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Svetleća dioda (LED), koja emituje svetlo kada se električno napajanje proizvodi elektroluminiscentom

Svetleća dioda (LED), koja emituje svetlo kada se električno napajanje proizvodi elektroluminiscentom

Apr 21, 2017

Svetlosna dioda

Svetlosna dioda
RBG-LED.jpg Plave, zelene i crvene LED diode u 5 mm difuznom kućištu
Radni princip Electroluminescence
Izneta H._J._Round (1907) [1]
Oleg Losev (1927) [2]
James R. Biard (1961) [3]
Nick Holonyak (1962) [4]
Prva proizvodnja Oktobar 1962
Pin konfiguracija Anoda i katoda
Elektronski simbol
LED symbol.svg


Delovi konvencionalne LED diode. Ravne donje površine nakovnja i posta ugrađene u epoksidni čin kao sidra, kako bi se spriječilo da se provodnici silom izvlače putem mehaničkog naprezanja ili vibracija.











Moderni LED retrofit sa E27 vijkom u bazi


Moderna retrofitna LED lampa u obliku sijalice sa aluminijumskim hladnjakom , svetlosnom difuznom kupolom i E27 vijcima , koristeći ugrađenu napojnu mrežu koja radi na mrežnom naponu




Zatvori sliku LED dioda na površini





Svetlosna dioda ( LED ) je dvoumni poluprovodnički izvor svetlosti . To je p-n spojna dioda , koja emituje svetlost kada se aktivira. [5] Kada se primeni odgovarajući napon na elektrode, elektroni se mogu rekombinirati sa elektronskim rupama unutar uređaja, oslobađajući energiju u obliku fotona . Ovaj efekat se naziva elektroluminescencija , a boja svetlosti (koja odgovara energiji fotona) određuje se energetskim pojasom poluprovodnika. LED diode su obično male (manje od 1 mm 2 ) i integrisane optičke komponente se mogu koristiti za oblikovanje dijagrama zračenja . [6]

Pojavljujući se kao praktične elektronske komponente 1962. godine, [7] najranije LED diode emitovale su infracrveno svjetlo niske intenziteta. Infracrvene LED diode se i dalje često koriste kao prenosni elementi u daljinskim upravljačkim krugovima, kao što su oni u daljinskim upravljačima za široku potrošnju elektronike. Prve LED diode vidljive svetlosti bile su takođe niske intenziteta i ograničene na crveno. Moderne LED diode su dostupne preko vidljivih , ultraljubičastih i infracrvenih talasnih dužina, sa veoma visokom osvetljenošću.

Rani LED diode su često korišćeni kao indikatorske lampe za elektronske uređaje, zamenjujući male sijalice. Ubrzo su bili upakovani u numeričke čitače u obliku sedam-segmentnih displeja i najčešće se vide u digitalnim satovima. Najnovija dostignuća LED-a omogućavaju im da se koriste u osvjetljavanju okoliša i zadataka. Svetleće diode su omogućile da se razviju novi ekrani i senzori, dok se njihova visoka brzina prebacivanja takođe koristi u naprednoj komunikacionoj tehnologiji.

LED diode imaju mnoge prednosti u odnosu na izvore svjetlosti koje uključuju nižu potrošnju energije, duži vijek trajanja, poboljšanu fizičku robusnost, manju veličinu i bržu promjenu. Svetleće diode se sada koriste u različitim aplikacijama kao što su vazduhoplovno osvetljenje , automatska farova , oglašavanje, opšte osvetljenje , saobraćajni signali , blic kamere i osvetljene pozadine. Od 2017. LED osvetljenje kućnih soba je jeftino ili jeftinije od kompaktnih fluorescentnih izvora sijaličnih izvora. [8] Takođe su značajno energetski efikasniji i, vjerovatno, imaju manje zabrinutosti za životnu sredinu vezanu za njihovo odlaganje. [9] [10]


Sadržaj

[ Sakrij ]


Istorija [ uredi ]

Otkrića i rani uređaji [ uredi ]

Zelena elektroluminescencija iz tačke kontakta na kristalu SiC-a ponovno osnaži prvobitni eksperiment Runde iz 1907. godine.

