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Lub teeb-emitting diode (LED), emitting lub teeb thaum electrically them ua electroluminescence

Lub teeb-emitting diode (LED), emitting lub teeb thaum electrically them ua electroluminescence

Apr 21, 2017

Lub teeb-emitting diode

Lub teeb-emitting diode
RBG-LED.jpg Xiav, ntsuab, thiab liab LEDs nyob rau hauv 5 hli diffused cov ntaub ntawv
Ua hauj lwm hauv paus ntsiab lus Electroluminescence
yees H._J._Round (1907) [1]
Oleg Losev (1927) [2]
James R. Biard (1961) [3]
Nick Holonyak (1962) [4]
thawj ntau lawm Lub kaum hli ntuj 1962
pin configuration Anode thiab cathode
Hauv lub cim
LED symbol.svg


Qhov ntawm ib tug pa LED. Lub tiaj hauv qab chaw ntawm lub thaiv thiab ncej kos rau hauv lub epoxy ua raws li anchors, los mus tiv thaiv lub conductors ntawm raug ntiag rub tawm ntawm cov neeg kho tshuab lim los yog kev co.











Niaj hnub nimno LED retrofit nrog E27 hau ntswj nyob rau hauv lub hauv paus


Ib tug teeb-zoo li tus niaj hnub retrofit LED teeb nrog txhuas tshav kub tog , ib lub teeb diffusing dome thiab E27 hau ntswj puag, siv ib tug built-in fais fab mov ua hauj lwm rau mains voltage




Kaw cov duab ntawm ib tug saum npoo roob LED





Ib lub teeb-emitting diode (LED) yog ib tug ob lead semiconductor teeb qhov chaw . Nws yog ib tug p-n hlws ris diode , uas emits lub teeb thaum tshuab txais. [5] Thaum ib tug haum voltage yog thov mus rau lub ua, electrons yuav tau recombine nrog electron qhov nyob rau hauv lub ntaus ntawv, tso lub zog nyob rau hauv daim ntawv ntawm cov photons . Cov nyhuv no yog hu ua electroluminescence , thiab cov xim ntawm lub teeb (coj mus rau lub zog ntawm cov photon) yog txiav txim los ntawm lub zog band kis ntawm lub semiconductor. LEDs yog feem ntau me me (tsawg tshaj li 1 hli 2) thiab kev kho qhov muag Cheebtsam yuav siv tau los yog cov tawg qauv . [6]

Hnyuj hnyo li cov tswv yim siv hluav taws xob Cheebtsam nyob rau hauv 1962, [7] cov earliest LEDs tawm txim liab tsis muaj-siv infrared teeb. Infrared LEDs tseem nquag siv raws li kis ntsiab nyob rau hauv tej thaj chaw deb tswj circuits, xws li cov neeg nyob rau hauv tej thaj chaw deb ntawm lwm yam uas rau ib tug ntau yam ntawm cov neeg siv electronics. Tus thawj pom teeb LEDs kuj ntawm tsis muaj kev siv thiab tsuas yog siv rau liab. Niaj hnub nimno LEDs yog muaj nyob thoob plaws hauv pom , ultraviolet , thiab infrared wavelengths, nrog heev brightness.

Early LEDs muaj feem ntau siv raws li qhia teeb rau hauv hluav taws xob pab kiag li lawm, hloov me me incandescent qhov muag teev. Lawv sai sai fej mus rau hauv numeric readouts nyob rau hauv daim ntawv ntawm xya-ya qhia thiab tau feem ntau pom nyob rau hauv cov ntoos. Tsis ntev los no uas nyob rau hauv LEDs tso cai rau lawv yuav tsum tau siv nyob rau hauv ib puag ncig thiab ua hauj lwm teeb pom kev zoo. LEDs tau tso cai tshiab qhia thiab sensors yuav tsum tau tsim, thaum lawv cov qib high switching nqi kuj siv nyob rau hauv advanced kev sib txuas lus tshuab.

LEDs muaj ntau yam zoo tshaj incandescent teeb qhov chaw xws li qis zog noj, ntev lub neej, paub lub cev robustness, me me luaj li, thiab sai switching. Lub teeb-emitting diodes yog tam sim no siv nyob rau hauv daim ntaub ntawv raws li muaj ntau haiv neeg raws li aviation teeb pom kev zoo , tsheb headlamps , advertising, kev teeb pom kev zoo , tsheb Pib ntsais koj teeb , lub koob yees duab flashes, thiab tau taws teeb wallpaper. Raws li ntawm 2017, LED teeb lub tsev chav teeb pom kev zoo muaj raws li pheej yig los yog pheej yig dua tshaj compact fluorescent teeb qhov chaw ntawm piv tso zis. [8] Lawv yog cov tseem ho ntau zog npaum thiab, arguably, muaj tsawg dua tej kev txhawj xeeb txuas rau lawv pov tseg. [9] [10]


txheem

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Keeb kwm [ edit ]

Discoveries thiab thaum ntxov pab kiag li lawm [ edit ]

Ntsuab electroluminescence los ntawm ib tug taw tes hu rau ib tug siv lead ua los ntawm sic recreates Round 's thawj xyaum ua tej yam los ntawm 1907.

Electroluminescence raws li ib tug tshwm sim tau raug nrhiav tau nyob rau hauv 1907 los ntawm cov British experimenter HJ Round ntawm Marconi no-piv , siv ib tug siv lead ua los ntawm silicon carbide thiab ib tug cat's-hwj txwv ntes . [11] [12] Lavxias teb sab inventor Oleg Losev qhia creation ntawm cov thawj LED nyob rau hauv 1927. [13] Nws kev tshawb fawb tau faib nyob rau hauv Soviet, German thiab British scientific txhua hnub, tab sis tsis muaj tswv yim siv raug ua los ntawm lub foundations rau ob peb decades. [14] [15] Kurt Lehovec , Carl Accardo, thiab Edward Jamgochian piav txog tej teeb thawj-emitting diodes nyob rau hauv 1951 kev siv ib qho apparatus ua hauj lwm sic muaju nrog rau ib tug tam sim no qhov chaw ntawm roj teeb los yog mem tes generator thiab nrog ib tug sib piv mus rau ib tug variant, ntshiab, siv lead ua nyob rau hauv 1953. [16] [17]

Rubin Braunstein [18] ntawm cov xov tooj cua Corporation of America qhia rau infrared emission ntawm gallium arsenide (GaAs) thiab lwm yam semiconductor alloys nyob rau hauv 1955. [19] Braunstein cai infrared emission generated los ntawm tej yam yooj yim diode lug siv gallium antimonide (GaSb), GaAs, indium phosphide (InP), thiab silicon-germanium (SiGe) alloys ntawm chav tsev kub thiab ntawm 77 Kelvin.

Nyob rau hauv 1957, Braunstein ntxiv pom hais tias lub rudimentary pab kiag li lawm yuav tau siv rau tsis yog-xov tooj cua kev sib txuas lus nyob rau ib tug luv luv deb. Raws li muab sau los ntawm Kroemer [20] Braunstein "... tau teem ib tug yooj yim kho qhov muag sib txuas lus link: Music tawm los ntawm ib cov ntaub ntawv uas ua ntawv tau siv ntawm haum electronics rau modulate lub rau pem hauv ntej tam sim no ntawm ib tug GaAs diode. Cov tawm txim liab teeb twb ntes tau los ntawm ib tug PBS diode ib co deb deb. qhov no teeb liab twb noj mus rau hauv ib qho suab amplifier thiab ua si rov qab los ntawm ib tug loudspeaker. intercepting lub beam nres lub suab paj nruag. Peb muaj ib tug yawm deal ntawm kev lom zem ua si nrog no teeb. " Qhov no teeb presaged siv ntawm LEDs rau kho qhov muag sib txuas lus ntaub ntawv sau npe.

Ib tug Texas seev SNX-100 GaAs LED muaj nyob rau hauv ib tug TO-18 transistor hlau cov ntaub ntawv.

Nyob rau hauv lub Cuaj Hli Ntuj 1961, thaum ua hauj lwm ntawm Texas seev nyob rau hauv Dallas , Texas , James R. Biard thiab Gary Pittman sab nyob ze-infrared (900 nm) lub teeb emission los ntawm ib tug qhov diode lawv tau lub tsev nyob rau ib lub GaAs substrate. [7] By Lub kaum hli ntuj 1961, lawv tau pom hais tias nws npaum lub teeb emission thiab teeb liab coupling ntawm ib tug GaAs pn hlws ris teeb emitter thiab ib tug electrically-cais semiconductor photodetector. [21] Nyob rau lub yim hli ntuj 8, 1962, Biard thiab Pittman tsum yog ib tug patent hu ua "semiconductor Radiant Diode" raws li lawv tshawb pom, uas piav ib zinc diffused p-n hlws ris LED nrog ib tug spaced cathode hu los pub rau npaum emission ntawm infrared teeb nyob rau hauv pem hauv ntej kev tsis ncaj ncees . Tom qab tsim kom cov kev tseem ceeb tshaj ntawm lawv cov chaw ua hauj lwm raws li engineering phau ntawv sau predating submissions los ntawm GE no-piv, RCA tshawb fawb no-piv, IBM tshawb fawb no-piv, Tswb no-piv , thiab Lincoln Lab ntawm MIT , lub U.S. patent chaw ua hauj lwm muab ob tug inventors lub patent rau lub GaAs infrared (IR ) lub teeb-emitting diode (US Patent US3293513 ), tus thawj tswv yim LED. [7] Tam sim ntawd tom qab ua ntaub ntawv foob tus patent, Texas seev (TI) pib ib qhov project los tsim infrared diodes. Nyob rau hauv Lub kaum hli ntuj 1962, TI tshaj tawm cov thawj coj mus muag LED product (lub SNX-100), uas ua hauj lwm ib tug dawb huv GaAs siv lead ua rau emit ib tug 890 nm teeb tso zis. [7] Nyob rau hauv Lub kaum hli ntuj 1963, TI tshaj tawm cov thawj coj mus muag hemispherical LED, lub SNX-110. [22]

Tus thawj pom-spectrum (liab) LED yog tsim nyob rau hauv 1962 los ntawm Nick Holonyak, Jr. thaum ua hauj lwm ntawm General Electric . Holonyak thawj qhia nws LED nyob rau hauv cov phau ntawv journal Applied Physics ntawv rau hlis ntuj nqeg 1, 1962. [23] [24] M. George Craford , [25] ib tug qub kawm tiav me nyuam kawm ntawv ntawm Holonyak, yees ua lub thawj daj LED thiab zoo dua lub brightness ntawm liab thiab liab-txiv kab ntxwv LEDs los ntawm ib yam ntawm kaum nyob rau hauv 1972. [26] nyob rau hauv 1976, TP Pearsall tsim thawj high-brightness, high-efficiency LEDs rau kho qhov muag fiber telecommunications los ntawm inventing tshiab semiconductor ntaub ntawv uas nruj heev heev rau kho qhov muag fiber kis tau tus mob wavelengths. [27]

Initial coj mus muag kev loj hlob [ edit ]

