mu\nu}+\Lambdag_{\mu\nu}={\kappa}T_{\mu\nu}} SchrödingerandEinsteinfieldequations FoundersMaxPlanck ·AlbertEinstein ·NielsBohr ·MaxBorn ·WernerHeisenberg ·ErwinSchrödinger ·PascualJordan ·WolfgangPauli ·PaulDirac ·ErnestRutherford ·LouisdeBroglie ·SatyendraNathBose ConceptsTopology ·Space ·Time ·Energy ·Matter ·WorkRandomness ·Information ·Entropy ·MindLight ·Particle ·Wave BranchesApplied ·Experimental ·TheoreticalMathematical ·PhilosophyofphysicsQuantummechanics(Quantumfieldtheory ·Quantuminformation ·Quantumcomputation)Electromagnetism ·Weakinteraction ·ElectroweakinteractionStronginteractionAtomic ·Particle ·NuclearAtomic,molecular,andopticalCondensedmatter ·StatisticalComplexsystems ·Non-lineardynamics ·BiophysicsNeurophysicsPlasmaphysicsSpecialrelativity ·GeneralrelativityAstrophysics ·CosmologyTheoriesofgravitationQuantumgravity ·Theoryofeverything ScientistsWitten ·Röntgen ·Becquerel ·Lorentz ·Planck ·Curie ·Wien ·Skłodowska-Curie ·Sommerfeld ·Rutherford ·Soddy ·Onnes ·Einstein ·Wilczek ·Born ·Weyl ·Bohr ·Kramers ·Schrödinger ·deBroglie ·Laue ·Bose ·Compton ·Pauli ·Walton ·Fermi ·vanderWaals ·Heisenberg ·Dyson ·Zeeman ·Moseley ·Hilbert ·Gödel ·Jordan ·Dirac ·Wigner ·Hawking ·P.W.Anderson ·Lemaître ·Thomson ·Poincaré ·Wheeler ·Penrose ·Millikan ·Nambu ·vonNeumann ·Higgs ·Hahn ·Feynman ·Yang ·Lee ·Lenard ·Salam ·'tHooft ·Veltman ·Bell ·Gell-Mann ·J.J.Thomson ·Raman ·Bragg ·Bardeen ·Shockley ·Chadwick ·Lawrence ·Zeilinger ·Goudsmit ·Uhlenbeck CategoriesModernphysics vte Lightorvisiblelightiselectromagneticradiationwithintheportionoftheelectromagneticspectrumthatisperceivedbythehumaneye.[1]Visiblelightisusuallydefinedashavingwavelengthsintherangeof400–700nanometres(nm),correspondingtofrequenciesof750-420terahertz,betweentheinfrared(withlongerwavelengths)andtheultraviolet(withshorterwavelengths).[2][3] Inphysics,theterm"light"mayrefermorebroadlytoelectromagneticradiationofanywavelength,whethervisibleornot.[4][5]Inthissense,gammarays,X-rays,microwavesandradiowavesarealsolight.Theprimarypropertiesoflightareintensity,propagationdirection,frequencyorwavelengthspectrumandpolarization.Itsspeedinavacuum,299792458metresasecond(m/s),isoneofthefundamentalconstantsofnature.[6]Likealltypesofelectromagneticradiation,visiblelightpropagatesbymasslesselementaryparticlescalledphotonsthatrepresentsthequantaofelectromagneticfield,andcanbeanalyzedasbothwavesandparticles.Thestudyoflight,knownasoptics,isanimportantresearchareainmodernphysics. ThemainsourceofnaturallightonEarthistheSun.Historically,anotherimportantsourceoflightforhumanshasbeenfire,fromancientcampfirestomodernkerosenelamps.Withthedevelopmentofelectriclightsandpowersystems,electriclightinghaseffectivelyreplacedfirelight. Contents 1Electromagneticspectrumandvisiblelight 2Speedoflight 3Optics 3.1Refraction 4Lightsources 5Measurement 6Lightpressure 7Historicaltheoriesaboutlight,inchronologicalorder 7.1ClassicalGreeceandHellenism 7.2ClassicalIndia 7.3Descartes 7.4Particletheory 7.5Wavetheory 7.6Electromagnetictheory 7.7Quantumtheory 8UseforlightonEarth 9Seealso 10Notes 11References 12Externallinks Electromagneticspectrumandvisiblelight Theelectromagneticspectrum,withthevisibleportionhighlighted Mainarticle:Electromagneticspectrum Generally,electromagneticradiation(EMR)isclassifiedbywavelengthintoradiowaves,microwaves,infrared,thevisiblespectrumthatweperceiveaslight,ultraviolet,X-raysandgammarays.Thedesignation"radiation"excludesstaticelectric,magneticandnearfields. ThebehaviorofEMRdependsonitswavelength.Higherfrequencieshaveshorterwavelengthsandlowerfrequencieshavelongerwavelengths.WhenEMRinteractswithsingleatomsandmolecules,itsbehaviordependsontheamountofenergyperquantumitcarries. EMRinthevisiblelightregionconsistsofquanta(calledphotons)thatareatthelowerendoftheenergiesthatarecapableofcausingelectronicexcitationwithinmolecules,whichleadstochangesinthebondingorchemistryofthemolecule.Atthelowerendofthevisiblelightspectrum,EMRbecomesinvisibletohumans(infrared)becauseitsphotonsnolongerhaveenoughindividualenergytocausealastingmolecularchange(achangeinconformation)inthevisualmoleculeretinalinthehumanretina,whichchangetriggersthesensationofvision. Thereexistanimalsthataresensitivetovarioustypesofinfrared,butnotbymeansofquantum-absorption.Infraredsensinginsnakesdependsonakindofnaturalthermalimaging,inwhichtinypacketsofcellularwaterareraisedintemperaturebytheinfraredradiation.EMRinthisrangecausesmolecularvibrationandheatingeffects,whichishowtheseanimalsdetectit. Abovetherangeofvisiblelight,ultravioletlightbecomesinvisibletohumans,mostlybecauseitisabsorbedbythecorneabelow360nmandtheinternallensbelow400 