Electroluminescence kao fenomen otkrio je 1907. godine britanski eksperimentator HJ Round of Marconi Labs , koristeći kristal silicijum karbida i detektora mačaka . [11] [12] Ruski izumitelj Oleg Losev je izveštavao o stvaranju prve LED-a 1927. [13] Njegova istraživanja su distribuirana u sovjetskim, nemačkim i britanskim naučnim časopisima, ali praktična upotreba nije otkrivena već nekoliko decenija. [14] [15] Kurt Lehovec , Carl Accardo i Edward Jamgochian objasnili su ove prve svetlosne diode 1951. godine koristeći aparat koji koristi SiC kristale sa trenutnim izvorom baterija ili generatora pulsa i upoređivanjem sa varijantnom, čistom, kristalnom 1953. [16] [17]

Rubin Braunstein [18] Radio Corporation of America je objavio infracrvenu emisiju iz galijskog arsenida (GaAs) i drugih poluprovodničkih legura 1955. [19] Braunštajn je zapazio infracrvenu emisiju generisanu jednostavnim diode strukturama koristeći galijum antimonid (GaSb), GaAs, indijum Fosfidnih (InP) i legura silicijum-germanijuma (SiGe) na sobnoj temperaturi i na 77 Kelvina.

Godine 1957. Braunštajn je dalje pokazao da se osnovni uređaji mogu koristiti za ne-radio komunikaciju na kratkoj udaljenosti. Kao što je napomenuo Kroemer [20] Braunstein "... postavio je jednostavnu optičku komunikacionu vezu: Muzika koja se pojavila iz rekordera koristila je pomoću odgovarajuće elektronike za modulaciju naprijed struje GaAs diode. Emitovano svjetlo je detektovala PbS diodom neke Udaljavajući se od ovog signala, ušao je u audio pojačalo i reprodukovao ga zvučnik, a presretanje snopa je zaustavilo muziku i zabavljali smo se s ovom postavom. " Ova postavka predala je korištenje LED lampica za aplikacije optičke komunikacije.

Texas Instruments SNX-100 GaAs LED sadržan u TO-18 tranzistorski metalni kućištu.

U septembru 1961. godine, dok je radio na Texas Instruments- u u Dalasu u Teksasu , James R. Biard i Gary Pittman otkrili su blizu infracrvene (900 nm) emisije svetlosti iz tunelske diode koju su konstruisali na GaAs podlogu. [7] Do oktobra 1961. demonstrirali su efikasno emitovanje svjetla i signalno spajanje između GaAs pn spoja svjetlih emitera i električno izolovanog poluprovodničkog fotodetektora. [ 8 ] 8. augusta 1962. Biard i Pittman su podneli patent pod nazivom "Semiconductor Radiant Diode" na osnovu njihovih nalaza, u kojima je opisana LED dioda p-n spojnice cinka sa razmaknutim katodnim kontaktom kako bi se omogućilo efikasno emitovanje infracrvenog svjetla pod Napredna pristrasnost . Nakon utvrđivanja prioriteta njihovog rada zasnovan na inženjerskim notebook računarima koji su prethodili podnescima iz laboratorija GE Labs, RCA Research Labs, IBM Research Labs, Bell Labs i Lincoln Lab u MIT-u , američka patentna kancelarija izdala je dva izumitelja patentu za infracrvene GaAs (IR ) Dioda koja emituje svetlo (US patent US3293513 ), prva praktična LED dioda. [7] Odmah nakon podnošenja patenta, Texas Instruments (TI) započeo je projekat za proizvodnju infracrvenih dioda. U oktobru 1962. godine, TI je najavio prvi komercijalni LED proizvod (SNX-100), koji je koristio čist GaAs kristal da emituje 890 nm svjetlosti. [7] U oktobru 1963. TI je najavio prvu komercijalnu hemisferičku LED lampu, SNX-110. [22]