Tus thawj coj mus muag LEDs tau ntau siv raws li replacements rau incandescent thiab neon qhia teeb, thiab nyob rau hauv xya-ya qhia , [28] thawj nyob rau hauv kim cov khoom xws li kuaj thiab electronics khoom mus kuaj, ces tom qab nyob rau hauv xws cov khoom siv raws li cov TV, cov radios, xov tooj, cov cav laij leb, raws li zoo raws li nyob ua si (saib daim ntawv teev cov teeb liab siv ). Kom txog rau thaum 1968, pom thiab infrared LEDs twb tsis tshua muaj kim, nyob rau hauv qhov kev txiav txim ntawm US $ 200 ib chav tsev, thiab thiaj li muaj me ntsis kev siv tswv yim. [29] Tus Monsanto tuam txhab yog thawj lub koom haum rau loj-tsim pom LEDs, siv gallium arsenide phosphide (GaAsP) nyob rau hauv 1968 yuav tsim liab LEDs haum rau indicators. [29] Hewlett Packard (HP) tswvcuab LEDs nyob rau hauv 1968, chiv siv GaAsP nkag los Monsanto. Cov liab LEDs twb kaj txaus tsuas yog rau cov kev siv raws li indicators, As, raws li lub teeb tso zis twb tsis txaus los taws ib cheeb tsam. Readouts nyob rau hauv cov cav laij leb thiaj li me me uas yas lo ntsiab muag tau ua dua txhua tug lej kom lawv sau zoo. Tom qab ntawd, lwm yam xim ua muaj dav thiab tshwm sim nyob rau hauv cov khoom siv thiab cov khoom siv. Nyob rau hauv lub xyoo 1970 muag vam meej LED li ntawm tsawg tshaj li tsib xees txhua tau ua los ntawm Fairchild Optoelectronics. Cov pab kiag li lawm ua hauj lwm compound semiconductor chips kev qhia nrog lub planar txheej txheem yees los ntawm Dr. Jean Hoerni ntawm Fairchild semiconductor . [30] [31] Lub ua ke ntawm planar ua rau nti fabrication thiab txoj kev ntim txoj kev enabled lub pab neeg ntawm Fairchild coj los optoelectronics pioneer Thomas Brandt mus cuag cov uas yuav tsum tau them nqi txo. [32] Cov kev tseem yuav siv los ntawm LED producers. [33]

LED zaub ntawm ib tug TI-30 scientific calculator (ca. 1978), uas siv yas ntsiab muag kom pom zauv loj

Feem ntau cov LEDs tau ua nyob rau hauv lub heev 5 hli T1¾ thiab 3 hli T1 tej pob khoom, tab sis nrog nce tso zis ntau zog, nws tau zus nce tsim nyog los tshaj thaum tshav kub kub kom muaj kev ntseeg, [34] li ntau pob khoom tau siv tau rau npaum tshav kub dissipation . Tej pob khoom rau lub xeev-of-the-art high-power LEDs dais me ntsis resemblance mus rau thaum ntxov LEDs.

Blue LED [ edit ]

Blue LEDs twb xub tsim los ntawm Herbert Paul Maruska ntawm RCA nyob rau hauv 1972 siv gallium nitride (GaN) rau ib tug sapphire substrate. [35] [36] sic-hom twb xub muag muag nyob rau hauv lub tebchaws United States los ntawm Cree nyob rau hauv 1989. [37] Txawm li cas los, tej nuj nqis ntawm cov thawj xiav LEDs heev kaj.

Tus thawj high-brightness xiav LED twb pom hais tias los ntawm Shuji Nakamura ntawm Nichia Corporation nyob rau hauv 1994 thiab yog raws InGaN . [38] [39] Nyob rau hauv parallel, Isamu Akasaki thiab Hiroshi Amano nyob rau hauv Nagoya tau ua hauj lwm nyob rau hauv tsim lub tseem ceeb GaN nucleation rau sapphire substrates thiab ua tus qauv qhia ntawm p-hom doping ntawm GaN. Nakamura, Akasaki, thiab Amano twb muab tsub lub 2014 Nobel nqi zog nyob rau hauv physics rau lawv ua hauj lwm. [40] Nyob rau hauv 1995, Alberto Barbieri nyob rau Cardiff University Laboratory (GB) tshawb xyuas cov efficiency thiab kev cia siab ntawm high-brightness LEDs thiab pom hais tias nws ib tug "tshab hu rau" LED siv indium tin oxide (Ito) rau (AlGaInP / GaAs).

Nyob rau hauv 2001 [41] thiab 2002, [42] dab rau loj hlob gallium nitride (GaN) LEDs rau silicon tau ntse pom. Nyob rau hauv Lub ib hlis ntuj 2012, Osram pom high-power InGaN LEDs zus rau silicon substrates muag. [43]

Dawb LEDs thiab lub illumination txhob [ edit ]

Lub attainment ntawm high efficiency nyob rau hauv xiav LEDs sai sai raws li los ntawm txoj kev loj hlob ntawm cov thawj dawb LED . Nyob rau hauv no ntaus ntawv ib tug Y
3 Al
5 Au cov neeg
12: Ce (lub npe hu ua " yag ") phosphor txheej rau lub emitter absorbs ib co ntawm cov kob xiav emission thiab ua daj lub teeb los ntawm fluorescence . Lub ua ke ntawm uas daj nrog seem uas xiav lub teeb tshwm dawb rau lub qhov muag. Txawm li cas los, siv ntau phosphors (fluorescent ntaub ntawv) nws kuj los ua tau rau es tsis txhob tsim ntsuab thiab lub teeb liab los ntawm fluorescence. Cov uas ua sib tov ntawm liab, ntsuab thiab xiav yog tsis tsuas ntaus nqi los ntawm cov tib neeg raws li lub teeb dawb, tiam sis yog superior rau illumination nyob rau hauv cov nqe lus ntawm cov xim rendering , whereas ib tug yuav tsis txaus siab rau cov xim ntawm liab los yog ntsuab khoom illuminated los ntawm lub daj (thiab tshuav xiav) wavelengths los ntawm lub yag phosphor.

Lus piv txwv txog Haitz txoj cai , uas qhia txhim kho nyob rau hauv lub teeb tso zis ib LED lub sij hawm, nrog ib tug logarithmic scale nyob rau ntsug axis

Tus thawj dawb LEDs twb kim thiab inefficient. Txawm li cas los, cov teeb tso zis ntawm LEDs muaj ntau zog exponentially , nrog ib tug doubling tshwm sim kwv yees li txhua txhua 36 lub hlis txij thaum lub 1960 (zoo li Moore txoj cai ). Qhov no sib yog feem ntau ntaus nqi mus rau thaum uas tig mus kev loj hlob ntawm lwm yam semiconductor technologies thiab kev kho nyob rau hauv optics [ citation ntxiv ] thiab ntaub ntawv science thiab tau raug hu ua Haitz txoj cai tom qab Dr. Roland Haitz. [44]

Lub teeb cov zis thiab efficiency ntawm xiav thiab nyob ze-ultraviolet LEDs sawv raws li tus nqi ntawm txhim khu kev qha pab kiag li lawm poob: qhov no coj mus rau qhov kev siv ntawm (kuj) high-hwj chim dawb-teeb LEDs rau lub hom phiaj ntawm illumination uas yog hloov incandescent thiab Fluorescent teeb pom kev zoo. [45] [46]

Seb dawb LEDs tau pom hais tias nws tsim tshaj 300 lumens ib watt ntawm hluav taws xob; ib co yuav kav mus txog rau 100,000 teev. [47] Piv rau incandescent qhov muag, qhov no tsis yog tsuas yog ib tug lossis loj nce nyob rau hauv hluav taws xob efficiency tab sis - thaum lub sij hawm - ib tug zoo sib xws los txo nqi ib teev. [48]

Ua hauj lwm hauv paus ntsiab lus [ edit ]

Lub puab workings ntawm ib tug LED, uas qhia Circuit Court (saum) thiab band daim duab (hauv qab)

Ib tug PN hlws ris yuav hloov siab los ntseeg absorbed lub teeb zog rau hauv ib lub proportional hluav taws xob tam sim no. Cov tib cov txheej txheem yog ntxeev ntawm no (piv txwv li lub PN hlws ris emits lub teeb thaum hluav taws xob lub zog yog thov mus rau nws). Qhov no tshwm sim feem ntau yog hu ua electroluminescence , uas yuav muab txhais li lub emission ntawm lub teeb los ntawm ib tug semi-neeg xyuas pib nyob rau hauv tus ntawm ib tug hluav taws xob field . Tus nqi muaj recombine nyob rau hauv ib tug rau pem hauv ntej-biased PN hlws ris li cov electrons hla los ntawm lub N-cheeb tsam thiab recombine nrog lub qhov uas twb muaj lawm nyob rau hauv lub P-cheeb tsam. Dawb electrons yog nyob rau hauv lub conduction qhab ntawm lub zog ntau ntau, thaum qhov yog nyob rau hauv lub valence zog band . Yog li lub zog ntawm lub qhov yuav tsum tau tsawg dua lub zog theem ntawm lub electrons. Ib txhia feem ntawm lub zog yuav tsum tau dissipated nyob rau hauv thiaj li yuav recombine lub electrons thiab lub qhov. No lub zog yog tawm txim liab nyob rau hauv daim ntawv ntawm tshav kub thiab lub teeb.

Lub electrons dissipate zog nyob rau hauv daim ntawv ntawm tshav kub rau silicon thiab germanium diodes tab sis nyob rau hauv gallium arsenide phosphide (GaAsP) thiab gallium phosphide (GAP) semiconductors, lub electrons dissipate zog los ntawm emitting photons . Yog hais tias lub semiconductor yog translucent, lub hlws ris ua lub chaw ntawm lub teeb raws li nws yog tawm txim liab, yog li ua ib lub teeb-emitting diode, tab sis thaum lub hlws ris yog rov qab ntxub tsis muaj lub teeb yuav tsum ua los ntawm cov LED thiab, yog tias lub peev xwm yog zoo txaus, tus ntaus ntawv yuav yuav puas ntsoog.

Technology [ edit ]

IV daim duab rau ib tug diode . Ib tug LED yuav pib emit teeb thaum ntau tshaj li 2 los yog 3 volts yog thov mus rau nws. Cov rov qab tsis ncaj ncees cheeb tsam siv ib tug txawv ntsug teev los ntawm lub rau pem hauv ntej kev tsis ncaj ncees cheeb tsam, nyob rau hauv thiaj li yuav qhia tau tias tus to tam sim no yog ze li ntawm qhov uas voltage kom txog thaum lub neej puas tshwm sim. Nyob rau hauv pem hauv ntej kev tsis ncaj ncees, qhov tam sim no yog me me tab sis tsub kom exponentially nrog voltage.

Physics [ edit ]

Lub LED muaj ib tug nti ntawm semiconducting khoom doped nrog impurities los ua ib tug pn hlws ris . Raws li nyob rau hauv lwm yam diodes, tam sim no ntws yooj yim los ntawm cov p-sab, los yog anode , mus rau lub n-sab, los yog cathode, tab sis tsis nyob rau hauv lub rov qab cov kev taw qhia. Charge-carriers- electrons thiab qhov -flow rau hauv lub hlws ris los ntawm electrodes nrog txawv voltages. Thaum ib tug electron raws li ib tug qhov, nws ntog mus rau hauv ib tug qis zog thiab tawm zog nyob rau hauv daim ntawv ntawm ib tug photon .

