led照明中英文对照外文翻译文献.docx
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led照明中英文对照外文翻译文献.docx
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led照明中英文对照外文翻译文献
(文档含英文原文和中文翻译)
中英文资料外文翻译文献
RenewableandSustainableEnergyReviews
High-brightnessLEDs—Energyefficientlightingsourcesandtheirpotentialinindoorplantcultivation
ABSTRACT
Therapiddevelopmentofoptoelectronictechnologysincemid-1980hassignificantlyenhancedthebrightnessandefficiencyoflight-emittingdiodes(LEDs).LEDshavelongbeenproposedasaprimarylightsourceforspace-basedplantresearchchamberorbioregenerativelifesupportsystems.TheraisingcostofenergyalsomakestheuseofLEDsincommercialcropcultureimminent.Withtheirenergyefficiency,LEDshaveopenednewperspectivesforoptimizingtheenergyconversionandthenutrientsupplybothonandoffEarth.ThepotentialsofLEDasaneffectivelightsourceforindooragriculturalproductionhavebeenexploredtoagreatextent.TherearemanyresearchesthatuseLEDstosupportplantgrowthincontrolledenvironmentssuchasplanttissuecultureroomandgrowthchamber.ThispaperprovidesabriefdevelopmenthistoryofLEDsandabroadbasereviewonLEDapplicationsinindoorplantcultivationsince1990.
Contents
1.Introduction
2.LEDdevelopment.
3.Colorratiosandphotosynthesis
4.LEDsandindoorplantcultivation.
4.1.Planttissuecultureandgrowth
4.2.Spaceagriculture8
4.3.Algaculture
4.4.Plantdiseasereduction
5.Intermittentandphotoperiodlightingandenergysaving
6.Conclusion
1.Introduction
Withimpactsofclimatechange,issuessuchasmorefrequentandseriousdroughts,floods,andstormsaswellaspestanddiseasesarebecomingmoreseriousthreatstoagriculture.Thesethreatsalongwithshortageoffoodsupplymakepeopleturntoindoorandurbanfarming(suchasverticalfarming)forhelp.Withproperlighting,indooragricultureeliminatesweather-relatedcropfailuresduetodroughtsandfloodstoprovideyear-roundcropproduction,whichassistinsupplyingfoodincitieswithsurgingpopulationsandinareasofsevereenvironmentalconditions.
Theuseoflight-emittingdiodesmarksgreatadvancementsoverexistingindooragriculturallighting.LEDsallowthecontrolofspectralcompositionandtheadjustmentoflightintensitytosimulatethechangesofsunlightintensityduringtheday.Theyhavetheabilitytoproducehighlightlevelswithlowradiantheatoutputandmaintainusefullightoutputforyears.LEDsdonotcontainelectrodesandthusdonotburnoutlikeincandescentorfluorescentbulbsthatmustbeperiodicallyreplaced.Nottomentionthatincandescentandfluorescentlampsconsumealotofelectricalpowerwhilegeneratingheat,whichmustbedispelledfromclosedenvironmentssuchasspaceshipsandspacestations.
2.LEDdevelopment
LEDisauniquetypeofsemiconductordiode.Itconsistsofachipofsemiconductormaterialdopedwithimpuritiestocreateap–njunction.Currentflowseasilyfromthep-side(anode),tothen-side(cathode),butnotinthereversedirection.
Electronsandholesflowintothejunctionfromelectrodeswithdifferentvoltages.Whenanelectronmeetsahole,itfallsintoalowerenergylevel,andreleasesenergyintheformofaphoton.Thecolor(wavelength)ofthelightemitteddependsonthebandgapenergyofthematerialsformingthep–njunction.ThematerialsusedforanLEDhaveadirectbandgapwithenergiescorrespondingtonear-infrared,visibleornear-ultravioletlight.
ThekeystructureofanLEDconsistsofthedie(orlight-emittingsemiconductormaterial),aleadframewherethedieisplaced,andtheencapsulationwhichprotectsthedie(Fig.1).
Fig.1
LEDdevelopmentbeganwithinfraredandreddevicesmadewithgalliumarsenide.Advancesinmaterialssciencehavemadepossibletheproductionofdeviceswithever-shorterwavelengths,producinglightinavarietyofcolors.J.Margolinreportedthatthefirstknownlight-emittingsolidstatediodewasmadein1907byH.J.Round.NopracticaluseofRound’sdiodewasmadeforseveraldecadesuntiltheinventionofthefirstpracticalLEDbyNickHolonyak,Jrin1962.HisLEDsbecamecommerciallyavailableinlate1960s.TheseGaAsPLEDscombinethreeprimaryelements:
gallium,arsenicandphosphorustoprovidea655nmredlightwithbrightnesslevelsofapproximately1–10mcdat20mA.Astheluminousintensitywaslow,theseLEDswereonlyusedinafewapplications,primarilyasindicators.FollowingGaAsP,GaP(galliumphosphide)redLEDsweredeveloped.Thesedevicesexhibitveryhighquantumefficienciesatlowcurrents.AsLEDtechnologyprogressedthroughthe1970s,additionalcolorsandwavelengthsbecameavailable.ThemostcommonmaterialswereGaPgreenandred,GaAsPorange,andhighefficiencyredandGaAsPyellow.Thetrendtowardsmorepracticalapplications(suchasincalculators,digitalwatches,andtestequipment)alsobegantodevelop.AstheLEDmaterialstechnologybecamemoreadvanced,thelightoutputwasincreased,andLEDsbecamebrightenoughtobeusedforillumination.