Prvi vidljivi spektar (crveni) LED je razvijen 1962. godine od strane Nick Holonyak, Jr. dok je radio u kompaniji General Electric . Holonyak je prvi put prijavio svoj LED u časopisu Applied Physics Letters 1. decembra 1962. [23] [24] M. George Craford , [25] bivši diplomirani student Holonyka, izumio je prvu žutu LED lampu i poboljšao osvetljenost crvenih i Crveno-narandžaste LED diode za faktor od deset u 1972. [26] 1976. godine TP Pearsall je stvorio prve visoke svjetlosti, visoko efikasne LED svjetiljke za optičke optičke vlakne izmišljajući nove poluprovodničke materijale posebno prilagođene talasnim dužinama prijenosa optičkih vlakana. [27]

Početni komercijalni razvoj [ uredi ]

Prve komercijalne LED diode su najčešće korišćene kao zamene za indikatorske lampice sa žaruljem i neonske signale, a na sedam-segmentnim displejima , prvo u skupoj opremi kao što su laboratorijska i elektronska oprema za testiranje, a kasnije u uređajima kao što su televizori, radio, telefoni, Kalkulatori, kao i satovi (vidi listu upotreba signala ). Do 1968. godine, vidljive i infracrvene LED diode su bile izuzetno skupe, po redosledu od 200 dolara po jedinici, i tako imala malo praktične upotrebe. [29] Kompanija Monsanto bila je prva organizacija koja je masovno proizvodila vidljive LED diode, koristeći galijum arzenid fosfid (GaAsP) 1968. godine za proizvodnju crvenih LED dioda pogodnih za indikatore. [29] Hewlett Packard (HP) je uveo LED diode 1968. godine, u početku je koristio GaAsP koji je isporučio Monsanto. Ove crvene LED diode su bile dovoljno svetle samo za upotrebu kao indikatori, jer izlaz svetla nije bio dovoljan da osvijetli područje. Otkrivanja u kalkulatorima su bila tako mala da su plastične sočiva napravljene preko svake cifre kako bi ih čitale. Kasnije su ostale boje postale dostupne i pojavile se u aparatima i opremi. U 1970-im su komercijalno uspešni LED uređaji sa manje od pet centi proizveli Fairchild Optoelectronics. Ovi uređaji su koristili složene poluprovodničke čipove proizvedene planarskim postupkom koji je izumio dr. Jean Hoerni na Fairchild Semiconductor . [30] [31] Kombinacija planarne obrade za izradu čipova i inovativnih metoda pakovanja omogućila je timu Fairchilda pod vođstvom optoelektronike pionir Thomas Brandt da postigne potrebno smanjenje troškova. [32] Ove metode i dalje koriste proizvođači LED. [33]

LED displej naučnog kalkulatora TI-30 (oko 1978), koji koristi plastične sočiva za povećanje veličine vidljive cifre

Većina LED dioda proizvedena je u veoma uobičajenim 5 mm T1¾ i 3 mm T1 paketom, ali sa rastućom izlaznom snagom, postaje sve veća potreba da se izbjegne višak toplote kako bi se održala pouzdanost [34], tako da su složeni paketi prilagođeni efikasnom disipaciji toplote . Paketi za najsavremenije LED visoke snage imaju malo sličnosti sa ranijim LED dioda.

Plava LED [ uredi ]

Plave LED diode su prvi put razvili Herbert Paul Maruska na RCA 1972. godine koristeći galijum-nitrid (GaN) na podlozi sapfira. [35] [36] SiC-tipovi su prvi put komercijalno prodati u Sjedinjenim Državama od strane Cree-a 1989. [37] Međutim, ni jedna od ovih inicijalnih plavih LED-a nije bila vrlo svetla.

Prvu visoku svjetlinu LED plave boje pokazala je Shuji Nakamura iz Nichia Corporation iz 1994. godine i zasnovana je na InGaN-u . [38] [39] Paralelno, Isamu Akasaki i Hiroshi Amano u Nagoji su radili na razvoju važne GaN nukleacije na safirnim podlogama i demonstraciji dopinga Ga -a tipa p-tipa . Nakamura, Akasaki i Amano dobili su Nobelovu nagradu za fiziku za svoj rad u 2014. godini . [40] Godine 1995. Alberto Barbieri na laboratoriji Univerziteta u Cardiffu (GB) istraživao je efikasnost i pouzdanost LED-a visokog osvetljenja i demonstrirao LED "transparentan kontakt" pomoću indijum-oksida (ITO) na (AlGaInP / GaAs).