Cov wavelength ntawm lub teeb tawm txim liab, thiab yog li nws cov xim, nyob rau hauv lub band kis zog ntawm cov ntaub ntawv txoj kev ua pn hlws ris. Nyob rau hauv pob zeb ntais los yog germanium diodes, lub electrons thiab qhov feem ntau recombine los ntawm ib tug uas tsis yog-radiative hloov, uas ua tsis kho qhov muag emission, vim hais tias cov no yog cov indirect band kis cov ntaub ntawv. Cov ntaub ntawv siv rau kev LED muaj ib tug ncaj qha band kis nrog energies coj mus ze-infrared, pom, los yog nyob ze-ultraviolet lub teeb.

LED txoj kev loj hlob pib nrog infrared thiab liab pab kiag li lawm ua nrog gallium arsenide . Kev kho tshiab hauv ntaub ntawv science tau enabled siab pab kiag li lawm nrog puas tau-luv wavelengths, emitting teeb nyob rau hauv ib tug ntau yam ntawm cov xim.

LEDs no feem ntau yog ua nyob rau hauv ib tug n-hom substrate, nrog ib tug electrode txuas mus rau lub p-hom txheej tso rau nws saum npoo. P-hom substrates, thaum tsis tshua muaj heev, tshwm sim zoo li. Muaj ntau coj mus muag LEDs, tshwj xeeb tshaj yog GaN / InGaN, kuj siv tau sapphire substrate.

Refractive index [ edit ]

Idealized piv txwv ntawm lub teeb emission cones nyob rau hauv ib tug yooj yim square semiconductor, rau ib tug taw tes-qhov chaw emission tsam. Lub sab laug kev yog rau ib tug translucent wafer, thaum lub sij hawm txoj kev qhia tau hais tias ib nrab-cones tsim thaum lub hauv qab txheej yog opaque. Lub teeb yog ua tau tawm txim liab Attendance nyob rau hauv tag nrho cov lus qhia los ntawm tus taw tes-qhov twg los, tab sis tsuas khiav perpendicular mus rau lub semiconductor nto thiab ib co degrees rau sab, uas yog taw qhia los ntawm cov khob hliav qab daim. Thaum lub tseem ceeb heev lub yog ua zoo tshaj, photons yog thaws rov los ntxiv hauv lawv. Lub chaw ntawm lub cones sawv cev rau lub trapped teeb lub zog lub sij hawm raws li thaum tshav kub kub. [49] Feem ntau cov ntaub ntawv siv rau LED ntau lawm muaj siab heev refractive indices . Qhov no txhais tau tias ntau npaum li cas ntawm lub teeb yuav tsum reflected rov qab mus rau hauv cov khoom nyob rau hauv cov ntaub ntawv / cua nto interface. Yog li, lub teeb extraction nyob rau hauv LEDs yog ib qho tseem ceeb nam ntawm LED ntau lawm, yuav raug npaum li cas cov kev tshawb fawb thiab kev loj hlob. Lub teeb emission cones ntawm ib tug tiag tiag LED wafer nyob deb ntau tshaj ib tug taw tes-qhov chaw lub teeb emission. Lub teeb emission tsam yog feem ntau ib tug ob-seem dav hlau ntawm lub wafers. Txhua atom hla no lub dav hlau muaj ib tug neeg txheej emission cones. Yog nqus tau cov billions ntawm overlapping cones yog tsis yooj yim sua, li ntawd, qhov no yog ib tug yooj yim to taub daim duab uas qhia cov extents ntawm tag nrho cov emission cones ua ke. Qhov loj sab cones yog clipped los qhia rau sab hauv nta thiab txo duab complexity; lawv yuav cuag rau qhov opposite npoo ntawm ob-dimensional emission dav hlau.

Liab qab uncoated semiconductors xws li silicon sau ib tug heev refractive index txheeb ze rau qhib cua, uas tiv thaiv zaj photons mus txog ntawm ntse ces kaum txheeb ze mus rau lub cua-hu nto ntawm lub semiconductor vim tag nrho cov sab hauv thiaj . Qhov no tej khoom vaj tse muaj feem xyuam rau ob lub teeb-emission efficiency ntawm LEDs li zoo raws li lub teeb-haum efficiency ntawm photovoltaic hlwb . Lub refractive index ntawm silicon yog 3.96 (ntawm 590 nm), [50] thaum huab cua yog 1,0002926. [51]

Nyob rau hauv kev, ib tug ca-nto uncoated LED semiconductor nti yuav emit teeb xwb perpendicular mus rau lub semiconductor nto, thiab ib tug ob peb degrees rau sab, nyob rau hauv ib tug lub khob hliav qab zoo xa mus rau raws li lub teeb lub khob hliav qab, lub khob hliav qab ntawm lub teeb, [52] los yog rau txoj kev khiav Lub khob hliav qab. [49] Qhov siab tshaj plaws kaum sab xis ntawm cov xwm txheej no yuav raug xa mus rau li ib qho tseem ceeb lub . Thaum zoo li no lub yog ua zoo tshaj, photons tsis khiav cov semiconductor tab sis yog tsis reflected hauv hauv lub semiconductor siv lead ua raws li yog hais tias nws yog ib tug iav . [49]

Internal reflections yuav khiav los ntawm lwm crystalline ntsej muag yog cov xwm txheej kaum sab xis yog tsis muaj txaus thiab tus siv lead ua yog sufficiently pob tshab tsis rov nqus cov photon emission. Tab sis rau ib tug yooj yim square LED nrog 90-degree angled chaw rau tag nrho cov sab, lub ntsej muag tag nrho ua raws li sib npaug zos lub tsom iav. Nyob rau hauv cov ntaub ntawv no, feem ntau ntawm cov teeb yuav khiav tsis dim thiab yog poob raws li pov tseg thaum tshav kub kub nyob rau hauv lub siv lead ua. [49]

Ib tug convoluted nti nto nrog angled seb zoo li ib tug pob zeb diamond los yog fresnel lens yuav ua rau kom lub teeb tso zis los ntawm qhov uas lub teeb yuav tsum tau tawm txim liab perpendicular mus rau lub nti nto thaum nyob deb mus rau lub tog ntawm lub photon emission point. [53]

Qhov zoo tshaj plaws zoo ntawm ib tug semiconductor nrog lub siab tshaj plaws lub teeb tso zis yuav tsum muaj ib tug microsphere nrog lub photon emission tshwm sim ntawm lub caij nyoog nruab nrab, nrog electrodes tob tob rau qhov chaw hu rau ntawm lub emission point. Tag nrho cov teeb rays emanating los ntawm lub chaw yuav perpendicular mus rau tag nrho saum npoo ntawm tus kheej, ua rau tsis muaj nrog reflections. Ib tug hemispherical semiconductor yuav tseem ua hauj lwm, nrog rau lub tiaj rov qab-nto pab raws li ib daim iav rov qab-tawg khiav ri niab photons. [54]

Transition coatings [ edit ]

Tom qab lub doping ntawm lub wafer , nws yog txiav sib nrug mus rau hauv ib tug neeg hnub . Txhua tuag yog feem ntau hu ua ib tug nti.

Muaj ntau LED semiconductor chips yog encapsulated los yog potted nyob rau hauv kom meej los yog dawb lias molded yas zoo li. Cov yas plhaub muaj peb lub hom phiaj:

  1. Mounting lub semiconductor nti nyob rau hauv pab kiag li lawm yog yooj yim yuav ua kom tiav.

  2. Lub me me taus hluav taws xob thaiv yog lub cev txaus siab thiab muaj kev tiv thaiv ntawm kev puas tsuaj.

  3. Cov yas ua raws li ib tug refractive intermediary ntawm lub kuj high-Performance index semiconductor thiab tsawg-Performance index qhib saum huab cua. [55]

Qhov thib peb feature pab rau boost lub teeb emission los ntawm cov semiconductor los ntawm sawv raws li ib tug diffusing lens, uas lub teeb yuav tsum tau tawm txim liab ntawm ib tug ntau dua lub kaum sab xis ntawm cov xwm txheej ntawm lub teeb lub khob hliav qab dua cov liab qab nti yog tau emit ib leeg.

Efficiency thiab ua hauj lwm zoo tsis [ edit ]

Raug qhia LEDs no yog tsim los ua hauj lwm nrog tsis muaj ntau tshaj li 30-60 milliwatts (mW) ntawm hluav taws xob. Nyob ib ncig ntawm 1999, Philips Lumileds tswvcuab hwj chim LEDs peev xwm ntawm mus siv rau ib tug watt . Cov LEDs siv loj npaum li cas semiconductor tuag ntau thiab tsawg pab lis lub loj hwj chim inputs. Tsis tas li ntawd, lub semiconductor hnub twb mounted mus rau hlau slugs los pub rau thaum tshav kub kub tshem tawm los ntawm lub LED tuag.

Ib tug ntawm cov tseem ceeb zoo ntawm LED-raws li teeb pom kev zoo qhov chaw yog siab luminous miv nyuas siv zug . Dawb LEDs sai sai matched thiab overtook lub miv nyuas siv zug ntawm standard incandescent teeb pom kev zoo systems. Nyob rau hauv 2002, Lumileds ua tsib-watt LEDs muaj nyob nrog luminous miv nyuas siv zug ntawm 18-22 lumens ib watt (lm / W). Kev sib piv, ib tug pa incandescent teeb noob ntawm 60-100 watts emits nyob ib ncig ntawm 15 lm / W, thiab txheej txheem fluorescent teeb emit txog li 100 lm / W.

Raws li ntawm 2012, Philips tau tiav raws li nram no efficacies rau txhua lub xim. [56] Tus efficiency qhov tseem ceeb qhia cov physics - lub teeb hwj chim tawm ib hluav taws xob nyob rau hauv. Cov lumen-ib-watt miv nyuas siv zug nqi no muaj xws li cov yam ntxwv ntawm cov tib neeg qhov muag thiab yog muab tau los siv cov luminosity muaj nuj nqi .


Xim Wavelength ntau (nm) Raug efficiency coefficient Raug miv nyuas siv zug ( lm / W )

liab 620 <> <> 0.39 72

Liab-txiv kab ntxwv 610 <> <> 0.29 98

ntsuab 520 <> <> 0.15 93

Cyan 490 <> <> 0,26 75

Blue 460 <> <> 0.35 37

Nyob rau hauv lub Cuaj Hli Ntuj 2003, ib tug tshiab hom xiav LED twb pom hais tias los ntawm Cree uas kov 24 mW nyob rau hauv 20 milliamperes (MA). Qhov no tsim ib tug muag fej lub teeb dawb muab 65 lm / W nyob rau hauv 20 ma, ua lub brightest dawb LED muag nyob rau hauv lub sij hawm, thiab ntau tshaj plaub lub sij hawm raws li npaum raws li tus qauv incandescents. Nyob rau hauv 2006, lawv pom hais tias nws ib tsab nrog ib cov ntaub ntawv dawb LED luminous miv nyuas siv zug ntawm 131 lm / W nyob rau hauv 20 ma. Nichia Corporation tau tsim ib tug dawb LED nrog luminous miv nyuas siv zug ntawm 150 lm / W ntawm ib tug rau pem hauv ntej tam sim no ntawm 20 ma. [57] Cree lub XLamp XM-L LEDs, muag muaj nyob rau hauv 2011, ua 100 lm / W nyob rau ntawm lawv daim ntawv qhia txog hwj chim ntawm 10 W, thiab mus txog rau 160 lm / W nyob ib ncig ntawm 2 W tswv yim lub hwj chim. Nyob rau hauv 2012, Cree tshaj tawm ib tug dawb LED muab 254 lm / W, [58] thiab 303 lm / W nyob rau hauv lub peb hlis ntuj 2014. [59] Tswv yim general teeb pom kev zoo yuav tsum tau high-power LEDs, ntawm ib watt los yog ntau tshaj. Raug kev khiav hauj lwm currents rau xws li pib thaum 350 ma.

