Visible light

Introduction

In1666,BritishscientistNewtonfirstrevealedthechromaticnatureoflightandthesecretofcolor.Heusedexperimentstoshowthatsunlightisamixedlightofvariouscolors,andfoundthatthecoloroflightdependsonthefrequencyoflight.

Thenumberonthecolorringindicatesthefrequencyofthecorrespondingcolorlight.Thefrequencyunitisterahertz(THz),andthewavelengthunitisnanometer(nm).Thecolorsinanytwoopposingsectorsonthecolorringaresymmetricaltoeachother.Complementarycolor.Forexample,thecomplementarycolorofblue(480-435nm)isorange(595-580nm).

Themainnaturallightsourceofvisiblelightisthesun,andthemainartificiallightsourceisincandescentobjects(especiallyincandescentlamps).Thevisiblespectrumtheyemitiscontinuous.Thegasdischargetubealsoemitsvisiblelight,anditsspectrumisdiscrete.Variousgasdischargetubesandfiltersareoftenusedasmonochromaticlightsources.

Range

Electromagneticwaveswithdifferentfrequenciescausedifferentcolorperceptionsinhumaneyes.

Color

Frequency

Wavelength

Legend

Thefrequencyofvisiblelightis3.8×10¹⁴～7.5×10¹⁴Hz(380~750THz).

Characteristics

Throughresearch,itisfoundthatthecolorlightalsohasthefollowingcharacteristics:

1.Thecomplementarycolorsaremixedinacertainproportiontoobtainwhitelight.Forexample,bluelightandyellowlightaremixedtogetwhitelight.Inthesameway,themixtureofcyanlightandredlightisalsowhitelight.

2.Anycoloronthecolorringcanusethetwokindsofmonochromaticlightsonitsadjacentsides,andcanevenbecopiedfromthetwokindsofmonochromaticlightsofthenextneighbors.Ifyellowlightandredlightaremixedtogetorangelight.Itismoretypicalthatredlightandgreenlightmixtobecomeyellowlight.

3.Ifyouchoosethreeindependentmonochromaticlightsonthecolorring.Itcanbemixedintovarioustonesthatmayappearindailylifeindifferentproportions.Thesethreemonochromaticlightsarecalledthreeprimarycolors.Thethreeprimarycolorsinopticsarered,green,andblue.Itshouldbenotedherethatthethreeprimarycolorsofthepigmentarecyan,magenta,andyellow.However,thechoiceofthethreeprimarycolorsiscompletelyarbitrary.

4.Whenthesunlightilluminatesanobject,thelightofacertainfrequencyisabsorbedbytheobject,andthecolor(reflectedlight)displayedbytheobjectisthecomplementarycolorofthelight.Ifthesunshinesontheobject,iftheobjectabsorbsthevioletlightof435~400nm,theobjectwillappearyellow-green.

Visiblelightradiation

Visiblelightradiationgenerallyreferstotheradiationinthe0.78～0.4micronbandinthesolarradiationspectrum,consistingofred,orange,yellow,green,andblueItiscomposedofsevencolorsoflightsuchas,indigoandpurple.Itisthenecessaryandeffectivesolarradiationenergyforgreenplantstocarryoutphotosynthesis.Thevisiblelightradiationreachingthegroundsurfacevarieswithatmosphericturbidity,sunheight,cloudcoverandweatherconditions.Visiblelightradiationaccountsforabout45-50%ofthetotalradiation.

Application

Remotesensingtechnology

Visiblelightremotesensing(visiblespectralremotesensing)meansthattheworkingbandofthesensorislimitedtotherangeofvisiblelight(0.78～0.4microns)RemoteSensingTechnology.

Thevisiblelightrangeoftheelectromagneticspectrumisbetween0.78and0.4microns,whichisthemostcommonlyusedworkingbandintraditionalaerialphotographyreconnaissanceandaerialphotographysurveyingandmapping.Becausethecolorsensitivityrangeofphotosensitivefilmisjustinthisfrequencyrange,black-and-whitefull-colororcolorimageswithhighgroundresolution,interpretationandmapdrawingperformancecanbeobtained.However,duetotheextremelimitationsofthesun'silluminationconditions,coupledwiththesuccessiveemergenceofinfraredphotographyandmulti-bandremotesensing,visiblelightremotesensinghasextendedtheworkingbandtothenear-infraredregion(approximately0.9microns).Theimagingmethodhasalsodevelopedfromasinglephotographicimagingtoincludeblack-and-whitephotography,infraredphotography,colorphotography,colorinfraredphotography,multi-bandphotographyandmulti-bandscanning,anditsdetectioncapabilitieshavebeengreatlyimproved.Visiblelightremotesensing,markedbytheapplicationofframe-typeaerospacecameras,hasgreatdevelopmentpotentialforspacephotogrammetry.