Tokom 2001. godine [41] i 2002, [42] uspješno su prikazani procesi za povećanje LED dioda na galijum- nitridu (GaN) na silikonu . U januaru 2012. godine, Osram je demonstrirao visoke snage InGaN LED-a koje su rasle na silicijumskim podlogama komercijalno. [43]

Bela LED dioda i proboj osvetljenja [ uredi ]

Ostvarivanje visoke efikasnosti kod plavih LED-a brzo je pratilo razvoj prvog bijelog LED-a . U ovom uređaju je Y
3 Al
5 O
12 : Ce (poznat pod nazivom " YAG ") fosforni premaz na emiteru apsorbuje neke plave emisije i proizvodi žuto svetlo kroz fluorescenciju . Kombinacija tog žutog sa preostalim plavim svetlom pojavljuje se belo za oko. Međutim, korišćenjem različitih fosfora (fluorescentnih materijala) takođe je postalo moguće umjesto toga proizvesti zeleno i crveno svjetlo kroz fluorescenciju. Rezultujuća mešavina crvene, zelene i plave ne smatraju samo ljudima bela svetlost, već je superiorna za osvetljenje u smislu renderinga boja , dok ne možete da cenite boju crvenih ili zelenih predmeta osvetljenih samo žutom (i preostalom plavom bojom) Talasne dužine od YAG fosfora.

Ilustracija Haitzovog zakona , koja pokazuje poboljšanje izlaza svetlosti po LED-u tokom vremena, sa logaritamskom skalom na vertikalnoj osi

Prve bijele LED dioptrije bile su skupe i neefikasne. Međutim, svjetlosni izlaz LED-a povećao se eksponencijalno , uz udvostručenje koje se pojavilo otprilike svakih 36 mjeseci od 1960-ih (slično Mooreovom zakonu ). Ovaj trend se obično pripisuje paralelnom razvoju drugih poluprovodničkih tehnologija i napretku u optici i materijalnoj nauci i koji se zove Haitzov zakon nakon doktora Rolanda Haitza. [44]

Izlazna svetlost i efikasnost plavih i skoro ultraljubičastih LED dioda porasla je zahvaljujući smanjenom trošku pouzdanih uređaja: to je dovelo do upotrebe (relativno) LED visokih snaga bijelog svjetla u svrhu osvjetljenja koje zamjenjuju žarulju i fluorescentno osvjetljenje. [46] [46]

Pokazane su eksperimentalne bele LED diode da proizvode preko 300 lumena po vatu električne energije; Neki mogu trajati do 100.000 sati. [47] U poređenju sa sijalicama, ovo nije samo veliki porast električne efikasnosti, već - tokom vremena - sličan ili niži trošak po sijalici. [48]

Princip rada [ uredi - uredi ]

Unutrašnja radnja LED-a, koja pokazuje krug (gornji deo) i dijagram opsega (dno)

PN spoj može pretvoriti apsorbovanu svetlost u proporcionalnu električnu struju. Isti proces je ovde obrnut (tj. PN spoj emitira svetlost kada se električna energija nanosi na njega). Ova pojava se generalno naziva elektroluminiscenca , koja se može definisati kao emisija svetlosti iz poluvodnika pod uticajem električnog polja . Nosilci punjenja rekombiniraju se u predodređenom PN spoju kao elektroni koji pređu iz N-regiona i rekombiniraju se sa rupama koje postoje u P regionu. Slobodni elektroni su u provodnom pojasu nivoa energije, dok su rupe u valentnoj energiji . Tako će nivo energije rupe biti manji od nivoa energije elektrona. Neki dio energije mora biti raspršen kako bi se rekombinovali elektroni i rupice. Ova energija se emituje u obliku toplote i svetlosti.