Cov tshem yog lub teeb-emitting diode xwb, nyob rau hauv uas tsis muaj kub nyob rau hauv ib tug lab. Txij li thaum LEDs ntsia tau rau hauv tiag tiag fixtures muaj nyob ntau dua kub thiab nrog tsav tsheb losses, real-ntiaj teb no tshem muaj ntau sab. United States Department of Energy (DOE) kev soj ntsuam ntawm coj mus muag LED teeb tsim los hloov incandescent teeb los yog CFLs pom tias qhov nruab nrab miv nyuas siv zug yog tseem hais txog 46 lm / W nyob rau hauv 2009 (kuaj kev kawm muaj mus txoj los ntawm 17 lm / W rau 79 lm / W). [60]

Efficiency droop [ edit ]

Efficiency droop yog lub txo nyob rau hauv luminous efficiency ntawm LEDs li cov hluav taws xob tam sim no nce saum toj no kaum ntawm milliamperes.

Cov nyhuv no twb pib theorized mus txog rau kom kub. Zaum pov thawj qhov opposite yuav tsis muaj tseeb: txawm hais tias lub neej ntawm ib LED yuav zog, lub efficiency droop yog tsis mob hnyav ntawm txhawb kub. [61] Tus mechanism ua efficiency droop yog tus uas pom nyob rau hauv 2007 raws li auger recombination , uas raug coj nrog mixed cov tshuaj tiv thaiv. [62] Nyob rau hauv 2013, ib txoj kev tshawb paub tseeb hais tias auger recombination li qhov ua rau ntawm efficiency droop. [63]

Nyob rau hauv tas li ntawd mus rau tsawg npaum, kev khiav hauj lwm LEDs dua fais currents tsim dua thaum tshav kub kub theem uas nruab nrab hauv lub neej ntawm lub LED. Vim hais tias ntawm no nce cua kub dua dej tsaws ntxhee, high-brightness LEDs muaj ib tug kev lag luam txheem ntawm kev khiav hauj lwm ntawm xwb 350 MA, uas yog ib tug hais nruab nrab ntawm lub teeb tso zis, efficiency, thiab thiav. [62] [64] [65] [66]

Tau cov ntsiab [ edit ]

Es tsis txhob ua tam sim no ntau ntau, luminance yog feem ntau zog los ntawm combining ntau LEDs nyob rau hauv ib tug noob. Daws cov teeb meem ntawm cov efficiency droop yuav txhais hais tias tsev neeg LED qhov muag teeb yuav tsum tau tsawg dua LEDs, uas yuav txo tau cov nqi.

Soj ntsuam ntawm nyob rau hauv lub US Naval tshawb fawb Laboratory tau pom ib txoj kev thim cov efficiency droop. Lawv nrhiav tau tias tus droop tshwm sim los ntawm uas tsis yog-radiative auger recombination ntawm lub txhaj muaj. Lawv tsim quantum dej nrog ib tug mos mos twj ywm tej zaum yuav thim qhov uas tsis yog-radiative auger dab. [67]

Soj ntsuam ntawm nyob Taiwan National Central University thiab Epistar Corp tsim muaj ib txoj kev thim cov efficiency droop los ntawm kev siv tej hub txhuas nitride (AlN) substrates, uas muaj ntau thermally conductive tshaj lub lag luam siv sapphire. Lub siab dua thermal conductivity thiaj li self-cua sov los. [68]

Lub neej thiab tsis ua hauj lwm [ edit ]

Main tsab xov xwm: Daim ntawv teev cov LED tsis ua hauj lwm hom

Tau-lub xeev pab kiag li lawm xws li LEDs no yuav heev tsawg coj thiab tsim kua muag yog tias ua thaum uas tsis muaj dej tsaws ntxhee thiab tsis sov. Raug lifetimes hais yog 25,000 100,000 teev, tab sis thaum tshav kub kub thiab tam sim no tej chaw uas yuav cuag los yog kom lub sij hawm no ho. [69]

Feem ntau cov tsos mob ntawm LED (thiab diode laser ) tsis ua hauj lwm yog cov gradual txos ntawm lub teeb tso zis thiab tsis ua hauj lwm zoo. Sudden failures, txawm hais tias tsis tshua muaj, kuj yuav tshwm sim. Early liab LEDs twb notable rau lawv luv luv pab lub neej. Nrog rau txoj kev loj hlob ntawm high-power LEDs, lub pab kiag li lawm yog raug mus rau qib siab hlws ris kub thiab ntau dua tam sim no densities dua tsoos pab kiag li lawm. Qhov no ua rau kev nyuaj siab nyob rau hauv cov khoom thiab tej zaum yuav ua rau thaum ntxov lub teeb-output degradation. Yuav kom quantitatively cais pab lub neej nyob rau hauv ib tug zoo yam nws twb tau pom los siv L70 los yog L50, uas yog cov runtimes (feem ntau muab nyob rau hauv txhiab ntawm cov xuaj moos) uas ib tug muab LED nce mus txog 70% thiab 50% ntawm thawj zaug teeb tso zis, ntsig txog. [70]

Whereas nyob rau hauv feem ntau yav dhau los qhov chaw ntawm lub teeb (incandescent teeb, paug teeb, thiab cov uas hlawv combustible roj, xws li tswm ciab thiab roj teeb) lub teeb tau los ntawm tshav kub, LEDs tsuas khiav lag luam yog hais tias lawv yog khaws cia txias txaus. Cov chaw tsim tshuaj paus feem ntau qhia txog ib tug tshaj plaws hlws ris kub ntawm 125 los yog 150 ° C, thiab txo kub hu nyob rau hauv qhov kev txaus siab ntawm lub neej ntev. Thaum cov kub, kuj me me thaum tshav kub kub yog poob los ntawm tawg, uas txhais tau tias cov teeb beam generated los ntawm ib tug LED yog txias.

Lub pov tseg thaum tshav kub kub nyob rau hauv ib tug high-power LED (uas raws li ntawm 2015 yuav ua tau tsawg tshaj li ib nrab lub hwj chim uas nws kov) yog conveyed los ntawm conduction ntawm lub substrate thiab pob ntawm lub LED mus rau ib tug kub lub dab ntxuav tes , uas muab lub cua sov rau lub ambient huab cua los ntawm convection. Ceev faj thermal tsim yog, yog li ntawd, qhov tseem ceeb, noj mus rau hauv tus account lub thermal resistances ntawm lub LED lub pob, lub tshav kub dab ntxuav tes thiab lub interface ntawm ob. Medium-hwj chim LEDs yog feem ntau tsim los soldered ncaj qha mus rau ib tug luam Circuit Court board uas muaj ib tug thermally conductive hlau txheej. High-power LEDs yog fej nyob rau hauv loj-cheeb tsam tej hub pob uas tsim los txuas mus rau ib tug hlau kub tog , lub interface ua ib cov khoom uas muaj thermal conductivity ( thermal roj , theem-hloov cov ntaub ntawv uas , thermally conductive ncoo los yog thermal nplaum ).

Yog hais tias ib tug LED-raws li lub teeb yog ntsia tau rau hauv ib tug unventilated luminaire , los yog ib tug luminaire yog nyob rau hauv ib qho chaw uas tsis muaj free cua kev, lub LED yog yuav overheat, uas ua rau txo lub neej los yog thaum ntxov catastrophic tsis ua hauj lwm. Thermal tsim yog feem ntau raws li ib tug ambient kub ntawm 25 ° C (77 ° F). LEDs siv nyob rau hauv sab nraum zoov siv, xws li tsheb Pib ntsais koj teeb los yog nyob rau hauv-pavement teeb liab teeb, thiab nyob rau hauv cov huab cua nyob qhov twg qhov kub thiab txias nyob rau hauv lub teeb fixture tau txais heev, yuav muaj kev txo zis los yog txawm tsis ua hauj lwm. [71]

Txij li thaum LED miv nyuas siv zug yog siab dua thaum uas tsis muaj kub, LED technology yog zoo suited rau tsev loj freezer teeb pom kev zoo. [72] [73] [74] Vim hais tias LEDs tsim tsawg pov tseg thaum tshav kub kub tshaj incandescent teeb, lawv siv nyob rau hauv yees khov nab kuab yuav txuag rau tub yees nqi zoo li. Txawm li cas los, lawv tej zaum yuav raug rau te thiab daus buildup tshaj incandescent teeb, [71] li ib co LED teeb pom kev zoo systems tau tsim nrog ib tug ntxiv cua kub Circuit Court. Tsis tas li ntawd, kev tshawb fawb tau tsim thaum tshav kub kub lub dab ntxuav tes technologies uas yuav hloov thaum tshav kub kub ua nyob rau hauv lub hlws ris rau qhov hauv lub teeb fixture. [75]

Xim thiab cov ntaub ntawv [ edit ]

Pa LEDs yog ua los ntawm ib tug ntau yam ntawm inorganic semiconductor ntaub ntawv . Cov nram qab no cov lus qhia tau hais tias cov muaj xim nrog wavelength ntau, voltage nco, thiab cov ntaub ntawv:


Xim Wavelength [nm] Voltage nco [ΔV] semiconductor khoom

Infrared λ > 760 Δ V <> Gallium arsenide (GaAs)
Aluminium gallium arsenide (AlGaAs)

liab 610 <> <> 1,63 <δ>V <> Aluminium gallium arsenide (AlGaAs)
Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaInP)
Gallium (III) phosphide (GAP)

Txiv kab ntxwv 590 <> <> 2,03 <δ>V <> Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaInP)
Gallium (III) phosphide (GAP)

Daj 570 <> <> 2.10 <δ>V <> Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaInP)
Gallium (III) phosphide (GAP)

ntsuab 500 <> <> 1.9 [76] <δ>V <> Tsoos ntsuab:
Gallium (III) phosphide (GAP)
Aluminium gallium indium phosphide (AlGaInP)
Aluminium gallium phosphide (AlGaP)
Ntshiab ntsuab:
Indium gallium nitride (InGaN) / Gallium (III) nitride (GaN)

Blue 450 <> <> 2,48 <δ>V <> Zinc selenide (ZnSe)
Indium gallium nitride (InGaN)
Silicon carbide (sic) raws li substrate
Silicon (Si) raws li substrate-nyob rau hauv txoj kev loj hlob

violet 400 <> <> 2,76 <δ>V <> Indium gallium nitride (InGaN)

Ntshav Ntau hom 2,48 <δ>V <> Dual xiav / liab LEDs,
xiav nrog liab phosphor,
los yog dawb nrog liab doog yas

ultraviolet λ <> 3 <δ>V <> Indium gallium nitride (InGaN) (385-400 nm)