Communicationtechnology

VisiblelightcommunicationtechnologyisanewgreeninformationtechnologythatusestherapidresponsecharacteristicsofLEDstoachievewirelesshigh-speeddatatransmission.Thedigitalsignalismodulatedtothepowerline,andthevisiblelightflashesquicklythroughthecommunicationmoduleinstalledintheLEDlamptorealizethetransmissionofinformation.Thiskindoffastflickerreaches300Mbit/s,andthehumaneyecannotperceivethiskindofflicker.Second,theflashinglightisreceivedbythephotosensitivedeviceatthereceivingend,andthedemodulationistheinformationthatthetransmittingendwantstotransmit.AsoneoftheInternetofThingstechnology,visiblelightcommunicationtechnologyistoprovidelightingequipmentwith"wirelessrouters","communicationbasestations","networkaccesspoints"andeven"wirelessrouters","communicationbasestations","networkaccesspoints"andeven"underthepremiseofnotaffectingnormallighting."ThefunctionofGPSsatellites.

Cloudmap

Thesatelliteobservationinstrumentsensesthereflectionofthegroundandcloudsonthesuninthevisiblelightband,anddisplaysitasaplaneimage,whichisvisiblelightcloudmapb>.Thedegreeofblackandwhiteoftheimagerepresentsthealbedoofthegroundandclouds,whitemeanshighalbedo,andblackmeanslowalbedo.Generallyspeaking,thethickerthecloud,thebrighteritsbrightness.Ifthelightingconditionsofthesunarethesame,thewaterdropletcloudisbrighterthantheicecrystalcloudforthesamethickcloud.Forexample,largeandthickclouds,especiallycumulonimbusclouds,aredensewhite;medium-thickclouds(cirrostratus,altostratus,fog,stratus,cumulus,etc.)arewhite;thinandsmallcloudareasonthecontinent(Suchascumuluscloudsonasunnyday)areoff-white,etc.

Visiblelight

Commonvisiblelightlampsincludeincandescentlamps,halogenlamps,fluorescentlamps,energy-savinglamps,LEDlamps,high-pressuresodiumlamps,metalhalidelamps,electrodelesslamps,neonlamps,etc.

Thefollowingintroducestheworkingprinciplesofseveralcommonvisiblelightlampstoillustratethevariousfrequenciesofvisiblelightradiationthatthistypeoflampsmayproduceduringdailyuse:

1.Incandescentlamps:Itsstructureistoputthefilament(singlespiralfilamentordoublespiralfilament)intotheglassshell,andaddalampcap.Thefilamentisspiralinordertoreducetheevaporationoftungsteninthefilamentandprolongitsservicelife.Generally,itisfilledintheglassshell.Theargon-nitrogenmixtureisalsousedtoreducetheevaporationoftungsteninthefilament.Whenthelampisconnectedtothecircuit,thecurrentflowsthroughthefilament,andthecurrentproducesathermaleffect,causingtheincandescentbulbtoemitcontinuousvisiblelightandinfrared.Thisphenomenoncanbenoticedwhenthefilamenttemperaturerisesto700K.ThefrequencyofthethermalradiationisfromclosetoInfrared(380THz,780nm)graduallyrisestoaboutultraviolet(750THz,400nm).Theincandescentlampisalowcolortemperaturelightsource,thecolortemperatureisgenerally2400~2900K,thecolorrenderingisbetter,thecolorrenderingindexis99~100.However,duetothehightemperatureofthefilamentduringoperation,mostoftheenergyisconsumedintheformofinfraredradiation,sotheservicelifeisshort,generallynotexceeding1000h.Amongallelectriclightingproducts,incandescentlampshavethelowestefficiency.Onlyabout2%oftheenergycanbeconvertedintolightenergy.Althoughthelightefficiencyoftheincandescentlampislow,thelightcolorandlightcollectionperformanceareverygood,anditistheelectriclightsourcewiththelargestoutputandthemostwidelyused.

