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. •• 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. TheTheThe wavelengthwavelengthwavelength isisis relatedrelatedrelated tototo thethethe frequencyfrequencyfrequency fff:::

cc == ffcc == 33 xx 101088 m/sm/s ThoseThose EMEM waveswaves thatthat areare visiblevisible ()(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 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 VisibleVisible SpectrumSpectrum 10 103 14 10 104 13 400400 nmnm  700700 nmnm 10 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 = fc = 3 x 10 m/s 10 1013 c = fc = 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  == 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 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. PhotonsPhotons andand LightLight RaysRays

LightLight maymay bebe thoughtthought ofof asas littlelittle bundlesbundles ofof waveswaves emittedemitted inin discretediscrete packetspackets calledcalled 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


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) 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 (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 lightlight bulbbulb emitsemits aa totaltotal radiantradiant powerpower ofof aboutabout 17501750 lmlm.. ThisThis isis forfor lightlight emittedemitted inin allall directions.directions. TheThe LumenLumen inin PowerPower UnitsUnits RecallingRecalling thatthat luminousluminous fluxflux isis reallyreally radiantradiant powerpower allowsallows usus toto definedefine thethe lumenlumen asas follows:follows:

OneOneOne lumenlumenlumen isisis equalequalequal tototo 1/6801/6801/680 WWW ofofof yellowyellowyellow--- greengreengreen lightlightlight ofofof wavelengthwavelengthwavelength 555555555 nm.nm.nm.

AA disadvantagedisadvantage ofof thisthis Sensitivity curve approachapproach isis thethe needneed toto referrefer toto sensitivitysensitivity curvescurves toto determinedetermine thethe fluxflux forfor differentdifferent colorscolors ofof light.light. Wavelength  LuminousLuminous IntensityIntensity TheThe luminousluminous intensityintensity II forfor aa lightlight sourcesource isis thethe luminousluminous fluxflux perper unitunit solidsolid angle.angle.

Luminous : F F  I  I    Unit is the (cd)

AA sourcesource havinghaving anan intensityintensity ofof oneone candelacandela emitsemits aa fluxflux ofof oneone lumenlumen perper steradiansteradian.. TotalTotal fluxflux forfor IsotropicIsotropic SourceSource

AnAn isotropicisotropic sourcesource emitsemits inin == 44 srsr allall directions;directions; i.e.,i.e., overover aa solidsolid angleangle ofof 44 steradianssteradians..

Thus,Thus, forfor suchsuch F F aa source,source, thethe I  intensityintensity is:is:  4

TotalTotal flux:flux: FF == 44II

TheThe fluxflux confinedconfined toto areaarea AA is:is:  R 3 m FF == II AA ExampleExample 4.4. AA 3030 cdcd spotlightspotlight isis locatedlocated 33 mm aboveabove aa table.table. TheThe beambeam isis focusedfocused onon aa surfacesurface areaarea ofof 0.40.4 mm2.. FindFind thethe intensityintensity ofof thethe beam.beam.

TotalTotal flux:flux: FF == 44II

FFT == 44(30(30 cdcd)) == 377377 lmlm  R 3 m TheThe luminousluminous intensityintensity ofof thethe beambeam dependsdepends onon  A 0.4 m2 22 ;  0.0444 sr BeamBeam Intensity:Intensity: R (3 m) F 754 lm I = 8490 cd I  I = 8490 cd  0.0444 sr IlluminationIllumination ofof aa SurfaceSurface TheTheThe illuminationilluminationillumination EEEofofof aaa surfacesurfacesurface AAAisisis defineddefineddefined asasas thethethe luminousluminousluminous fluxfluxflux perperper unitunitunit areaareaarea (((F/AF/AF/A))) ininin lumenslumenslumens perperper squaresquaresquare metermetermeter whichwhichwhich isisis renamedrenamedrenamed aaa luxluxlux (lx).(lx)(lx)..

An illumination of one An illumination of one lux Illumination, E occursoccurs whenwhen aa fluxflux ofof oneone lumenlumen fallsfalls onon anan areaarea ofof oneone squaresquare  R meter.meter. F E  Unit: lux (lx) A AreaArea AA IlluminationIllumination BasedBased onon IntensityIntensity

TheTheThe illuminationilluminationillumination EEEofofof aaa surfacesurfacesurface isisis directlydirectlydirectly proportionalproportionalproportional tototo thethethe intensityintensityintensity IIIandandand inverselyinverselyinversely proportionalproportionalproportional tototo thethethe squaresquaresquare ofofof thethethe distancedistancedistance RRR...

FF EI; ; FI  A   R IA E  but so that AR2 Area A I Illumination, E  This equation applies for R2 perpendicular . ExampleExample 5.5. AA 400400--cdcd lightlight isis locatedlocated 2.42.4 mm fromfrom aa tabletoptabletop ofof areaarea 1.21.2 mm2.. WhatWhat isis thethe illuminationillumination andand whatwhat fluxflux FF fallsfalls onon thethe table?table? I 400 cd E  R22(2.40 m)  R

Illumination:Illumination: E = 69.4 lx

Now,Now, recallingrecalling thatthat EE == F/AF/A,, wewe findfind FF from:from:

FF == EAEA == (69.4(69.4 lx)(1.20lx)(1.20 mm2)) F = 93.3 lm TheThe InverseInverse SquareSquare RelationshipRelationship

I E/9 E  R2 E/4 9 m2 E 4 m2 1 m2 3 m 2 m 1 m

If the intensity is 36 lx at 1 m, it will be 9 lx at 2 m and only 4 lx at 3 m. SummarySummary

LightLightLight maymaymay bebebe defineddefineddefined asasas electromagneticelectromagneticelectromagnetic radiationradiationradiation thatthatthat isisis capablecapablecapable ofofof affectingaffectingaffecting thethethe sensesensesense ofofof sight.sight.sight.

General Properties of Light: • Rectilinear propagation • Reflection c = fc = 3 x 1088 m/s • Refraction c = fc = 3 x 10 m/s

Red,Red,  Violet,Violet,  700700 nmnm 400400 nmnm SummarySummary (Continued)(Continued)

TheThe formationformation ofof shadows:shadows: penumbrapenumbra

ExtendedExtended sourcesource


LuminousLuminous fluxflux isis thethe portionportion ofof totaltotal radiantradiant powerpower thatthat isis capablecapable ofof affectingaffecting thethe sensesense ofof sight.sight. SummarySummary (Continued)(Continued)

Luminous intensity: R A F I    A Unit is the candela (cd) The  Steradian R2 F E  Unit: lux (lx) TotalTotal flux:flux: FF == 44II A SummarySummary (Cont.)(Cont.)

I Illumination, E  R2 Illumination, E

E/9  R 9 m2 E/4 4 m2 E 1 m2 3 m Area A 2 m Area A 1 m CONCLUSION:CONCLUSION: ChapterChapter 3333 LightLight andand IlluminationIllumination