nm.Furthermore,therodsandconeslocatedintheretinaofthehumaneyecannotdetecttheveryshort(below360 nm)ultravioletwavelengthsandareinfactdamagedbyultraviolet.Manyanimalswitheyesthatdonotrequirelenses(suchasinsectsandshrimp)areabletodetectultraviolet,byquantumphoton-absorptionmechanisms,inmuchthesamechemicalwaythathumansdetectvisiblelight. Varioussourcesdefinevisiblelightasnarrowlyas420–680 nm[7][8]toasbroadlyas380–800 nm.[9][10]Underideallaboratoryconditions,peoplecanseeinfrareduptoatleast1,050 nm;[11]childrenandyoungadultsmayperceiveultravioletwavelengthsdowntoabout310–313 nm.[12][13][14] Plantgrowthisalsoaffectedbythecolourspectrumoflight,aprocessknownasphotomorphogenesis. Speedoflight Mainarticle:Speedoflight BeamofsunlightinsidethecavityofRoccaill'AbissuatFondachelli-Fantina,Sicily Thespeedoflightinavacuumisdefinedtobeexactly299792458 m/s(approx.186,282milespersecond).ThefixedvalueofthespeedoflightinSIunitsresultsfromthefactthatthemetreisnowdefinedintermsofthespeedoflight.Allformsofelectromagneticradiationmoveatexactlythissamespeedinvacuum. Differentphysicistshaveattemptedtomeasurethespeedoflightthroughouthistory.Galileoattemptedtomeasurethespeedoflightintheseventeenthcentury.AnearlyexperimenttomeasurethespeedoflightwasconductedbyOleRømer,aDanishphysicist,in1676.Usingatelescope,RømerobservedthemotionsofJupiterandoneofitsmoons,Io.NotingdiscrepanciesintheapparentperiodofIo'sorbit,hecalculatedthatlighttakesabout22minutestotraversethediameterofEarth'sorbit.[15]However,itssizewasnotknownatthattime.IfRømerhadknownthediameteroftheEarth'sorbit,hewouldhavecalculatedaspeedof227000000 m/s. AnothermoreaccuratemeasurementofthespeedoflightwasperformedinEuropebyHippolyteFizeauin1849.[16]Fizeaudirectedabeamoflightatamirrorseveralkilometersaway.Arotatingcogwheelwasplacedinthepathofthelightbeamasittraveledfromthesource,tothemirrorandthenreturnedtoitsorigin.Fizeaufoundthatatacertainrateofrotation,thebeamwouldpassthroughonegapinthewheelonthewayoutandthenextgaponthewayback.Knowingthedistancetothemirror,thenumberofteethonthewheelandtherateofrotation,Fizeauwasabletocalculatethespeedoflightas313000000 m/s. LéonFoucaultcarriedoutanexperimentwhichusedrotatingmirrorstoobtainavalueof298000000 m/s[16]in1862.AlbertA.Michelsonconductedexperimentsonthespeedoflightfrom1877untilhisdeathin1931.HerefinedFoucault'smethodsin1926usingimprovedrotatingmirrorstomeasurethetimeittooklighttomakearoundtripfromMountWilsontoMountSanAntonioinCalifornia.Theprecisemeasurementsyieldedaspeedof299796000 m/s.[17] Theeffectivevelocityoflightinvarioustransparentsubstancescontainingordinarymatter,islessthaninvacuum.Forexample,thespeedoflightinwaterisabout3/4ofthatinvacuum. Twoindependentteamsofphysicistsweresaidtobringlighttoa"completestandstill"bypassingitthroughaBose–Einsteincondensateoftheelementrubidium,oneteamatHarvardUniversityandtheRowlandInstituteforScienceinCambridge,MassachusettsandtheotherattheHarvard–SmithsonianCenterforAstrophysics,alsoinCambridge.[18]However,thepopulardescriptionoflightbeing"stopped"intheseexperimentsrefersonlytolightbeingstoredintheexcitedstatesofatoms,thenre-emittedatanarbitrarylatertime,asstimulatedbyasecondlaserpulse.Duringthetimeithad"stopped"ithadceasedtobelight. Optics Mainarticle:Optics Thestudyoflightandtheinteractionoflightandmatteristermedoptics.Theobservationandstudyofopticalphenomenasuchasrainbowsandtheauroraborealisoffermanycluesastothenatureoflight. Refraction Mainarticle:Refraction Duetorefraction,thestrawdippedinwaterappearsbentandtherulerscalecompressedwhenviewedfromashallowangle. Refractionisthebendingoflightrayswhenpassingthroughasurfacebetweenonetransparentmaterialandanother.ItisdescribedbySnell'sLaw: n 1 sin ⁡ θ 1 = n 2 sin ⁡ θ 2   . {\displaystylen_{1}\sin\theta_{1}=n_{2}\sin\theta_{2}\.