Pob zeb diamond (235 nm) [77]
Boron nitride (215 nm) [78] [79]
Aluminium nitride (AlN) (210 nm) [80]
Aluminium gallium nitride (AlGaN)
Aluminium gallium indium nitride (AlGaInN) -down rau 210 nm [81]


liab dawb Ntau hom Δ V ~ 3.3 [82] Blue nrog ib tug los yog ob tug phosphor khaubncaws sab nraud povtseg,
daj nrog liab, txiv kab ntxwv los yog liab phosphor ntxiv afterwards,

dawb nrog liab yas,
los yog dawb phosphors nrog cov liab xim los yog cov xim tshaj sab saum toj. [83]


Dawb broad spectrum 2.8 <δ>V <> Cool / Ntshiab Dawb: Blue / UV diode nrog daj phosphor
Sov Dawb: Blue diode nrog txiv kab ntxwv phosphor

Xiav thiab ultraviolet [ edit ]

Blue LEDs

Sab nraud video
Tshuaj ntsuab Maruska thawj xiav LED College of New Jersey Sarnoff Collection.png
"Lub Thawj Blue LED" , Tshuaj cuab yeej cuab tam Foundation

The first blue-violet LED using magnesium-doped gallium nitride was made at Stanford University in 1972 by Herb Maruska and Wally Rhines, doctoral students in materials science and engineering. [84] [85] At the time Maruska was on leave from RCA Laboratories , where he collaborated with Jacques Pankove on related work. In 1971, the year after Maruska left for Stanford, his RCA colleagues Pankove and Ed Miller demonstrated the first blue electroluminescence from zinc-doped gallium nitride, though the subsequent device Pankove and Miller built, the first actual gallium nitride light-emitting diode, emitted green light. [86] [87] In 1974 the US Patent Office awarded Maruska, Rhines and Stanford professor David Stevenson a patent for their work in 1972 (US Patent US3819974 A ) and today magnesium-doping of gallium nitride continues to be the basis for all commercial blue LEDs and laser diodes. These devices built in the early 1970s had too little light output to be of practical use and research into gallium nitride devices slowed. In August 1989, Cree introduced the first commercially available blue LED based on the indirect bandgap semiconductor, silicon carbide (SiC). [88] SiC LEDs had very low efficiency, no more than about 0.03%, but did emit in the blue portion of the visible light spectrum. [ citation needed ]

In the late 1980s, key breakthroughs in GaN epitaxial growth and p-type doping [89] ushered in the modern era of GaN-based optoelectronic devices. Building upon this foundation, Theodore Moustakas at Boston University patented a method for producing high-brightness blue LEDs using a new two-step process. [90] Two years later, in 1993, high-brightness blue LEDs were demonstrated again by Shuji Nakamura of Nichia Corporation using a gallium nitride growth process similar to Moustakas's. [91] Both Moustakas and Nakamura were issued separate patents, which confused the issue of who was the original inventor (partly because although Moustakas invented his first, Nakamura filed first). [ citation needed ] This new development revolutionized LED lighting, making high-power blue light sources practical, leading to the development of technologies like Blu-ray , as well as allowing the bright high-resolution screens of modern tablets and phones. [ citation needed ]

Nakamura was awarded the 2006 Millennium Technology Prize for his invention. [92] Nakamura, Hiroshi Amano and Isamu Akasaki were awarded the Nobel Prize in Physics in 2014 for the invention of the blue LED. [93] [94] [95] In 2015, a US court ruled that three companies (ie the litigants who had not previously settled out of court) that had licensed Nakamura's patents for production in the United States had infringed Moustakas's prior patent, and ordered them to pay licensing fees of not less than 13 million USD. [96]

By the late 1990s, blue LEDs became widely available. They have an active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN, called cladding layers. By varying the relative In/Ga fraction in the InGaN quantum wells, the light emission can in theory be varied from violet to amber. Aluminium gallium nitride (AlGaN) of varying Al/Ga fraction can be used to manufacture the cladding and quantum well layers for ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological maturity of InGaN/GaN blue/green devices. If un-alloyed GaN is used in this case to form the active quantum well layers, the device will emit near-ultraviolet light with a peak wavelength centred around 365 nm. Green LEDs manufactured from the InGaN/GaN system are far more efficient and brighter than green LEDs produced with non-nitride material systems, but practical devices still exhibit efficiency too low for high-brightness applications. [ citation needed ]

With nitrides containing aluminium, most often AlGaN and AlGaInN , even shorter wavelengths are achievable. Ultraviolet LEDs in a range of wavelengths are becoming available on the market. Near-UV emitters at wavelengths around 375–395 nm are already cheap and often encountered, for example, as black light lamp replacements for inspection of anti- counterfeiting UV watermarks in some documents and paper currencies. Shorter-wavelength diodes, while substantially more expensive, are commercially available for wavelengths down to 240 nm. [97] As the photosensitivity of microorganisms approximately matches the absorption spectrum of DNA , with a peak at about 260 nm, UV LED emitting at 250–270 nm are to be expected in prospective disinfection and sterilization devices. Recent research has shown that commercially available UVA LEDs (365 nm) are already effective disinfection and sterilization devices. [98] UV-C wavelengths were obtained in laboratories using aluminium nitride (210 nm), [80] boron nitride (215 nm) [78] [79] and diamond (235 nm). [77]

RGB [ edit ]

RGB-SMD-LED

RGB LEDs consist of one red, one green, and one blue LED. By independently adjusting each of the three, RGB LEDs are capable of producing a wide color gamut . Unlike dedicated-color LEDs, however, these obviously do not produce pure wavelengths. Moreover, such modules as commercially available are often not optimized for smooth color mixing.

White [ edit ]

There are two primary ways of producing white light-emitting diodes (WLEDs), LEDs that generate high-intensity white light. One is to use individual LEDs that emit three primary colors [99] —red, green, and blue—and then mix all the colors to form white light. The other is to use a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light, much in the same way a fluorescent light bulb works. It is important to note that the 'whiteness' of the light produced is essentially engineered to suit the human eye, and depending on the situation it may not always be appropriate to think of it as white light.

There are three main methods of mixing colors to produce white light from an LED:

  • blue LED + green LED + red LED (color mixing; can be used as backlighting for displays, extremely poor for illumination due to gaps in spectrum)

  • near-UV or UV LED + RGB phosphor (an LED producing light with a wavelength shorter than blue's is used to excite an RGB phosphor)

  • blue LED + yellow phosphor (two complementary colors combine to form white light; more efficient than first two methods and more commonly used) [100]

Because of metamerism , it is possible to have quite different spectra that appear white. However, the appearance of objects illuminated by that light may vary as the spectrum varies, this is the issue of Colour rendition, quite separate from Colour Temperature, where a really orange or cyan object could appear with the wrong colour and much darker as the LED or phosphor does not emit the wavelength. The best colour rendition CFL and LEDs use a mix of phosphors, resulting in less efficiency but better quality of light. Though incandescent halogen lamps have a more orange colour temperature, they are still the best easily available artificial light sources in terms of colour rendition.

RGB systems [ edit ]

Combined spectral curves for blue, yellow-green, and high-brightness red solid-state semiconductor LEDs. FWHM spectral bandwidth is approximately 24–27 nm for all three colors.



RGB LED

White light can be formed by mixing differently colored lights; the most common method is to use red, green, and blue (RGB). Hence the method is called multi-color white LEDs (sometimes referred to as RGB LEDs). Because these need electronic circuits to control the blending and diffusion of different colors, and because the individual color LEDs typically have slightly different emission patterns (leading to variation of the color depending on direction) even if they are made as a single unit, these are seldom used to produce white lighting. Nonetheless, this method has many applications because of the flexibility of mixing different colors, [101] and in principle, this mechanism also has higher quantum efficiency in producing white light. [ citation needed ]

There are several types of multi-color white LEDs: di- , tri- , and tetrachromatic white LEDs. Several key factors that play among these different methods include color stability, color rendering capability, and luminous efficacy. Often, higher efficiency will mean lower color rendering, presenting a trade-off between the luminous efficacy and color rendering. For example, the dichromatic white LEDs have the best luminous efficacy (120 lm/W), but the lowest color rendering capability. However, although tetrachromatic white LEDs have excellent color rendering capability, they often have poor luminous efficacy. Trichromatic white LEDs are in between, having both good luminous efficacy (>70 lm/W) and fair color rendering capability.

One of the challenges is the development of more efficient green LEDs. The theoretical maximum for green LEDs is 683 lumens per watt but as of 2010 few green LEDs exceed even 100 lumens per watt. The blue and red LEDs get closer to their theoretical limits.

Multi-color LEDs offer not merely another means to form white light but a new means to form light of different colors. Most perceivable colors can be formed by mixing different amounts of three primary colors. This allows precise dynamic color control. As more effort is devoted to investigating this method, multi-color LEDs should have profound influence on the fundamental method that we use to produce and control light color. However, before this type of LED can play a role on the market, several technical problems must be solved. These include that this type of LED's emission power decays exponentially with rising temperature, [102] resulting in a substantial change in color stability. Such problems inhibit and may preclude industrial use. Thus, many new package designs aimed at solving this problem have been proposed and their results are now being reproduced by researchers and scientists. However multi-colour LEDs without phosphors can never provide good quality lighting because each LED is a narrow band source (see graph). LEDs without phosphor while a poorer solution for general lighting are the best solution for displays, either backlight of LCD, or direct LED based pixels.

Correlated color temperature (CCT) dimming for LED technology is regarded as a difficult task since binning, age and temperature drift effects of LEDs change the actual color value output. Feedback loop systems are used for example with color sensors, to actively monitor and control the color output of multiple color mixing LEDs. [103]

Phosphor-based LEDs [ edit ]

Spectrum of a white LED showing blue light directly emitted by the GaN-based LED (peak at about 465 nm) and the more broadband Stokes-shifted light emitted by the Ce 3+ :YAG phosphor, which emits at roughly 500–700 nm

This method involves coating LEDs of one color (mostly blue LEDs made of InGaN ) with phosphors of different colors to form white light; the resultant LEDs are called phosphor-based or phosphor-converted white LEDs (pcLEDs). [104] A fraction of the blue light undergoes the Stokes shift being transformed from shorter wavelengths to longer. Depending on the color of the original LED, phosphors of different colors can be employed. If several phosphor layers of distinct colors are applied, the emitted spectrum is broadened, effectively raising the color rendering index (CRI) value of a given LED. [105]

Phosphor-based LED efficiency losses are due to the heat loss from the Stokes shift and also other phosphor-related degradation issues. Their luminous efficacies compared to normal LEDs depend on the spectral distribution of the resultant light output and the original wavelength of the LED itself. For example, the luminous efficacy of a typical YAG yellow phosphor based white LED ranges from 3 to 5 times the luminous efficacy of the original blue LED because of the human eye's greater sensitivity to yellow than to blue (as modeled in the luminosity function ). Due to the simplicity of manufacturing, the phosphor method is still the most popular method for making high-intensity white LEDs. The design and production of a light source or light fixture using a monochrome emitter with phosphor conversion is simpler and cheaper than a complex RGB system, and the majority of high-intensity white LEDs presently on the market are manufactured using phosphor light conversion.