2.Halogenlamp:Basedontheincandescentlamp,asmallamountofhalogenelementisaddedtothefillinggastoformanefficientsmalllightsource.Ordinaryglassshellsarealsochangedtoquartzglass,hardhighsilicaglassoraluminateglasstoovercomehightemperatures.Halogenlampshavethecharacteristicsofhighluminousefficiencyandlonglife,andthereisa"tungstenhalogencycle"inthehalogenlamp,thatis,acyclicchemicalreaction.Halogenlampsandincandescentlampsarebothheatradiationlightsourcesandradiatealotofheat.However,theintensityoflightemittedbyhalogenlampsismuchhigherthanthatofincandescentlamps,andtheenergyconsumptionisreducedbyabout1/3.Thelightemittedbythehalogenlampcontainsultravioletcomponents,whicharedividedintothreewavelengthbands:UVA,UVB,andUVC,andUVBandUVChaveableachingeffectonthesubject.WhetherthehalogenlampwillproduceUVBharmfultothehumanbody,UVCdependsontheglassshellofthehalogenlamp.

3.Fluorescentlamp:adischargelampwithlow-pressuremercuryvaporatthecathode.Theultravioletlightreleasedbythedischargeisconvertedintovisiblelightbythereflectionofthephosphor.Thedouble-spiralortriple-spiraltungstenfilamentisusedonthesurfaceofthefilament.Coatedwithelectronemissionmaterialstoformtheemitter.Theglasstubeisfilledwithamixtureofargon,krypton,andneon,andamalgam,andtheinnerwalloftheglasstubeiscoatedwiththreeprimarycolorphosphors.Itsworkingprinciple:theballastgeneratesapulsevoltagetopreheatthefilament,andtheelectronemissionmaterialonthecathodeisactivatedtogenerateelectrons.Theelectronscollidewiththemercuryatomsinthetubetogenerate253.7nmand185nmultravioletrays.Themainpeakis253.7nm,accountingforabout70%to80%ofthetotalradiantenergy;thesub-peakvalueis185nm,accountingforabout10%ofthetotalradiantenergy.Ultravioletrayspassthroughtheinnerwalloftheglasstubecoatedwithphosphortorefractvisiblelight.Becauseoftheuseofthreeprimarycolorphosphorsandultravioletlightcomponents,thefluorescentlampspectrumhasmultiplesmallspikes,andthereismercuryvaporwithapressureofabout0.8Pa,whichisdischargedundertheactionofanelectricfield,andthevalenceelectronsofmercuryatomsareremovedfromtheoriginalstate.Excitedbecomesanexcitedstate.Atthesametime,itspontaneouslyreturnstothegroundstateinanexcitedstate,convertingvalenceelectronsintoelectromagneticradiationenergy,andradiating353.7nmultravioletrays,andthereareabout10%85nmhigh-frequencyultravioletrays.Thephosphorontheinnerwalloftheglasstubeabsorbs353.7nmultravioletlightandconvertsitintovisiblelight.Sincemostoftheelectricenergyconsumedbyfluorescentlampsisusedtogenerateultravioletrays,theluminousefficiencyoffluorescentlampsismuchhigherthanthatofincandescentlampsandtungstenhalogenlamps,andisamoreenergy-savinglightingsource.Whenthefluorescentlampisworking,thetemperatureofthefilamentisabout1160K,whichismuchlowerthantheworkingtemperatureoftheincandescentlamp,whichis2400～2900K,soitsservicelifeisgreatlyextended,reachingmorethan5000h.Anotherfeatureoffluorescentlampsisthattheyhavegoodcolorrendering,haveideallightingeffectsforcolorfulobjectsandenvironments,andhavelowlightdecay.Therefore,theyarewidelyused.

4.LEDlamp:isasolid-statesemiconductorcomponentthatcanconvertelectricalenergyintovisiblelight,thatis,light-emittingdiodes,whichdirectlyconvertelectricalenergyintolightenergy.ThecorecomponentoftheLEDisasemiconductorchip.Oneendofthechipisattachedtothebracket,oneendisthenegativepole,andtheotherendisthepositivepoleconnectedtothepowersupply.Theentirechipisencapsulatedbyepoxyresin.AsingleLEDlampbeadonlyworksatalowvoltageofabout3Vandalowcurrentofaboutafewmilliamps.Drivecircuit),maketheintegratedmultipleLEDlampbeadsworkunderthemainspower,andtheninstallthelampholder.Theself-ballastedLEDlampreferstoanLEDlampwithalampcapthatcanintegratestableignitioncomponentsintoone,andcaneasilyreplacetraditionalincandescentlamps.CommonlyusedwhiteLEDlightingisafluorescentlightsourceexcitedbyblueLEDs.Exceptforapartoftheheatdissipatedtoelectroniccomponents,mostofthewhitelightenergyofLEDlightingcanbeconvertedintovisiblelight,anditsluminousefficiencycanreach50~200lm/W.Itscharacteristicsaresimplestructure,lowcost,longservicelife,highluminousefficiency,andresistancetobreakage.