} whereθ1istheanglebetweentherayandthesurfacenormalinthefirstmedium,θ2istheanglebetweentherayandthesurfacenormalinthesecondmediumandn1andn2aretheindicesofrefraction,n=1inavacuumandn>1inatransparentsubstance. Whenabeamoflightcrossestheboundarybetweenavacuumandanothermedium,orbetweentwodifferentmedia,thewavelengthofthelightchanges,butthefrequencyremainsconstant.Ifthebeamoflightisnotorthogonal(orrathernormal)totheboundary,thechangeinwavelengthresultsinachangeinthedirectionofthebeam.Thischangeofdirectionisknownasrefraction. Therefractivequalityoflensesisfrequentlyusedtomanipulatelightinordertochangetheapparentsizeofimages.Magnifyingglasses,spectacles,contactlenses,microscopesandrefractingtelescopesareallexamplesofthismanipulation. Lightsources "Lightsource"redirectshere.ForthesolarenergydevelopernamedLightsource,seeLightsourceRenewableEnergy.ForaparticleacceleratorusedtogenerateX-rays,seeSynchrotronlightsource. Furtherinformation:Listoflightsources Therearemanysourcesoflight.Abodyatagiventemperatureemitsacharacteristicspectrumofblack-bodyradiation.Asimplethermalsourceissunlight,theradiationemittedbythechromosphereoftheSunataround6,000kelvins(5,730degreesCelsius;10,340degreesFahrenheit)peaksinthevisibleregionoftheelectromagneticspectrumwhenplottedinwavelengthunits[19]androughly44%ofsunlightenergythatreachesthegroundisvisible.[20]Anotherexampleisincandescentlightbulbs,whichemitonlyaround10%oftheirenergyasvisiblelightandtheremainderasinfrared.Acommonthermallightsourceinhistoryistheglowingsolidparticlesinflames,butthesealsoemitmostoftheirradiationintheinfraredandonlyafractioninthevisiblespectrum. Thepeakoftheblack-bodyspectrumisinthedeepinfrared,atabout10micrometrewavelength,forrelativelycoolobjectslikehumanbeings.Asthetemperatureincreases,thepeakshiftstoshorterwavelengths,producingfirstaredglow,thenawhiteoneandfinallyablue-whitecolourasthepeakmovesoutofthevisiblepartofthespectrumandintotheultraviolet.Thesecolourscanbeseenwhenmetalisheatedto"redhot"or"whitehot".Blue-whitethermalemissionisnotoftenseen,exceptinstars(thecommonlyseenpure-bluecolourinagasflameorawelder'storchisinfactduetomolecularemission,notablybyCHradicals(emittingawavelengthbandaround425 nmandisnotseeninstarsorpurethermalradiation). Atomsemitandabsorblightatcharacteristicenergies.Thisproduces"emissionlines"inthespectrumofeachatom.Emissioncanbespontaneous,asinlight-emittingdiodes,gasdischargelamps(suchasneonlampsandneonsigns,mercury-vaporlamps,etc.)andflames(lightfromthehotgasitself—so,forexample,sodiuminagasflameemitscharacteristicyellowlight).Emissioncanalsobestimulated,asinalaseroramicrowavemaser. Decelerationofafreechargedparticle,suchasanelectron,canproducevisibleradiation:cyclotronradiation,synchrotronradiationandbremsstrahlungradiationareallexamplesofthis.ParticlesmovingthroughamediumfasterthanthespeedoflightinthatmediumcanproducevisibleCherenkovradiation.Certainchemicalsproducevisibleradiationbychemoluminescence.Inlivingthings,thisprocessiscalledbioluminescence.Forexample,firefliesproducelightbythismeansandboatsmovingthroughwatercandisturbplanktonwhichproduceaglowingwake. Certainsubstancesproducelightwhentheyareilluminatedbymoreenergeticradiation,aprocessknownasfluorescence.Somesubstancesemitlightslowlyafterexcitationbymoreenergeticradiation.Thisisknownasphosphorescence.Phosphorescentmaterialscanalsobeexcitedbybombardingthemwithsubatomicparticles.Cathodoluminescenceisoneexample.Thismechanismisusedincathode-raytubetelevisionsetsandcomputermonitors. HongKongilluminatedbycolourfulartificiallighting. Certainothermechanismscanproducelight: Bioluminescence Cherenkovradiation Electroluminescence Scintillation Sonoluminescence Triboluminescence Whentheconceptoflightisintendedtoincludevery-high-energyphotons(gammarays),additionalgenerationmechanismsinclude: Particle–antiparticleannihilation Radioactivedecay Measurement Mainarticles:Photometry(optics)andRadiometry Lightismeasuredwithtwomainalternativesetsofunits:radiometryconsistsofmeasurementsoflightpoweratallwavelengths,whilephotometrymeasureslightwithwavelengthweightedwithrespecttoastandardizedmodelofhumanbrightnessperception.Photometryisuseful,forexample,toquantifyIllumination(lighting)intendedforhumanuse. Thephotometryunitsaredifferentfrommostsystemsofphysicalunitsinthattheytakeintoaccounthowthehumaneyerespondstolight.Theconecellsinthehumaneyeareofthreetypeswhichresponddifferentlyacrossthevisiblespectrumandthecumulativeresponsepeaksatawavelengthofaround555 