Among the challenges being faced to improve the efficiency of LED-based white light sources is the development of more efficient phosphors. As of 2010, the most efficient yellow phosphor is still the YAG phosphor, with less than 10% Stokes shift loss. Losses attributable to internal optical losses due to re-absorption in the LED chip and in the LED packaging itself account typically for another 10% to 30% of efficiency loss. Currently, in the area of phosphor LED development, much effort is being spent on optimizing these devices to higher light output and higher operation temperatures. For instance, the efficiency can be raised by adapting better package design or by using a more suitable type of phosphor. Conformal coating process is frequently used to address the issue of varying phosphor thickness.

Some phosphor-based white LEDs encapsulate InGaN blue LEDs inside phosphor-coated epoxy. Alternatively, the LED might be paired with a remote phosphor, a preformed polycarbonate piece coated with the phosphor material. Remote phosphors provide more diffuse light, which is desirable for many applications. Remote phosphor designs are also more tolerant of variations in the LED emissions spectrum. A common yellow phosphor material is cerium - doped yttrium aluminium garnet (Ce 3+ :YAG).

White LEDs can also be made by coating near- ultraviolet (NUV) LEDs with a mixture of high-efficiency europium -based phosphors that emit red and blue, plus copper and aluminium-doped zinc sulfide (ZnS:Cu, Al) that emits green. This is a method analogous to the way fluorescent lamps work. This method is less efficient than blue LEDs with YAG:Ce phosphor, as the Stokes shift is larger, so more energy is converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both methods offer comparable brightness. A concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin.

Other white LEDs [ edit ]

Another method used to produce experimental white light LEDs used no phosphors at all and was based on homoepitaxially grown zinc selenide (ZnSe) on a ZnSe substrate that simultaneously emitted blue light from its active region and yellow light from the substrate. [106]

A new style of wafers composed of gallium-nitride-on-silicon (GaN-on-Si) is being used to produce white LEDs using 200-mm silicon wafers. This avoids the typical costly sapphire substrate in relatively small 100- or 150-mm wafer sizes. [107] The sapphire apparatus must be coupled with a mirror-like collector to reflect light that would otherwise be wasted. It is predicted that by 2020, 40% of all GaN LEDs will be made with GaN-on-Si. Manufacturing large sapphire material is difficult, while large silicon material is cheaper and more abundant. LED companies shifting from using sapphire to silicon should be a minimal investment. [108]

Organic light-emitting diodes (OLEDs) [ edit ]

Main article: Organic light-emitting diode

Demonstration of a flexible OLED device

Orange light-emitting diode

In an organic light-emitting diode ( OLED ), the electroluminescent material comprising the emissive layer of the diode is an organic compound . The organic material is electrically conductive due to the delocalization of pi electrons caused by conjugation over all or part of the molecule, and the material therefore functions as an organic semiconductor . [109] The organic materials can be small organic molecules in a crystalline phase , or polymers . [110]

The potential advantages of OLEDs include thin, low-cost displays with a low driving voltage, wide viewing angle, and high contrast and color gamut. [111] Polymer LEDs have the added benefit of printable and flexible displays. [112] [113] [114] OLEDs have been used to make visual displays for portable electronic devices such as cellphones, digital cameras, and MP3 players while possible future uses include lighting and televisions. [110] [111]

Quantum dot LEDs [ edit ]

See also: quantum dot display

Quantum dots (QD) are semiconductor nanocrystals whose optical properties allow their emission color to be tuned from the visible into the infrared spectrum. [115] [116] This allows quantum dot LEDs to create almost any color on the CIE diagram. This provides more color options and better color rendering than white LEDs since the emission spectrum is much narrower, characteristic of quantum confined states.

There are two types of schemes for QD excitation. One uses photo excitation with a primary light source LED (typically blue or UV LEDs are used). The other is direct electrical excitation first demonstrated by Alivisatos et al. [117]

One example of the photo-excitation scheme is a method developed by Michael Bowers, at Vanderbilt University in Nashville, involving coating a blue LED with quantum dots that glow white in response to the blue light from the LED. This method emits a warm, yellowish-white light similar to that made by incandescent light bulbs . [118] Quantum dots are also being considered for use in white light-emitting diodes in liquid crystal display (LCD) televisions. [119]

In February 2011 scientists at PlasmaChem GmbH were able to synthesize quantum dots for LED applications and build a light converter on their basis, which was able to efficiently convert light from blue to any other color for many hundred hours. [120] Such QDs can be used to emit visible or near infrared light of any wavelength being excited by light with a shorter wavelength.

The structure of QD-LEDs used for the electrical-excitation scheme is similar to basic design of OLEDs . A layer of quantum dots is sandwiched between layers of electron-transporting and hole-transporting materials. An applied electric field causes electrons and holes to move into the quantum dot layer and recombine forming an exciton that excites a QD. This scheme is commonly studied for quantum dot display . The tunability of emission wavelengths and narrow bandwidth is also beneficial as excitation sources for fluorescence imaging. Fluorescence near-field scanning optical microscopy ( NSOM ) utilizing an integrated QD-LED has been demonstrated. [121]

In February 2008, a luminous efficacy of 300 lumens of visible light per watt of radiation (not per electrical watt) and warm-light emission was achieved by using nanocrystals . [122]

Types [ edit ]

LEDs are produced in a variety of shapes and sizes. The color of the plastic lens is often the same as the actual color of light emitted, but not always. For instance, purple plastic is often used for infrared LEDs, and most blue devices have colorless housings. Modern high-power LEDs such as those used for lighting and backlighting are generally found in surface-mount technology (SMT) packages (not shown).

The main types of LEDs are miniature, high-power devices and custom designs such as alphanumeric or multi-color. [123]

Miniature [ edit ]

Photo of miniature surface mount LEDs in most common sizes. They can be much smaller than a traditional 5 mm lamp type LED which is shown on the upper left corner.


Very small (1.6x1.6x0.35 mm) red, green, and blue surface mount miniature LED package with gold wire bonding details.

These are mostly single-die LEDs used as indicators, and they come in various sizes from 2 mm to 8 mm, through-hole and surface mount packages. They usually do not use a separate heat sink . [124] Typical current ratings range from around 1 mA to above 20 mA. The small size sets a natural upper boundary on power consumption due to heat caused by the high current density and need for a heat sink. Often daisy chained as used in LED tapes .

Common package shapes include round, with a domed or flat top, rectangular with a flat top (as used in bar-graph displays), and triangular or square with a flat top. The encapsulation may also be clear or tinted to improve contrast and viewing angle.

Researchers at the University of Washington have invented the thinnest LED. It is made of two-dimensional (2-D) flexible materials. It is three atoms thick, which is 10 to 20 times thinner than three-dimensional (3-D) LEDs and is also 10,000 times smaller than the thickness of a human hair. These 2-D LEDs are going to make it possible to create smaller, more energy-efficient lighting, optical communication and nano lasers . [125]

There are three main categories of miniature single die LEDs:

Low-current


Typically rated for 2mA at around 2V (approximately 4mW consumption)

Standard 20mA LEDs (ranging from approximately 40mW to 90mW) at around:
  • 1.9 to 2.1V for red, orange, yellow, and traditional green

  • 3.0 to 3.4V for pure green and blue

  • 2.9 to 4.2V for violet, pink, purple and white

Ultra-high-output


20mA at approximately 2 or 4–5V, designed for viewing in direct sunlight 5V and 12VLEDs are ordinary miniature LEDs that incorporate a suitable series   resistor for direct connection to a 5V or 12V supply.

High-power [ edit ]

High-power light-emitting diodes attached to an LED star base ( Luxeon , Lumileds )See also: Solid-state lighting , LED lamp , and Thermal management of high-power LEDs

High-power LEDs (HP-LEDs) or high-output LEDs (HO-LEDs) can be driven at currents from hundreds of mA to more than an ampere, compared with the tens of mA for other LEDs. Some can emit over a thousand lumens. [126] [127] LED power densities up to 300 W/cm 2 have been achieved. [128] Since overheating is destructive, the HP-LEDs must be mounted on a heat sink to allow for heat dissipation. If the heat from an HP-LED is not removed, the device will fail in seconds. One HP-LED can often replace an incandescent bulb in a flashlight , or be set in an array to form a powerful LED lamp .

Some well-known HP-LEDs in this category are the Nichia 19 series, Lumileds Rebel Led, Osram Opto Semiconductors Golden Dragon, and Cree X-lamp. As of September 2009, some HP-LEDs manufactured by Cree now exceed 105 lm/W. [129]

Examples for Haitz's law , which predicts an exponential rise in light output and efficacy of LEDs over time, are the CREE XP-G series LED which achieved 105 lm/W in 2009 [129] and the Nichia 19 series with a typical efficacy of 140 lm/W, released in 2010. [130]

AC driven [ edit ]

LEDs have been developed by Seoul Semiconductor that can operate on AC power without the need for a DC converter. For each half-cycle, part of the LED emits light and part is dark, and this is reversed during the next half-cycle. The efficacy of this type of HP-LED is typically 40 lm/W. [131] A large number of LED elements in series may be able to operate directly from line voltage. In 2009, Seoul Semiconductor released a high DC voltage LED, named as 'Acrich MJT', capable of being driven from AC power with a simple controlling circuit. The low-power dissipation of these LEDs affords them more flexibility than the original AC LED design. [132]

Application-specific variations [ edit ]

Flashing [ edit ]

Flashing LEDs are used as attention seeking indicators without requiring external electronics. Flashing LEDs resemble standard LEDs but they contain an integrated multivibrator circuit that causes the LED to flash with a typical period of one second. In diffused lens LEDs, this circuit is visible as a small black dot. Most flashing LEDs emit light of one color, but more sophisticated devices can flash between multiple colors and even fade through a color sequence using RGB color mixing.

Bi-color [ edit ]

Bi-color LEDs contain two different LED emitters in one case. There are two types of these. One type consists of two dies connected to the same two leads antiparallel to each other. Current flow in one direction emits one color, and current in the opposite direction emits the other color. The other type consists of two dies with separate leads for both dies and another lead for common anode or cathode so that they can be controlled independently. The most common bi-color combination is red/traditional green, however, other available combinations include amber/traditional green, red/pure green, red/blue, and blue/pure green.

Tri-color [ edit ]

Tri-color LEDs contain three different LED emitters in one case. Each emitter is connected to a separate lead so they can be controlled independently. A four-lead arrangement is typical with one common lead (anode or cathode) and an additional lead for each color.

RGB [ edit ]

RGB LEDs are tri-color LEDs with red, green, and blue emitters, in general using a four-wire connection with one common lead (anode or cathode). These LEDs can have either common positive or common negative leads. Others, however, have only two leads (positive and negative) and have a built-in tiny electronic control unit .

Decorative-multicolor [ edit ]

Decorative-multicolor LEDs incorporate several emitters of different colors supplied by only two lead-out wires. Colors are switched internally by varying the supply voltage.

Alphanumeric [ edit ]

Alphanumeric LEDs are available in seven-segment , starburst , and dot-matrix format. Seven-segment displays handle all numbers and a limited set of letters. Starburst displays can display all letters. Dot-matrix displays typically use 5x7 pixels per character. Seven-segment LED displays were in widespread use in the 1970s and 1980s, but rising use of liquid crystal displays , with their lower power needs and greater display flexibility, has reduced the popularity of numeric and alphanumeric LED displays.

