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Light and Illumination

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Light and Illumination ChapterChapter 3333 -- LightLight andand IlluminationIllumination AAA PowerPointPowerPointPowerPoint PresentationPresentationPresentation bybyby PaulPaulPaul E.E.E. Tippens,Tippens,Tippens, ProfessorProfessorProfessor ofofof PhysicsPhysicsPhysics SouthernSouthernSouthern PolytechnicPolytechnicPolytechnic StateStateState UniversityUniversityUniversity © 2007 Objectives:Objectives: AfterAfter completingcompleting thisthis module,module, youyou shouldshould bebe ableable to:to: •• DefineDefine lightlight,, discussdiscuss itsits properties,properties, andand givegive thethe rangerange ofof wavelengthswavelengths forfor visiblevisible spectrum.spectrum. •• ApplyApply thethe relationshiprelationship betweenbetween frequenciesfrequencies andand wavelengthswavelengths forfor opticaloptical waves.waves. •• DefineDefine andand applyapply thethe conceptsconcepts ofof luminousluminous fluxflux,, luminousluminous intensityintensity,, andand illuminationillumination.. •• SolveSolve problemsproblems similarsimilar toto thosethose presentedpresented inin thisthis module.module. AA BeginningBeginning DefinitionDefinition AllAll objectsobjects areare emittingemitting andand absorbingabsorbing EMEM radiaradia-- tiontion.. ConsiderConsider aa pokerpoker placedplaced inin aa fire.fire. AsAs heatingheating occurs,occurs, thethe 1 emittedemitted EMEM waveswaves havehave 2 higherhigher energyenergy andand 3 eventuallyeventually becomebecome visible.visible. 4 FirstFirst redred .. .. .. thenthen white.white. LightLightLight maymaymay bebebe defineddefineddefined asasas electromagneticelectromagneticelectromagnetic radiationradiationradiation thatthatthat isisis capablecapablecapable ofofof affectingaffectingaffecting thethethe sensesensesense ofofof sight.sight.sight. ElectromagneticElectromagnetic WavesWaves WaveWave Properties:Properties: EE 1.1. WavesWaves traveltravel atat thethe speedspeed ofof lightlight cc.. BB cc 3 x 108 m/s 2.2. PerpendicularPerpendicular electricelectric andand magneticmagnetic fields.fields. ElectricElectric EE 3.3. RequireRequire nono mediummedium MagneticMagnetic BB forfor propagation.propagation. ForFor aa completecomplete reviewreview ofof thethe electromagneticelectromagnetic properties,properties, youyou shouldshould studystudy modulemodule 32C.32C. TheThe WavelengthsWavelengths ofof LightLight TheTheThe electromagneticelectromagneticelectromagnetic spectrumspectrumspectrum spreadsspreadsspreads overoverover aaa tremendoustremendoustremendous rangerangerange ofofof frequenciesfrequenciesfrequencies ororor wavelengths.wavelengths.wavelengths. TheTheThe wavelengthwavelengthwavelength isisis relatedrelatedrelated tototo thethethe frequencyfrequencyfrequency fff::: cc == ffcc == 33 xx 101088 m/sm/s ThoseThose EMEM waveswaves thatthat areare visiblevisible (light)(light) havehave wavewave-- lengthslengths thatthat rangerange fromfrom 0.000040.00004 toto 0.000070.00007 cm.cm. Red,Red, Violet,Violet, 0.000070.00007 cmcm 0.000040.00004 cmcm Frequency wavelength f (Hz) nm) TheThe EMEM SpectrumSpectrum 1024 AA wavelengthwavelength ofof oneone 23 10 10-7 22 10 Gamma rays 10-6 nanometernanometer 11 nmnm is:is: 21 10 10-4 20 10 10-3 -9 19 1 nm = 1 x 10 -9 m 10 10-1 1 nm = 1 x 10 m 18 10 1 17 10 X-rays 10 16 10 102 15 Ultraviolet VisibleVisible SpectrumSpectrum 10 103 14 10 104 13 400400 nmnm 700700 nmnm 10 Infrared rays 105 12 10 106 11 10 107 10 10 Short Radio 108 9 RedRed 700700 nmnm VioletViolet 400400 nmnm 10 waves 109 8 10 1010 7 10 Broadcast Radio 1011 6 10 1012 88 5 Long Radio c = fc = 3 x 10 m/s 10 1013 c = fc = 3 x 10 m/s 104 waves ExampleExample 1.1. LightLight fromfrom aa HeliumHelium--NeonNeon laserlaser hashas aa wavelengthwavelength ofof 632632 nmnm.. WhatWhat isis thethe frequencyfrequency ofof thisthis wave?wave? TheThe HeliumHelium NeonNeon LaserLaser WavelengthWavelength Laser == 632632 nmnm c 3 x 108 m/s cf f 632 x 10-9 m ff == 4.754.75 xx 10101414 Hz Hz RedRed lightlight PropertiesProperties ofof LightLight AnyAnyAny studystudystudy ofofof thethethe naturenaturenature ofofof lightlightlight mustmustmust explainexplainexplain thethethe followingfollowingfollowing observedobservedobserved properties:properties:properties: • Rectilinear propagation: Light travels in straight lines. • Reflection: Light striking a smooth surface turns back into the original medium. • Refraction: Light bends when entering a transparent medium. TheThe NatureNature ofof LightLight PhysicistsPhysicistsPhysicists havehavehave studiedstudiedstudied lightlightlight forforfor centuries,centuries,centuries, findingfindingfinding thatthatthat ititit sometimessometimessometimes behavesbehavesbehaves asasas aaa particleparticleparticle andandand sometimessometimessometimes asasas