nm.Therefore,twosourcesoflightwhichproducethesameintensity(W/m2)ofvisiblelightdonotnecessarilyappearequallybright.Thephotometryunitsaredesignedtotakethisintoaccountandthereforeareabetterrepresentationofhow"bright"alightappearstobethanrawintensity.Theyrelatetorawpowerbyaquantitycalledluminousefficacyandareusedforpurposeslikedetermininghowtobestachievesufficientilluminationforvarioustasksinindoorandoutdoorsettings.Theilluminationmeasuredbyaphotocellsensordoesnotnecessarilycorrespondtowhatisperceivedbythehumaneyeandwithoutfilterswhichmaybecostly,photocellsandcharge-coupleddevices(CCD)tendtorespondtosomeinfrared,ultravioletorboth. Lightpressure Mainarticle:Radiationpressure Lightexertsphysicalpressureonobjectsinitspath,aphenomenonwhichcanbededucedbyMaxwell'sequations,butcanbemoreeasilyexplainedbytheparticlenatureoflight:photonsstrikeandtransfertheirmomentum.Lightpressureisequaltothepowerofthelightbeamdividedbyc,thespeedoflight. Duetothemagnitudeofc,theeffectoflightpressureisnegligibleforeverydayobjects. Forexample,aone-milliwattlaserpointerexertsaforceofabout3.3piconewtonsontheobjectbeingilluminated;thus,onecouldliftaU.S.pennywithlaserpointers,butdoingsowouldrequireabout30 billion1-mWlaserpointers.[21] However,innanometre-scaleapplicationssuchasnanoelectromechanicalsystems(NEMS),theeffectoflightpressureismoresignificantandexploitinglightpressuretodriveNEMSmechanismsandtoflipnanometre-scalephysicalswitchesinintegratedcircuitsisanactiveareaofresearch.[22]Atlargerscales,lightpressurecancauseasteroidstospinfaster,[23]actingontheirirregularshapesasonthevanesofawindmill. Thepossibilityofmakingsolarsailsthatwouldacceleratespaceshipsinspaceisalsounderinvestigation.[24][25] AlthoughthemotionoftheCrookesradiometerwasoriginallyattributedtolightpressure,thisinterpretationisincorrect;thecharacteristicCrookesrotationistheresultofapartialvacuum.[26]ThisshouldnotbeconfusedwiththeNicholsradiometer,inwhichthe(slight)motioncausedbytorque(thoughnotenoughforfullrotationagainstfriction)isdirectlycausedbylightpressure.[27] Asaconsequenceoflightpressure,Einstein[28]in1909predictedtheexistenceof"radiationfriction"whichwouldopposethemovementofmatter.Hewrote,"radiationwillexertpressureonbothsidesoftheplate.Theforcesofpressureexertedonthetwosidesareequaliftheplateisatrest.However,ifitisinmotion,moreradiationwillbereflectedonthesurfacethatisaheadduringthemotion(frontsurface)thanonthebacksurface.Thebackwardactingforceofpressureexertedonthefrontsurfaceisthuslargerthantheforceofpressureactingontheback.Hence,astheresultantofthetwoforces,thereremainsaforcethatcounteractsthemotionoftheplateandthatincreaseswiththevelocityoftheplate.Wewillcallthisresultant'radiationfriction'inbrief." Usuallylightmomentumisalignedwithitsdirectionofmotion.However,forexampleinevanescentwavesmomentumistransversetodirectionofpropagation.[29] Historicaltheoriesaboutlight,inchronologicalorder ClassicalGreeceandHellenism InthefifthcenturyBC,Empedoclespostulatedthateverythingwascomposedoffourelements;fire,air,earthandwater.HebelievedthatAphroditemadethehumaneyeoutofthefourelementsandthatshelitthefireintheeyewhichshoneoutfromtheeyemakingsightpossible.Ifthisweretrue,thenonecouldseeduringthenightjustaswellasduringtheday,soEmpedoclespostulatedaninteractionbetweenraysfromtheeyesandraysfromasourcesuchasthesun.[30] Inabout300BC,EuclidwroteOptica,inwhichhestudiedthepropertiesoflight.Euclidpostulatedthatlighttravelledinstraightlinesandhedescribedthelawsofreflectionandstudiedthemmathematically.Hequestionedthatsightistheresultofabeamfromtheeye,forheaskshowoneseesthestarsimmediately,ifoneclosesone'seyes,thenopensthematnight.Ifthebeamfromtheeyetravelsinfinitelyfastthisisnotaproblem.[31] In55BC,Lucretius,aRomanwhocarriedontheideasofearlierGreekatomists,wrotethat"Thelight&heatofthesun;thesearecomposedofminuteatomswhich,whentheyareshovedoff,losenotimeinshootingrightacrosstheinterspaceofairinthedirectionimpartedbytheshove."(fromOnthenatureoftheUniverse).Despitebeingsimilartolaterparticletheories,Lucretius'sviewswerenotgenerallyaccepted.Ptolemy(c.secondcentury)wroteabouttherefractionoflightinhisbookOptics.