Elektroni rasipaju energiju u vidu toplote za silikonske i germanijumske diode, ali u poluprovodnicima galij arsenid fosfida (GaAsP) i galijum fosfida (GaP), elektroni raspuštaju energiju emitovanjem fotona . Ako je poluprovodnik prozirni, spoj postaje izvor svetlosti u trenutku emitovanja, čime postaje dioda koja emituje svetlost, ali kada je spoj preokrenuti pristrasno, LED neće proizvesti svetlost, a ako je potencijal dovoljno velik, Uređaj će biti oštećen.

Tehnologija [ uredi ]

IV dijagram za diode . LED će početi emitovati svetlo kada se na njega primjenjuje više od 2 ili 3 volta. Region obrnutog predubavanja koristi drugu vertikalnu skalu iz regiona prednapregnute predispozicije, kako bi pokazao da je struja curenja gotovo konstantna sa naponom dok se ne dođe do kvara. U naprednoj pristrasnosti, struja je mala, ali se eksponencijalno povećava naponom.

Fizika [ uredi ]

LED se sastoji od čipa poluprovodnog materijala dopiranog nečistoćama za stvaranje pn spoja . Kao iu drugim diodama, struja lako protiče sa p-strane ili anode , na n-stranu ili katodu, ali ne u suprotnom smeru. Nosači punjenja - elektroni i rupe - prelaze u spoj od elektroda različitih napona. Kada elektron ispunjava rupu, pada u niži nivo energije i oslobađa energiju u obliku fotona .

Talinska dužina emitovane svetlosti, a time i njegova boja, zavisi od energije u pojasu materijala materijala koji formiraju pn spoj . U silikonskim ili germanijumskim diodama, elektroni i rupe se obično rekombiniraju ne-zračenjem , koja ne proizvodi optičku emisiju, jer su to indirektni pojasni materijali. Materijali koji se koriste za LED diode imaju direktnu pojasnu širinu s energijom koja odgovara infracrvenom, vidljivom ili skoro ultraljubičastom svjetlu.

LED razvoj je počeo sa infracrvenim i crvenim uređajima napravljenim sa galijum arsenidom . Napredak u nauci materijala omogućio je pravljenje uređaja sa sve kraćim talasnim dužinama, emitujući svetlost u različitim bojama.

LED diode se obično grade na n-tipu podloge, sa elektrodom pričvršćenom za sloj p-tipa koji se nanosi na površinu. Podloge tipa P, iako manje poznate, takođe se javljaju. Mnoge komercijalne LED diode, posebno GaN / InGaN, takođe koriste sapfirnu podlogu.

Indeks refrakcije [ uredi ]

Idealizovani primer emajliranja emulzije svetlosti u jednostavnom kvadratnom poluprovodniku, za jednu zonu emisije u tački izvora. Leva ilustracija je za providnu pločicu, dok na desnoj ilustraciji se prikazuju polu-konusi koji se formiraju kada je donji sloj neproziren. Svetlost se zapravo emituje jednako u svim pravcima od tačkastog izvora, ali može da se izbegne samo na površini poluprovodnika i nekoliko stepeni na stranu, što je ilustrovano oblikom konusa. Kada kritični ugao bude prekoračen, fotoni se reflektuju interno. Područja između čunjeva predstavljaju zarobljenu energiju svetlosti koja se troši kao toplota. [49] Većina materijala koji se koriste za proizvodnju LED proizvoda imaju vrlo visoke refraktivne indekse . To znači da će se većina svetlosti reflektovati natrag u materijal na interfejsu materijala materijala / zraka. Dakle, ekstrakcija svetlosti u LED-u je važan aspekt LED proizvodnje, pod velikim istraživanjem i razvojem. Smjernice za emitovanje svjetlosti stvarne LED vafel su daleko složenije od jedne emisije svjetlosti u tački izvora. Zona emisije svetlosti je tipično dvodimenzionalna ravnina između vafla. Svaki atom preko ovog aviona ima pojedinačni niz emisija kola. Crtež milijardi preklopnih stožnjaka je nemoguće, pa je ovo pojednostavljeni dijagram koji prikazuje razmake svih emisionih stožca u kombinaciji. Veći bočni stožci su obeleženi kako bi se pokazale unutrašnje karakteristike i smanjila složenost slika; Proširili bi se na suprotne ivice dvodimenzionalne emisijske ravni.