aaa wave.wave.wave. Actually,Actually,Actually, bothbothboth areareare correct!correct!correct! ReflectionReflection andand rectilinearrectilinear propagationpropagation DispersionDispersion ofof whitewhite (straight(straight lineline path)path) lightlight intointo colors.colors. PhotonsPhotons andand LightLight RaysRays LightLight maymay bebe thoughtthought ofof asas littlelittle bundlesbundles ofof waveswaves emittedemitted inin discretediscrete packetspackets calledcalled photonsphotons.. photonsphotons TheThe wavewave treatmenttreatment usesuses raysrays toto showshow thethe directiondirection ofof advancingadvancing wavewave fronts.fronts. LightLightLight raysraysrays areareare LightLight convenientconvenientconvenient forforfor rayray describingdescribingdescribing howhowhow lightlightlight behaves.behaves.behaves. LightLight RaysRays andand ShadowsShadows AA geometricgeometric analysisanalysis maymay bebe mademade ofof shadowsshadows byby tracingtracing lightlight raysrays fromfrom aa pointpoint lightlight source:source: shadowshadow PointPoint sourcesource screenscreen TheThe dimensionsdimensions ofof thethe shadowshadow cancan bebe foundfound byby usingusing geometrygeometry andand knownknown distances.distances. ExampleExample 2:2: TheThe diameterdiameter ofof thethe ballball isis 44 cmcm andand itit isis locatedlocated 2020 cmcm fromfrom thethe pointpoint lightlight source.source. IfIf thethe screenscreen isis 8080 cmcm fromfrom thethe source,source, whatwhat isis thethe diameterdiameter ofof thethe shadow?shadow? h 4cm TheTheThe ratioratioratio ofofof shadowshadow toto 80cm 20cm shadow to thethethe sourcesourcesource 4 cm h isisis samesamesame asasas thatthatthat ofofof ballballball 20 cm toto source.source. 80 cm to source. Therefore:Therefore:Therefore: (4 cm)(80 cm) h h = 16 cm 20 cm ShadowsShadows ofof ExtendedExtended ObjectsObjects penumbrapenumbra ExtendedExtended sourcesource umbraumbra TheThe•• TheThe umbraumbra umbraumbra isis thethe isis thetheregionregion regionregion wherewhere wherewhere nono lightlightnono lightlight reachesreaches thethe reachesreachesscreen.screen. thethe screen.screen. •• TheThe penumbrapenumbra isis thethe outerouter areaarea wherewhere onlyonly partpart ofof thethe lightlight reachesreaches thethe screen.screen. TheThe SensitivitySensitivity CurveCurve HumanHuman eyeseyes areare notnot SensitivitySensitivity curvecurve equallyequally sensitivesensitive toto 555 nm allall colors.colors. EyesEyes areare mostmost sensisensi-- 400 nm 700 nm tive in the mid-range Sensitivity tive in the mid-range Sensitivity nearnear == 555555 nmnm.. WavelengthWavelength YellowYellowYellow lightlightlight appearsappearsappears brighterbrighterbrighter toto thethe eyeeye thanthan doesdoes redred light.light. 4040 WW 4040 WW to the eye than does red light. LuminousLuminous FluxFlux LuminousLuminous fluxflux isis thethe portionportion ofof totaltotal radiantradiant powerpower thatthat isis capablecapable ofof affectingaffecting thethe sensesense ofof sight.sight. TypicallyTypically onlyonly aboutabout 10%10% ofof thethe powerpower (flux)(flux) emittedemitted fromfrom aa lightlight bulbbulb fallsfalls inin thethe visiblevisible region.region. TheThe unitunit forfor luminousluminous fluxflux isis thethe lumenlumen whichwhich willwill bebe givengiven aa quantitativequantitative definitiondefinition later.later. AA SolidSolid Angle:Angle: SteradiansSteradians WorkingWorking withwith luminousluminous fluxflux requiresrequires thethe useuse ofof aa solidsolid angleangle measuremeasure calledcalled thethe steradiansteradian (sr).(sr). AAA solidsolidsolid angleangleangle ofofof oneoneone steradiansteradian ((11 srsr)) isis steradian (1 sr) is R A subtendedsubtendedsubtended atatat thethethe centercentercenter ofofof aaa spherespheresphere bybyby ananan areaareaarea AAAequalequalequal The A tototo thethethe squaresquaresquare ofofof itsitsits 2 Steradian 2 radiusradiusradius ((( RRR22 ). ).). R ExampleExample 3.3. WhatWhat solidsolid angleangle isis subtendedsubtended atat thethe centercenter ofof aa spheresphere byby anan areaarea ofof 1.61.6 mm2?? TheThe radiusradius ofof thethe spheresphere isis 55 mm.. A R 5 m A R2 1.6 m2 1.60 m2 (5.00 m)2 A The Steradian 2 R == 0.006400.00640 srsr TheThe LumenLumen asas aa UnitUnit ofof FluxFlux OneOne lumenlumen (lm)(lm) isis thethe luminousluminous fluxflux emittedemitted fromfrom aa 1/601/60 cmcm2 openingopening inin aa standardstandard sourcesource andand includedincluded inin aa solidsolid angleangle ofof oneone steradiansteradian (1(1 srsr).). InIn practice,practice, sourcessources ofof lightlight areare usuallyusually ratedrated byby comparisoncomparison toto aa commerciallycommercially preparedprepared standardstandard lightlight source.source. AA typicaltypical 100100--WW incandescentincandescent
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