[32] ClassicalIndia InancientIndia,theHinduschoolsofSamkhyaandVaisheshika,fromaroundtheearlycenturiesADdevelopedtheoriesonlight.AccordingtotheSamkhyaschool,lightisoneofthefivefundamental"subtle"elements(tanmatra)outofwhichemergethegrosselements.Theatomicityoftheseelementsisnotspecificallymentionedanditappearsthattheywereactuallytakentobecontinuous.[33] Ontheotherhand,theVaisheshikaschoolgivesanatomictheoryofthephysicalworldonthenon-atomicgroundofether,spaceandtime.(SeeIndianatomism.)Thebasicatomsarethoseofearth(prthivi),water(pani),fire(agni)andair(vayu)Lightraysaretakentobeastreamofhighvelocityoftejas(fire)atoms.Theparticlesoflightcanexhibitdifferentcharacteristicsdependingonthespeedandthearrangementsofthetejasatoms.[citationneeded] TheVishnuPuranareferstosunlightas"thesevenraysofthesun".[33] TheIndianBuddhists,suchasDignāgainthefifthcenturyandDharmakirtiintheseventhcentury,developedatypeofatomismthatisaphilosophyaboutrealitybeingcomposedofatomicentitiesthataremomentaryflashesoflightorenergy.Theyviewedlightasbeinganatomicentityequivalenttoenergy.[33] Descartes RenéDescartes(1596–1650)heldthatlightwasamechanicalpropertyoftheluminousbody,rejectingthe"forms"ofIbnal-HaythamandWiteloaswellasthe"species"ofBacon,GrossetesteandKepler.[34]In1637hepublishedatheoryoftherefractionoflightthatassumed,incorrectly,thatlighttravelledfasterinadensermediumthaninalessdensemedium.Descartesarrivedatthisconclusionbyanalogywiththebehaviourofsoundwaves.[citationneeded]AlthoughDescarteswasincorrectabouttherelativespeeds,hewascorrectinassumingthatlightbehavedlikeawaveandinconcludingthatrefractioncouldbeexplainedbythespeedoflightindifferentmedia. Descartesisnotthefirsttousethemechanicalanalogiesbutbecauseheclearlyassertsthatlightisonlyamechanicalpropertyoftheluminousbodyandthetransmittingmedium,Descartes'stheoryoflightisregardedasthestartofmodernphysicaloptics.[34] Particletheory Mainarticle:Corpusculartheoryoflight PierreGassendi. PierreGassendi(1592–1655),anatomist,proposedaparticletheoryoflightwhichwaspublishedposthumouslyinthe1660s.IsaacNewtonstudiedGassendi'sworkatanearlyageandpreferredhisviewtoDescartes'stheoryoftheplenum.HestatedinhisHypothesisofLightof1675thatlightwascomposedofcorpuscles(particlesofmatter)whichwereemittedinalldirectionsfromasource.OneofNewton'sargumentsagainstthewavenatureoflightwasthatwaveswereknowntobendaroundobstacles,whilelighttravelledonlyinstraightlines.Hedid,however,explainthephenomenonofthediffractionoflight(whichhadbeenobservedbyFrancescoGrimaldi)byallowingthatalightparticlecouldcreatealocalisedwaveintheaether. Newton'stheorycouldbeusedtopredictthereflectionoflight,butcouldonlyexplainrefractionbyincorrectlyassumingthatlightaccelerateduponenteringadensermediumbecausethegravitationalpullwasgreater.NewtonpublishedthefinalversionofhistheoryinhisOpticksof1704.Hisreputationhelpedtheparticletheoryoflighttoholdswayduringthe18thcentury.TheparticletheoryoflightledLaplacetoarguethatabodycouldbesomassivethatlightcouldnotescapefromit.Inotherwords,itwouldbecomewhatisnowcalledablackhole.Laplacewithdrewhissuggestionlater,afterawavetheoryoflightbecamefirmlyestablishedasthemodelforlight(ashasbeenexplained,neitheraparticleorwavetheoryisfullycorrect).AtranslationofNewton'sessayonlightappearsinThelargescalestructureofspace-time,byStephenHawkingandGeorgeF.R.Ellis. ThefactthatlightcouldbepolarizedwasforthefirsttimequalitativelyexplainedbyNewtonusingtheparticletheory.Étienne-LouisMalusin1810createdamathematicalparticletheoryofpolarization.Jean-BaptisteBiotin1812showedthatthistheoryexplainedallknownphenomenaoflightpolarization.Atthattimethepolarizationwasconsideredastheproofoftheparticletheory. Wavetheory Toexplaintheoriginofcolours,RobertHooke(1635–1703)developeda"pulsetheory"andcomparedthespreadingoflighttothatofwavesinwaterinhis1665workMicrographia("ObservationIX").In1672Hookesuggestedthatlight'svibrationscouldbeperpendiculartothedirectionofpropagation.ChristiaanHuygens(1629–1695)workedoutamathematicalwavetheoryoflightin1678andpublisheditinhisTreatiseonlightin1690.Heproposedthatlightwasemittedinalldirectionsasaseriesofwavesinamediumcalledtheluminiferousaether.Aswavesarenotaffectedbygravity,itwasassumedthattheysloweddownuponenteringadensermedium.