Goli nepromijenjeni poluprovodnici kao što je silicijum pokazuju veoma visok indeks refrakcije u odnosu na otvoreni zrak, što sprečava prolaz fotona koji dolaze u oštrim uglovima u odnosu na površinu poluprovodnika u kontaktu sa vazduhom usljed potpunog unutrašnjeg odraza . Ova svojstva utiču na efikasnost LED-a, kao i na efikasnost apsorpcije svetlosti fotonaponskih ćelija . Indeks refrakcije silicija je 3,96 (pri 590 nm), [50] dok je vazduh 1.0002926. [51]

U principu, LED poluprovodnički čip sa ravnim površinama ne emituje svetlost jedino pravolinijski na površinu poluprovodnika, a nekoliko stepeni u stranu, u obliku konusa označenog kao svetlosni konus , koeficijent svetlosti , [52] ili bekstvo Konus . [49] Maksimalni ugao incidencije naziva se kritični ugao . Kada se ovaj ugao prekorači, fotoni više ne izlaze iz poluprovodnika, već se umesto toga reflektuju unutra unutar poluprovodničkog kristala kao da je to ogledalo . [49]

Unutrašnja refleksija može pobjeći kroz druga kristalna lica ako je ugao incidencije dovoljno nizak i kristal dovoljno proziran da ne ponovo apsorbuje emisiju fotona. Ali za jednostavnu kvadratnu LED lampu sa uglovnim površinama sa 90 stepeni sa svih strana, lica se ponašaju kao ogledala jednakih uglova. U ovom slučaju, većina svetlosti ne može da pobegne i gubi se kao otpadna toplota u kristalu. [49]

Zaptivana površina čipa sa aneviranim fasetama sličnom draguljima ili fresnelovom sočivu može povećati izlaz svetlosti dozvoljavajući da se svetlost emituje okomito na površinu čipa, dok je daleko do strana tačke emisije fotona. [53]

Idealan oblik poluprovodnika sa maksimalnom izlaznom snagom bi bio mikrosfer sa emitovanjem fotona koji se javlja u tačno središtu, pri čemu se elektrode prodre u centar da bi se kontaktirale na tački emisije. Svi svetlosni zraci koji emituju iz centra bi bili pravolinijski na celu površinu sfere, što ne bi imalo unutrašnjih refleksija. Takođe bi radio hemisferički poluprovodnik, sa ravnom površinom koja služi kao ogledalo za fotonove koji se raširi. [54]

Tranzicioni premazi [ uredi ]

Posle dopinga vafla , razdvaja se na pojedinačne umake . Svaki umri se obično naziva čipom.

Mnogi LED poluprovodnički čipovi su inkapsulirani ili konusni u čistim ili obojenim plastificiranim školjkama. Plastična školjka ima tri namjene:

  1. Lakše je ostvariti montiranje poluprovodničkog čipa u uređaje.

  2. Mala nestabilna električna ožičenja su fizički podržana i zaštićena od oštećenja.

  3. Plastika deluje kao refraktivni posrednik između relativno visokog indeksnog poluprovodnika i nisko indeksnog otvorenog vazduha. [55]

Treća funkcija pomaže u povećanju emisije svetlosti iz poluprovodnika tako što djeluje kao difuzni objektiv, omogućavajući da se svjetlost emituje pri mnogo većem uglu incidencije od svjetlosnog konusa nego što golo čip može emitirati sam.

Efikasnost i operativni parametri [ uredi ]

Tipične LED indikatori su dizajnirani da rade sa ne više od 30-60 milliwatts (mW) električne energije. Oko 1999. godine, Philips Lumileds je uveo LED diode koje se mogu kontinuirano koristiti na jednom vatu . Ove LED diode su koristile mnogo veće veličine poluprovodnika za rukovanje velikim ulazima snage. Takođe, poluprovodničke matrice su postavljene na metalne puževe kako bi se omogućilo otklanjanje toplote od LED matrice.