Digital-RGB [ edit ]

Digital-RGB LEDs are RGB LEDs that contain their own "smart" control electronics. In addition to power and ground, these provide connections for data-in, data-out, and sometimes a clock or strobe signal. These are connected in a daisy chain , with the data in of the first LED sourced by a microprocessor, which can control the brightness and color of each LED independently of the others. They are used where a combination of maximum control and minimum visible electronics are needed such as strings for Christmas and LED matrices. Some even have refresh rates in the kHz range, allowing for basic video applications.

Filament [ edit ]

An LED filament consists of multiple LED chips connected in series on a common longitudinal substrate that forms a thin rod reminiscent of a traditional incandescent filament. [133] These are being used as a low-cost decorative alternative for traditional light bulbs that are being phased out in many countries. The filaments require a rather high voltage to light to nominal brightness, allowing them to work efficiently and simply with mains voltages. Often a simple rectifier and capacitive current limiting are employed to create a low-cost replacement for a traditional light bulb without the complexity of creating a low voltage, high current converter which is required by single die LEDs. [134] Usually, they are packaged in a sealed enclosure with a shape similar to lamps they were designed to replace (eg a bulb) and filled with inert nitrogen or carbon dioxide gas to remove heat efficiently.

Considerations for use [ edit ]

Power sources [ edit ]

Main article: LED power sources

Simple LED circuit with resistor for current limiting

The current–voltage characteristic of an LED is similar to other diodes, in that the current is dependent exponentially on the voltage (see Shockley diode equation ). This means that a small change in voltage can cause a large change in current. [135] If the applied voltage exceeds the LED's forward voltage drop by a small amount, the current rating may be exceeded by a large amount, potentially damaging or destroying the LED. The typical solution is to use constant-current power supplies to keep the current below the LED's maximum current rating. Since most common power sources (batteries, mains) are constant-voltage sources, most LED fixtures must include a power converter, at least a current-limiting resistor. However, the high resistance of three-volt coin cells combined with the high differential resistance of nitride-based LEDs makes it possible to power such an LED from such a coin cell without an external resistor.

Electrical polarity [ edit ]

Main article: Electrical polarity of LEDs

As with all diodes, current flows easily from p-type to n-type material. [136] However, no current flows and no light is emitted if a small voltage is applied in the reverse direction. If the reverse voltage grows large enough to exceed the breakdown voltage , a large current flows and the LED may be damaged. If the reverse current is sufficiently limited to avoid damage, the reverse-conducting LED is a useful noise diode .

Safety and health [ edit ]

The vast majority of devices containing LEDs are "safe under all conditions of normal use", and so are classified as "Class 1 LED product"/"LED Klasse 1". At present, only a few LEDs—extremely bright LEDs that also have a tightly focused viewing angle of 8° or less—could, in theory, cause temporary blindness, and so are classified as "Class 2". [137] The opinion of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) of 2010, on the health issues concerning LEDs, suggested banning public use of lamps which were in the moderate Risk Group 2, especially those with a high blue component in places frequented by children. [138] In general, laser safety regulations—and the "Class 1", "Class 2", etc. system—also apply to LEDs. [139]

While LEDs have the advantage over fluorescent lamps that they do not contain mercury , they may contain other hazardous metals such as lead and arsenic . Regarding the toxicity of LEDs when treated as waste, a study published in 2011 stated: "According to federal standards, LEDs are not hazardous except for low-intensity red LEDs, which leached Pb [lead] at levels exceeding regulatory limits (186 mg/L; regulatory limit: 5). However, according to California regulations, excessive levels of copper (up to 3892 mg/kg; limit: 2500), lead (up to 8103 mg/kg; limit: 1000), nickel (up to 4797 mg/kg; limit: 2000), or silver (up to 721 mg/kg; limit: 500) render all except low-intensity yellow LEDs hazardous." [140]

In 2016 a statement of the American Medical Association (AMA) concerning the possible influence of blueish street lighting on the sleep-wake cycle of city-dwellers led to some controversy. So far high-pressure sodium lamps (HPS) with an orange light spectrum were the most efficient light sources commonly used in street-lighting. Now many modern street lamps are equipped with Indium gallium nitride LEDs (InGaN). These are even more efficient and mostly emit blue-rich light with a higher correlated color temperature (CCT) . Since light with a high CCT resembles daylight it is thought that this might have an effect on the normal circadian physiology by suppressing melatonin production in the human body. There have been no relevant studies as yet and critics claim exposure levels are not high enough to have a noticeable effect. [141]

Advantages [ edit ]

  • Efficiency: LEDs emit more lumens per watt than incandescent light bulbs. [142] The efficiency of LED lighting fixtures is not affected by shape and size, unlike fluorescent light bulbs or tubes.

  • Color: LEDs can emit light of an intended color without using any color filters as traditional lighting methods need. This is more efficient and can lower initial costs.

  • Size: LEDs can be very small (smaller than 2 mm 2 [143] ) and are easily attached to printed circuit boards.

  • Warmup time: LEDs light up very quickly. A typical red indicator LED will achieve full brightness in under a microsecond . [144] LEDs used in communications devices can have even faster response times.

  • Cycling: LEDs are ideal for uses subject to frequent on-off cycling, unlike incandescent and fluorescent lamps that fail faster when cycled often, or high-intensity discharge lamps (HID lamps) that require a long time before restarting.

  • Dimming: LEDs can very easily be dimmed either by pulse-width modulation or lowering the forward current. [145] This pulse-width modulation is why LED lights, particularly headlights on cars, when viewed on camera or by some people, appear to be flashing or flickering. This is a type of stroboscopic effect .

  • Cool light: In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED.

  • Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt failure of incandescent bulbs. [69]

  • Lifetime: LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be longer. [146] Fluorescent tubes typically are rated at about 10,000 to 15,000 hours, depending partly on the conditions of use, and incandescent light bulbs at 1,000 to 2,000 hours. Several DOE demonstrations have shown that reduced maintenance costs from this extended lifetime, rather than energy savings, is the primary factor in determining the payback period for an LED product. [147]

  • Shock resistance: LEDs, being solid-state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs, which are fragile.

  • Focus: The solid package of the LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner. For larger LED packages total internal reflection (TIR) lenses are often used to the same effect. However, when large quantities of light are needed many light sources are usually deployed, which are difficult to focus or collimate towards the same target.

Disadvantages [ edit ]

  • Initial price: LEDs are currently slightly more expensive (price per lumen) on an initial capital cost basis, than other lighting technologies. As of March 2014, at least one manufacturer claims to have reached $1 per kilolumen. [148] The additional expense partially stems from the relatively low lumen output and the drive circuitry and power supplies needed.

  • Temperature dependence: LED performance largely depends on the ambient temperature of the operating environment – or thermal management properties. Overdriving an LED in high ambient temperatures may result in overheating the LED package, eventually leading to device failure. An adequate heat sink is needed to maintain long life. This is especially important in automotive, medical, and military uses where devices must operate over a wide range of temperatures, which require low failure rates. Toshiba has produced LEDs with an operating temperature range of −40 to 100 °C, which suits the LEDs for both indoor and outdoor use in applications such as lamps, ceiling lighting, street lights, and floodlights. [107]

  • Voltage sensitivity: LEDs must be supplied with a voltage above their threshold voltage and a current below their rating. Current and lifetime change greatly with a small change in applied voltage. They thus require a current-regulated supply (usually just a series resistor for indicator LEDs). [149]

  • Color rendition: Most cool- white LEDs have spectra that differ significantly from a black body radiator like the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can cause the color of objects to be perceived differently under cool-white LED illumination than sunlight or incandescent sources, due to metamerism , [150] red surfaces being rendered particularly poorly by typical phosphor-based cool-white LEDs.

  • Area light source: Single LEDs do not approximate a point source of light giving a spherical light distribution, but rather a lambertian distribution. So LEDs are difficult to apply to uses needing a spherical light field; however, different fields of light can be manipulated by the application of different optics or "lenses". LEDs cannot provide divergence below a few degrees. In contrast, lasers can emit beams with divergences of 0.2 degrees or less. [151]

  • Electrical polarity : Unlike incandescent light bulbs, which illuminate regardless of the electrical polarity , LEDs will only light with correct electrical polarity. To automatically match source polarity to LED devices, rectifiers can be used.

  • Blue hazard: There is a concern that blue LEDs and cool-white LEDs are now capable of exceeding safe limits of the so-called blue-light hazard as defined in eye safety specifications such as ANSI/IESNA RP-27.1–05: Recommended Practice for Photobiological Safety for Lamp and Lamp Systems. [152] [153]

  • Light pollution : Because white LEDs , especially those with high color temperature , emit much more short wavelength light than conventional outdoor light sources such as high-pressure sodium vapor lamps , the increased blue and green sensitivity of scotopic vision means that white LEDs used in outdoor lighting cause substantially more sky glow . [132] [154] [155] [156] [157] The American Medical Association warned on the use of high blue content white LEDs in street lighting, due to their higher impact on human health and environment, compared to low blue content light sources (eg High-Pressure Sodium, PC amber LEDs, and low CCT LEDs). [158]

  • Efficiency droop : The efficiency of LEDs decreases as the electric current increases. Heating also increases with higher currents which compromises the lifetime of the LED. These effects put practical limits on the current through an LED in high power applications. [62] [64] [65] [159]

  • Impact on insects: LEDs are much more attractive to insects than sodium-vapor lights, so much so that there has been speculative concern about the possibility of disruption to food webs. [160] [161]

  • Use in winter conditions: Since they do not give off much heat in comparison to incandescent lights, LED lights used for traffic control can have snow obscuring them, leading to accidents. [162] [163]

Applications [ edit ]

LED uses fall into four major categories:

  • Visual signals where light goes more or less directly from the source to the human eye, to convey a message or meaning

  • Illumination where light is reflected from objects to give visual response of these objects

  • Measuring and interacting with processes involving no human vision [164]

  • Narrow band light sensors where LEDs operate in a reverse-bias mode and respond to incident light, instead of emitting light [165] [166] [167] [168]

Indicators and signs [ edit ]

The low energy consumption , low maintenance and small size of LEDs has led to uses as status indicators and displays on a variety of equipment and installations. Large-area LED displays are used as stadium displays, dynamic decorative displays, and dynamic message signs on freeways. Thin, lightweight message displays are used at airports and railway stations, and as destination displays for trains, buses, trams, and ferries.

Red and green LED traffic signals

One-color light is well suited for traffic lights and signals, exit signs , emergency vehicle lighting , ships' navigation lights or lanterns (chromacity and luminance standards being set under the Convention on the International Regulations for Preventing Collisions at Sea 1972, Annex I and the CIE) and LED-based Christmas lights . In cold climates, LED traffic lights may remain snow-covered. [169] Red or yellow LEDs are used in indicator and alphanumeric displays in environments where night vision must be retained: aircraft cockpits, submarine and ship bridges, astronomy observatories, and in the field, eg night time animal watching and military field use.

Automotive applications for LEDs continue to grow.

Because of their long life, fast switching times, and their ability to be seen in broad daylight due to their high output and focus, LEDs have been used in brake lights for cars' high-mounted brake lights , trucks, and buses, and in turn signals for some time, but many vehicles now use LEDs for their rear light clusters. The use in brakes improves safety, due to a great reduction in the time needed to light fully, or faster rise time, up to 0.5 second faster [ citation needed ] than an incandescent bulb. This gives drivers behind more time to react. In a dual intensity circuit (rear markers and brakes) if the LEDs are not pulsed at a fast enough frequency, they can create a phantom array , where ghost images of the LED will appear if the eyes quickly scan across the array. White LED headlamps are starting to be used. Using LEDs has styling advantages because LEDs can form much thinner lights than incandescent lamps with parabolic reflectors .