[35] ChristiaanHuygens. ThomasYoung'ssketchofadouble-slitexperimentshowingdiffraction.Young'sexperimentssupportedthetheorythatlightconsistsofwaves. Thewavetheorypredictedthatlightwavescouldinterferewitheachotherlikesoundwaves(asnotedaround1800byThomasYoung).Youngshowedbymeansofadiffractionexperimentthatlightbehavedaswaves.Healsoproposedthatdifferentcolourswerecausedbydifferentwavelengthsoflightandexplainedcolourvisionintermsofthree-colouredreceptorsintheeye.AnothersupporterofthewavetheorywasLeonhardEuler.HearguedinNovatheorialucisetcolorum(1746)thatdiffractioncouldmoreeasilybeexplainedbyawavetheory.In1816André-MarieAmpèregaveAugustin-JeanFresnelanideathatthepolarizationoflightcanbeexplainedbythewavetheoryiflightwereatransversewave.[36] Later,FresnelindependentlyworkedouthisownwavetheoryoflightandpresentedittotheAcadémiedesSciencesin1817.SiméonDenisPoissonaddedtoFresnel'smathematicalworktoproduceaconvincingargumentinfavorofthewavetheory,helpingtooverturnNewton'scorpusculartheory.[dubious–discuss]Bytheyear1821,Fresnelwasabletoshowviamathematicalmethodsthatpolarizationcouldbeexplainedbythewavetheoryoflightifandonlyiflightwasentirelytransverse,withnolongitudinalvibrationwhatsoever.[citationneeded] Theweaknessofthewavetheorywasthatlightwaves,likesoundwaves,wouldneedamediumfortransmission.TheexistenceofthehypotheticalsubstanceluminiferousaetherproposedbyHuygensin1678wascastintostrongdoubtinthelatenineteenthcenturybytheMichelson–Morleyexperiment. Newton'scorpusculartheoryimpliedthatlightwouldtravelfasterinadensermedium,whilethewavetheoryofHuygensandothersimpliedtheopposite.Atthattime,thespeedoflightcouldnotbemeasuredaccuratelyenoughtodecidewhichtheorywascorrect.ThefirsttomakeasufficientlyaccuratemeasurementwasLéonFoucault,in1850.[37]Hisresultsupportedthewavetheoryandtheclassicalparticletheorywasfinallyabandoned,onlytopartlyre-emergeinthe20thcentury. Electromagnetictheory Mainarticle:Electromagneticradiation Alinearlypolarizedelectromagneticwavegoinginthex-axis,withEdenotingtheelectricfieldandperpendicularBdenotingmagneticfield In1845,MichaelFaradaydiscoveredthattheplaneofpolarizationoflinearlypolarizedlightisrotatedwhenthelightraystravelalongthemagneticfielddirectioninthepresenceofatransparentdielectric,aneffectnowknownasFaradayrotation.[38]Thiswasthefirstevidencethatlightwasrelatedtoelectromagnetism.In1846hespeculatedthatlightmightbesomeformofdisturbancepropagatingalongmagneticfieldlines.[38]Faradayproposedin1847thatlightwasahigh-frequencyelectromagneticvibration,whichcouldpropagateevenintheabsenceofamediumsuchastheether.[39] Faraday'sworkinspiredJamesClerkMaxwelltostudyelectromagneticradiationandlight.Maxwelldiscoveredthatself-propagatingelectromagneticwaveswouldtravelthroughspaceataconstantspeed,whichhappenedtobeequaltothepreviouslymeasuredspeedoflight.Fromthis,Maxwellconcludedthatlightwasaformofelectromagneticradiation:hefirststatedthisresultin1862inOnPhysicalLinesofForce.In1873,hepublishedATreatiseonElectricityandMagnetism,whichcontainedafullmathematicaldescriptionofthebehaviorofelectricandmagneticfields,stillknownasMaxwell'sequations.Soonafter,HeinrichHertzconfirmedMaxwell'stheoryexperimentallybygeneratinganddetectingradiowavesinthelaboratoryanddemonstratingthatthesewavesbehavedexactlylikevisiblelight,exhibitingpropertiessuchasreflection,refraction,diffractionandinterference.Maxwell'stheoryandHertz'sexperimentsleddirectlytothedevelopmentofmodernradio,radar,television,electromagneticimagingandwirelesscommunications. Inthequantumtheory,photonsareseenaswavepacketsofthewavesdescribedintheclassicaltheoryofMaxwell.ThequantumtheorywasneededtoexplaineffectsevenwithvisuallightthatMaxwell'sclassicaltheorycouldnot(suchasspectrallines). Quantumtheory In1900MaxPlanck,attemptingtoexplainblack-bodyradiation,suggestedthatalthoughlightwasawave,thesewavescouldgainorloseenergyonlyinfiniteamountsrelatedtotheirfrequency.Planckcalledthese"lumps"oflightenergy"quanta"(fromaLatinwordfor"howmuch").In1905,AlbertEinsteinusedtheideaoflightquantatoexplainthephotoelectriceffectandsuggestedthattheselightquantahada"real"existence.In1923ArthurHollyComptonshowedthatthewavelengthshiftseenwhenlowintensityX-raysscatteredfromelectrons(socalledComptonscattering)couldbeexplainedbyaparticle-theoryofX-rays,butnotawavetheory.In1926GilbertN.Lewisnamedtheselightquantaparticlesphotons.