In1980sanewmaterial,GaAlAs(galliumaluminumarsenide)wasdevelopedfollowedbyarapidgrowthintheuseofLEDs.GaAlAstechnologyprovidessuperiorperformanceoverpreviouslyavailableLEDs.Thevoltagerequirementislower,whichresultsinatotalpowersavings.LEDscouldbeeasilypulsedormultiplexedandthusaresuitableforvariablemessageandoutdoorsigns.Alongthisdevelopmentperiod,LEDswerealsodesignedintobarcodescanners,fiberopticdatatransmissionsystems,andmedicalequipment.Duringthistime,theimprovementsincrystalgrowthandopticsdesignallowyellow,greenandorangeLEDsonlyaminorimprovementinbrightnessandefficiency.Thebasicstructureofthematerialremainedrelativelyunchanged.
Aslaserdiodeswithoutputinthevisiblespectrumstartedtocommercializeinlate1980s,LEDdesignersusedsimilartechniquestoproducehigh-brightnessandhighreliabilityLEDs.ThisledtothedevelopmentofInGaAlP(indiumgalliumaluminumphosphide)visiblelightLEDs.ViaadjustingtheenergybandgapInGaAlPmaterialcanhavedifferentcoloroutput.Thus,green,yellow,orangeandredLEDscouldallbeproducedusingthesamebasictechnology.Also,lightoutputdegradationofInGaAlPmaterialissignificantlyimproved.
ShujiNakamuraatNichiaChemicalIndustriesofJapanintroducedblueLEDsin1993.BlueLEDshavealwaysbeendifficulttomanufacturebecauseoftheirhighphotonenergies(>2.5eV)andrelativelyloweyesensitivity.Also,thetechnologytofabricatetheseLEDsisverydifferentandlessadvancedthanstandardLEDmaterials.Butblueisoneoftheprimarycolors(theothertwobeingredandgreen).Properlycombiningthered,green,andbluelightisessentialtoproducewhiteandfull-color.Thisprocessrequiressophisticatedsoftwareandhardwaredesigntoimplement.Inaddition,thebrightnesslevelislowandtheoveralllightoutputofeachRGBdiebeinguseddegradesatadifferentrateresultinginaneventualcolorunbalance.TheblueLEDsavailabletodayconsistofGaN(galliumnitride)andSiC(siliconcarbide)construction.TheblueLEDthatbecomesavailableinproductionquantitieshasresultinanentiregenerationofnewapplicationsthatincludetelecommunicationsproducts,automotiveapplications,trafficcontroldevices,andfull-colormessageboards.EvenLEDTVscansoonbecomecommerciallyavailable.
Comparetoincandescentlight’s1000-handfluorescentlight’s8000-hlifespan,LEDshaveaverysignificantlylongerlifeof100,000h.Inadditiontotheirlonglife,LEDshavemanyadvantagesoverconventionallightsource.Theseadvantagesincludesmallsize,specificwavelength,lowthermaloutput,adjustablelightintensityandquality,aswellashighphotoelectricconversionefficiency.SuchadvantagesmakeLEDsperfectforsupportingplantgrowthincontrolledenvironmentsuchasplanttissuecultureroomandgrowthchamber.Table1isalistofsomecommontypesofLEDsascompiledfrom.
Table1
SomecommontypesofLEDs.
Peakwavelength(nm)
Color
MaterialandstructureofLEDs
Substrate
730
Far-red
GaAs
GaP
700
Red
GaP:
Zn-O
GaP
660
Red
GaAl0.35As
GaAs
650
Red
GaAs0.6P
GaAs
630
Orange–red
GaAs0.35P0.65:
N
GaP
610
Orange
GaAs0.25P0.75:
N
GaP
590
Yellow
GaAs0.15P0.85:
N
GaP
585
Yellow
GaAs0.14P0.86:
N
GaAs
565
Green
GaP:
N
GaP
450
Blue
GaN/SiC
–
3.Colorratiosandphotosynthesis
Thechlorophyllmoleculesinplantsinitiatephotosynthesisbycapturinglightenergyandconvertingitintochemicalenergytohelptransformingwaterandcarbondioxideintotheprimarynutrientforlivingbeings.Thegeneralizedequationforthephotosyntheticprocessisgivenas:
CO2+H2O—light—>(CH2O)+O2
where(CH2O)isthechemicalenergybuildingblockforthesynthesisofplantcomponents.
Chlorophyllmoleculesabsorbblueandredwavelengthsmostefficiently.Thegreenandyellowwavelengthsarereflectedortransmittedandthusarenotasimportantinthephotosynthetic
process.Thatmeanslimittheamountofcolorgiventotheplantsandstillhavethemgrowaswellaswithwhitelight.So,thereisnoneedtodevoteenergytogreenlightwhenenergycostsarea
concern,whichisusuallythecaseinspacetravel.
TheLEDsenableresearcherstoeliminateotherwavelengthsfoundwithinnormalwhitelight,thusreducingtheamountofenergyrequiredtopowertheplantgrowthlamps.Theplantsgrownormallyandtastethesameasthoseraisedinwhitelight.
Redandbluelightbestdrivephotosyntheticmetabolism.Theselightqualitiesareparticularlyefficientinimprovingthedevelopmentalcharacteristicsassociatedwithautotrophicgrowthhabits.Nevertheless,photosyntheticallyinefficientlightqualitiesalsoconveyimportantenvironmentalinformationtoadevelopingpla
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