Due to the relative cheapness of low output LEDs, they are also used in many temporary uses such as glowsticks , throwies , and the photonic textile Lumalive . Artists have also used LEDs for LED art .

Weather and all-hazards radio receivers with Specific Area Message Encoding (SAME) have three LEDs: red for warnings, orange for watches, and yellow for advisories and statements whenever issued.

Lighting [ edit ]

With the development of high-efficiency and high-power LEDs, it has become possible to use LEDs in lighting and illumination. To encourage the shift to LED lamps and other high-efficiency lighting, the US Department of Energy has created the L Prize competition. The Philips Lighting North America LED bulb won the first competition on August 3, 2011, after successfully completing 18 months of intensive field, lab, and product testing. [170]

LEDs are used as street lights and in other architectural lighting . The mechanical robustness and long lifetime are used in automotive lighting on cars, motorcycles, and bicycle lights . LED light emission may be efficiently controlled by using nonimaging optics principles.

LED street lights are employed on poles and in parking garages. In 2007, the Italian village of Torraca was the first place to convert its entire illumination system to LEDs. [171]

LEDs are used in aviation lighting. Airbus has used LED lighting in its Airbus A320 Enhanced since 2007, and Boeing uses LED lighting in the 787 . LEDs are also being used now in airport and heliport lighting. LED airport fixtures currently include medium-intensity runway lights, runway centerline lights, taxiway centerline and edge lights, guidance signs, and obstruction lighting.

LEDs are also used as a light source for DLP projectors, and to backlight LCD televisions (referred to as LED TVs ) and laptop displays. RGB LEDs raise the color gamut by as much as 45%. Screens for TV and computer displays can be made thinner using LEDs for backlighting. [172]

The lack of IR or heat radiation makes LEDs ideal for stage lights using banks of RGB LEDs that can easily change color and decrease heating from traditional stage lighting, as well as medical lighting where IR-radiation can be harmful. In energy conservation, the lower heat output of LEDs also means air conditioning (cooling) systems have less heat in need of disposal.

LEDs are small, durable and need little power, so they are used in handheld devices such as flashlights . LED strobe lights or camera flashes operate at a safe, low voltage, instead of the 250+ volts commonly found in xenon flashlamp-based lighting. This is especially useful in cameras on mobile phones , where space is at a premium and bulky voltage-raising circuitry is undesirable.

LEDs are used for infrared illumination in night vision uses including security cameras . A ring of LEDs around a video camera , aimed forward into a retroreflective background , allows chroma keying in video productions .

LED to be used for miners, to increase visibility inside mines

LEDs are used in mining operations , as cap lamps to provide light for miners. Research has been done to improve LEDs for mining, to reduce glare and to increase illumination, reducing risk of injury to the miners. [173]

LEDs are now used commonly in all market areas from commercial to home use: standard lighting, AV, stage, theatrical, architectural, and public installations, and wherever artificial light is used.

LEDs are increasingly finding uses in medical and educational applications, for example as mood enhancement, [ citation needed ] and new technologies such as AmBX , exploiting LED versatility. NASA has even sponsored research for the use of LEDs to promote health for astronauts. [174]

Data communication and other signalling [ edit ]

See also: Li-Fi

Light can be used to transmit data and analog signals. For example, lighting white LEDs can be used in systems assisting people to navigate in closed spaces while searching necessary rooms or objects. [175]

Assistive listening devices in many theaters and similar spaces use arrays of infrared LEDs to send sound to listeners' receivers. Light-emitting diodes (as well as semiconductor lasers) are used to send data over many types of fiber optic cable, from digital audio over TOSLINK cables to the very high bandwidth fiber links that form the Internet backbone. For some time, computers were commonly equipped with IrDA interfaces, which allowed them to send and receive data to nearby machines via infrared.

Because LEDs can cycle on and off millions of times per second, very high data bandwidth can be achieved. [176]

Sustainable lighting [ edit ]

Efficient lighting is needed for sustainable architecture . In 2009, US Department of Energy testing results on LED lamps showed an average efficacy of 35 lm/W, below that of typical CFLs , and as low as 9 lm/W, worse than standard incandescent bulbs. A typical 13-watt LED lamp emitted 450 to 650 lumens, [177] which is equivalent to a standard 40-watt incandescent bulb.

However, as of 2011, there are LED bulbs available as efficient as 150 lm/W and even inexpensive low-end models typically exceed 50 lm/W, so that a 6-watt LED could achieve the same results as a standard 40-watt incandescent bulb. The latter has an expected lifespan of 1,000 hours, whereas an LED can continue to operate with reduced efficiency for more than 50,000 hours.

See the chart below for a comparison of common light types:


LED CFL Incandescent
Lightbulb Projected Lifespan 50,000 teev 10,000 teev 1,200 hours
Watts Per Bulb (equiv. 60 watts) 10 14 60
Cost Per Bulb $2.00 $7.00 $1.25
KWh of Electricity Used Over 50,000 Hours 500 700 3000
Cost of Electricity (@ 0.10 per KWh) $50 $70 $300
Bulbs Needed for 50,000 Hours of Use 1 5 42
Equivalent 50,000 Hours Bulb Expense $2.00 $35.00 $52.50
TOTAL Cost for 50,000 Hours $52.00 $105.00 $352.50

Energy consumption [ edit ]

In the US, one kilowatt-hour (3.6 MJ) of electricity currently causes an average 1.34 pounds (610 g) of CO
2
emission. [178] Assuming the average light bulb is on for 10 hours a day, a 40-watt bulb will cause 196 pounds (89 kg) of CO
2
emission per year. The 6-watt LED equivalent will only cause 30 pounds (14 kg) of CO
2
over the same time span. A building's carbon footprint from lighting can, therefore, be reduced by 85% by exchanging all incandescent bulbs for new LEDs if a building previously used only incandescent bulbs.

In practice, most buildings that use a lot of lighting use fluorescent lighting , which has 22% luminous efficiency compared with 5% for filaments, so changing to LED lighting would still give a 34% reduction in electrical power use and carbon emissions.

The reduction in carbon emissions depends on the source of electricity. Nuclear power in the United States produced 19.2% of electricity in 2011, so reducing electricity consumption in the US reduces carbon emissions more than in France ( 75% nuclear electricity ) or Norway ( almost entirely hydroelectric ).

Replacing lights that spend the most time lit results in the most savings, so LED lights in infrequently used locations bring a smaller return on investment.

Light sources for machine vision systems [ edit ]

Machine vision systems often require bright and homogeneous illumination, so features of interest are easier to process. LEDs are often used for this purpose, and this is likely to remain one of their major uses until the price drops low enough to make signaling and illumination uses more widespread. Barcode scanners are the most common example of machine vision, and many low-cost products use red LEDs instead of lasers. [179] Optical computer mice are an example of LEDs in machine vision, as it is used to provide an even light source on the surface for the miniature camera within the mouse. LEDs constitute a nearly ideal light source for machine vision systems for several reasons:

  • The size of the illuminated field is usually comparatively small and machine vision systems are often quite expensive, so the cost of the light source is usually a minor concern. However, it might not be easy to replace a broken light source placed within complex machinery, and here the long service life of LEDs is a benefit.

  • LED elements tend to be small and can be placed with high density over flat or even-shaped substrates (PCBs etc.) so that bright and homogeneous sources that direct light from tightly controlled directions on inspected parts can be designed. This can often be obtained with small, low-cost lenses and diffusers, helping to achieve high light densities with control over lighting levels and homogeneity. LED sources can be shaped in several configurations (spot lights for reflective illumination; ring lights for coaxial illumination; backlights for contour illumination; linear assemblies; flat, large format panels; dome sources for diffused, omnidirectional illumination).

  • LEDs can be easily strobed (in the microsecond range and below) and synchronized with imaging. High-power LEDs are available allowing well-lit images even with very short light pulses. This is often used to obtain crisp and sharp "still" images of quickly moving parts.

  • LEDs come in several different colors and wavelengths, allowing easy use of the best color for each need, where different color may provide better visibility of features of interest. Having a precisely known spectrum allows tightly matched filters to be used to separate informative bandwidth or to reduce disturbing effects of ambient light. LEDs usually operate at comparatively low working temperatures, simplifying heat management, and dissipation. This allows using plastic lenses, filters, and diffusers. Waterproof units can also easily be designed, allowing use in harsh or wet environments (food, beverage, oil industries). [179]

Other applications [ edit ]

LED costume for stage performers

LED wallpaper by Meystyle

The light from LEDs can be modulated very quickly so they are used extensively in optical fiber and free space optics communications. This includes remote controls , such as for TVs, VCRs, and LED Computers, where infrared LEDs are often used. Opto-isolators use an LED combined with a photodiode or phototransistor to provide a signal path with electrical isolation between two circuits. This is especially useful in medical equipment where the signals from a low-voltage sensor circuit (usually battery-powered) in contact with a living organism must be electrically isolated from any possible electrical failure in a recording or monitoring device operating at potentially dangerous voltages. An optoisolator also allows information to be transferred between circuits not sharing a common ground potential.

Many sensor systems rely on light as the signal source. LEDs are often ideal as a light source due to the requirements of the sensors. LEDs are used as motion sensors , for example in optical computer mice . The Nintendo Wii 's sensor bar uses infrared LEDs. Pulse oximeters use them for measuring oxygen saturation . Some flatbed scanners use arrays of RGB LEDs rather than the typical cold-cathode fluorescent lamp as the light source. Having independent control of three illuminated colors allows the scanner to calibrate itself for more accurate color balance, and there is no need for warm-up. Further, its sensors only need be monochromatic, since at any one time the page being scanned is only lit by one color of light. Since LEDs can also be used as photodiodes, they can be used for both photo emission and detection. This could be used, for example, in a touchscreen that registers reflected light from a finger or stylus . [180] Many materials and biological systems are sensitive to, or dependent on, light. Grow lights use LEDs to increase photosynthesis in plants , [181] and bacteria and viruses can be removed from water and other substances using UV LEDs for sterilization . [98]

LEDs have also been used as a medium-quality voltage reference in electronic circuits. The forward voltage drop (eg about 1.7 V for a normal red LED) can be used instead of a Zener diode in low-voltage regulators. Red LEDs have the flattest I/V curve above the knee. Nitride-based LEDs have a fairly steep I/V curve and are useless for this purpose. Although LED forward voltage is far more current-dependent than a Zener diode, Zener diodes with breakdown voltages below 3 V are not widely available.

The progressive miniaturization of low-voltage lighting technology, such as LEDs and OLEDs , suitable to be incorporated into low-thickness materials has fostered in recent years the experimentation on combining light sources and wall covering surfaces to be applied onto interior walls. [182] The new possibilities offered by these developments have prompted some designers and companies, such as Meystyle , [183] Ingo Maurer , [184] Lomox [185] and Philips , [186] to research and develop proprietary LED wallpaper technologies, some of which are currently available for commercial purchase. Other solutions mainly exist as prototypes or are in the process of being further refined.