[40] Eventuallythemoderntheoryofquantummechanicscametopicturelightas(insomesense)bothaparticleandawaveand(inanothersense),asaphenomenonwhichisneitheraparticlenorawave(whichactuallyaremacroscopicphenomena,suchasbaseballsoroceanwaves).Instead,modernphysicsseeslightassomethingthatcanbedescribedsometimeswithmathematicsappropriatetoonetypeofmacroscopicmetaphor(particles)andsometimesanothermacroscopicmetaphor(waterwaves),butisactuallysomethingthatcannotbefullyimagined.AsinthecaseforradiowavesandtheX-raysinvolvedinComptonscattering,physicistshavenotedthatelectromagneticradiationtendstobehavemorelikeaclassicalwaveatlowerfrequencies,butmorelikeaclassicalparticleathigherfrequencies,butnevercompletelylosesallqualitiesofoneortheother.Visiblelight,whichoccupiesamiddlegroundinfrequency,caneasilybeshowninexperimentstobedescribableusingeitherawaveorparticlemodel,orsometimesboth. InFebruary2018,scientistsreported,forthefirsttime,thediscoveryofanewformoflight,whichmayinvolvepolaritons,thatcouldbeusefulinthedevelopmentofquantumcomputers.[41][42] UseforlightonEarth Sunlightprovidestheenergythatgreenplantsusetocreatesugarsmostlyintheformofstarches,whichreleaseenergyintothelivingthingsthatdigestthem.Thisprocessofphotosynthesisprovidesvirtuallyalltheenergyusedbylivingthings.Somespeciesofanimalsgeneratetheirownlight,aprocesscalledbioluminescence.Forexample,firefliesuselighttolocatematesandvampiresquiduseittohidethemselvesfromprey. Seealso Physicsportal Scienceportal Automotivelighting Ballisticphoton Colourtemperature Fermat'sprinciple Huygens'principle JournalofLuminescence Lightart Lightbeam–inparticularaboutlightbeamsvisiblefromtheside LightFantastic(TVseries) Lightmill Lightpainting Lightpollution Lighttherapy Lighting Listoflightsources Luminescence:TheJournalofBiologicalandChemicalLuminescence Photicsneezereflex Righttolight Risksandbenefitsofsunexposure Spectroscopy Notes References ^CIE(1987).InternationalLightingVocabularyArchived27February2010attheWaybackMachine.Number17.4.CIE,4thedition.ISBN 978-3-900734-07-7.BytheInternationalLightingVocabulary,thedefinitionoflightis:"Anyradiationcapableofcausingavisualsensationdirectly." ^Pal,G.K.;Pal,Pravati(2001)."chapter52".TextbookofPracticalPhysiology(1st ed.).Chennai:OrientBlackswan.p. 387.ISBN 978-81-250-2021-9.Retrieved11October2013.Thehumaneyehastheabilitytorespondtoallthewavelengthsoflightfrom400–700nm.Thisiscalledthevisiblepartofthespectrum. ^Buser,PierreA.;Imbert,Michel(1992).Vision.MITPress.p. 50.ISBN 978-0-262-02336-8.Retrieved11October2013.Lightisaspecialclassofradiantenergyembracingwavelengthsbetween400and700nm(ormμ),or4000to7000Å. ^GregoryHallockSmith(2006).Cameralenses:fromboxcameratodigital.SPIEPress.p. 4.ISBN 978-0-8194-6093-6. ^NarinderKumar(2008).ComprehensivePhysicsXII.LaxmiPublications.p. 1416.ISBN 978-81-7008-592-8. ^Uzan,J-P;Leclercq,B(2008).TheNaturalLawsoftheUniverse:UnderstandingFundamentalConstants.TranslatedbyRobertMizon.Springer-Praxis,InternetArchive:2020-06-14AbdzexKuban.pp. 43–4.Bibcode:2008nlu..book.....U.doi:10.1007/978-0-387-74081-2.ISBN 978-0-387-73454-5. ^Laufer,Gabriel(13July1996)."GeometricalOptics".IntroductiontoOpticsandLasersinEngineering.IntroductiontoOpticsandLasersinEngineering.p. 11.Bibcode:1996iole.book.....L.doi:10.1017/CBO9781139174190.004.ISBN 978-0-521-45233-5.Retrieved20October2013. ^Bradt,Hale(2004).AstronomyMethods:APhysicalApproachtoAstronomicalObservations.CambridgeUniversityPress.p. 26.ISBN 978-0-521-53551-9.Retrieved20October2013. ^Ohannesian,Lena;Streeter,Anthony(9November2001).HandbookofPharmaceuticalAnalysis.CRCPress.p. 187.ISBN 978-0-8247-4194-5.Retrieved20October2013. ^Ahluwalia,V.K.;Goyal,Madhuri(1January2000).ATextbookofOrganicChemistry.Narosa.p. 110.ISBN 978-81-7319-159-6.Retrieved20October2013. ^Sliney,DavidH.;Wangemann,RobertT.;Franks,JamesK.;Wolbarsht,MyronL.(1976)."Visualsensitivityoftheeyetoinfraredlaserradiation".JournaloftheOpticalSocietyofAmerica.66(4):339–341.Bibcode:1976JOSA...66..339S.doi:10.1364/JOSA.66.000339.PMID 1262982.Thefovealsensitivitytoseveralnear-infraredlaserwavelengthswasmeasured.Itwasfoundthattheeyecouldrespondtoradiationatwavelengthsatleastasfaras1,064nm.Acontinuous1,064nmlasersourceappearedred,buta1,060nmpulsedlasersourceappearedgreen,whichsuggeststhepresenceofsecondharmonicgenerationintheretina. ^Lynch,DavidK.;Livingston,WilliamCharles(2001).ColorandLightinNature(2nd ed.).Cambridge:CambridgeUniversityPress.p. 231.ISBN 978-0-521-77504-5.Retrieved12October2013.Limitsoftheeye'soverallrangeofsensitivityextendsfromabout310to1,050nanometers ^Dash,MadhabChandra;Dash,SatyaPrakash(2009).FundamentalsofEcology3E.TataMcGraw-HillEducation.p. 213.ISBN 978-1-259-08109-5.Retrieved18October2013.Normallythehumaneyerespondstolightraysfrom390to760nm.Thiscanbeextendedtoarangeof310to1,050nmunderartificialconditions. ^Saidman,Jean(15May1933)."Surlavisibilitédel'ultravioletjusqu'àlalongueurd'onde3130"[Thevisibilityoftheultraviolettothewavelengthof3130].Comptesrendusdel'Académiedessciences(inFrench).196:1537–9. ^Oldford,R.W;MacKay,R.J(2000)."ScientificMethod,StatisticalMethodandtheSpeedofLight".StatisticalScience.15(3):254–278.doi:10.1214/ss/1009212817.MR 1847825. ^abNewcomb,Simon(1911)."Light" .InChisholm,Hugh(ed.).EncyclopædiaBritannica.Vol. 16(11th ed.).CambridgeUniversityPress.p. 624. ^Michelson,A.A.(January1927)."MeasurementsofthevelocityoflightbetweenMountWilsonandMountSanAntonio".AstrophysicalJournal.65:1.Bibcode:1927ApJ....65....1M.doi:10.1086/143021. ^HarvardNewsOffice(24January2001)."HarvardGazette:Researchersnowabletostop,restartlight".News.harvard.edu.Archivedfromtheoriginalon28October2011.Retrieved8November2011. ^"SpectrumandtheColorSensitivityoftheEye"(PDF).Thulescientific.com.Retrieved29August2017. ^"ReferenceSolarSpectralIrradiance:AirMass1.5".Retrieved12November2009. ^Tang,Hong(1October2009)."MayTheForceofLightBeWithYou".IEEESpectrum.46(10):46–51.doi:10.1109/MSPEC.2009.5268000.S2CID 7928030. ^See,forexample,nano-opto-mechanicalsystemsresearchatYaleUniversity. ^Svitil,KathyA.(5February2004)."AsteroidsGetSpunBytheSun".DiscoverMagazine. ^"SolarSailsCouldSendSpacecraft'Sailing'ThroughSpace".NASA.31August2004. ^"NASAteamsuccessfullydeploystwosolarsailsystems".NASA.9August2004. ^P.Lebedev,UntersuchungenüberdieDruckkräftedesLichtes,Ann.Phys.6,433(1901). ^Nichols,E.F;Hull,G.F.(1903)."ThePressureduetoRadiation".TheAstrophysicalJournal.17(5):315–351.Bibcode:1903ApJ....17..315N.doi:10.1086/141035. ^Einstein,A.(1909).Onthedevelopmentofourviewsconcerningthenatureandconstitutionofradiation.Translatedin:TheCollectedPapersofAlbertEinstein,vol.2(PrincetonUniversityPress,Princeton,1989).Princeton,NewJersey:PrincetonUniversityPress.p. 391. ^Antognozzi,M.;Bermingham,C.R.;Harniman,R.L.;Simpson,S.;Senior,J.;Hayward,R.;Hoerber,H.;Dennis,M.R.;Bekshaev,A.Y.(August2016)."Directmeasurementsoftheextraordinaryopticalmomentumandtransversespin-dependentforceusinganano-cantilever".NaturePhysics.12(8):731–735.arXiv:1506.04248.Bibcode:2016NatPh..12..731A.doi:10.1038/nphys3732.ISSN 1745-2473.S2CID 52226942. ^Singh,S.(2009).FundamentalsofOpticalEngineering.DiscoveryPublishingHouse.ISBN 9788183564366. ^O'Connor,JJ;Robertson,EF(August2002)."Lightthroughtheages:AncientGreecetoMaxwell".Archivedfromtheoriginalon19March2017.Retrieved20February2017. ^PtolemyandA.MarkSmith(1996).Ptolemy'sTheoryofVisualPerception:AnEnglishTranslationoftheOpticswithIntroductionandCommentary.DianePublishing.p. 23.ISBN 978-0-87169-862-9. ^abc"ShastraPratibha2015SeniorsBooklet"(PDF).Sifuae.com.Retrieved29August2017. ^abTheoriesoflight,fromDescartestoNewtonA.I.SabraCUPArchive,1981p.48ISBN 0-521-28436-8,978-0-521-28436-3 ^FokkoJanDijksterhuis,LensesandWaves:ChristiaanHuygensandtheMathematicalScienceofOpticsinthe17thCentury,KluwerAcademicPublishers,2004,ISBN 1-4020-2697-8 ^JamesR.Hofmann,André-MarieAmpère:EnlightenmentandElectrodynamics,CambridgeUniversityPress,1996,p.222. ^DavidCassidy;GeraldHolton;JamesRutherford(2002).UnderstandingPhysics.Birkhäuser.ISBN 978-0-387-98756-9. ^abLongair,Malcolm(2003).TheoreticalConceptsinPhysics.p. 87. ^Cassidy,D(2002).UnderstandingPhysics.SpringerVerlagNewYork. ^Barrow,GordonM.(1962).IntroductiontoMolecularSpectroscopy(ScannedPDF).McGraw-Hill.LCCN 62-12478. ^Hignett,Katherine(16February2018)."PhysicsCreatesNewFormofLightThatCouldDriveTheQuantumComputingRevolution".Newsweek.Retrieved17February2018. ^Liang,Qi-Yu;et al.(16February2018)."Observationofthree-photonboundstatesinaquantumnonlinearmedium".Science.359(6377):783–786.arXiv:1709.01478.Bibcode:2018Sci...359..783L.doi:10.1126/science.aao7293.PMC 6467536.PMID 29449489. 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