Jedna od ključnih prednosti svetlosnih izvora LED-a je visoka svetlosna efikasnost . Bela LED dioda se brzo uskladila i prevazišla efikasnost standardnih sistema osvjetljenja. Lumileds je 2002. godine napravio LED diode sa pet vata sa svjetlosnom efektivnošću od 18-22 lumena po vatu (lm / W). Radi poređenja, konvencionalna sijalica od 60-100 vati emituje oko 15 lm / W, a standardna fluorescentna svetla emituju do 100 lm / W.

Od 2012. godine Philips je postigao sljedeće efikasnosti za svaku boju. [56] Vrednosti efikasnosti pokazuju fiziku - izlazna snaga po električnoj energiji. Vrednost efikasnosti lumena po vatu uključuje karakteristike ljudskog oka i izvedena je pomoću funkcije sjaja .


Boja Opseg talasnih dužina (nm) Tipični koeficijent efikasnosti Tipična efikasnost ( lm / W )

Crvena 620 <>λ <> 0.39 72

Crveno-narandžasta 610 <>λ <> 0.29 98

Zeleno 520 <>λ <> 0.15 93

Cijan 490 <>λ <> 0.26 75

Plava 460 <>λ <> 0.35 37

U septembru 2003. godine, Cree je demonstrirao novu vrstu plave LED diode, koji troši 24 mW na 20 mA (mA). Ovo je proizvelo komercijalno upakovano bijelo svjetlo dajući 65 lm / W pri 20 mA, postajući najsjajnija LED bijela koja je komercijalno dostupna u to vrijeme, a više od četiri puta efikasnija kao standardna rasvjeta. Tokom 2006. godine demonstrirali su prototip sa rekordno belom svetlosnom efektivnošću od 131 lm / W pri 20 mA. Nichia Corporation je razvio bijelu LED lampu sa svjetlosnom efikasnošću od 150 lm / W pri napojnoj struji od 20 mA. [57] Cree's XLamp XM-L LEDs, komercijalno dostupni u 2011. godini, proizvode 100 lm / W pri svojoj punoj snagu od 10 W i do 160 lm / W pri približno 2 W ulaznoj snazi. U 2012. godini, Cree najavio je beogradski LED dioda dajući 254 lm / W, [58] i 303 lm / W u martu 2014. [59] Za praktično opšte osvetljenje potrebna su LED dioda visoke snage od jedne vate ili više. Tipične radne struje za takve uređaje počinju od 350 mA.

Ove efikasnosti su samo za diode koja emituje svetlost, koja se drže na niskoj temperaturi u laboratoriji. S obzirom da LED-ovi ugrađeni u stvarne uređaje funkcionišu na višoj temperaturi i sa gubicima vozača, efikasnost u stvarnom svetu je znatno niža. Ispitivanje komercijalnih LED lampi dizajniranih za zamjenu svjetiljki sa žaruljem ili CFL-a u Sjedinjenim Američkim Državama pokazalo je da je prosječna efikasnost još uvijek iznosila 46 lm / W u 2009. godini (testirano je u rasponu od 17 lm / W do 79 lm / W). [60]

Efficiency droop [ uredi ]

Efikasnost je smanjenje svetlosne efikasnosti LED-a, dok se električna struja povećava iznad desetina milliampera.

Ovaj efekat je inicijalno teoretiziran da bude povezan sa povišenim temperaturama. Naučnici su dokazali suprotno da je istina: iako bi život LED-a bio skraćen, efekat padavine je manje izražen na povišenim temperaturama. [61] Mehanizam koji je izazvao smanjenje efikasnosti identifikovan je 2007. godine kao Auger rekombinacija , koja je uzeta sa mešovitom reakcijom. [62] U 2013, studija je potvrdila Augerovu rekombinaciju kao uzrok smanjenja efikasnosti. [63]

Pored toga što su manje efikasne, LED diode u većim električnim strujama stvaraju veće toplotne nivoe koji ugrožavaju životni vijek LED-a. Zbog ovog povećanog grejanja na višim strujama LED diode visoke osvetljenosti imaju industrijski standard koji radi samo na 350 mA, što predstavlja kompromis između izlaza svjetlosti, efikasnosti i dugovečnosti. [62] [64] [65] [66]

Moguća rešenja [ uredi ]

Umesto povećanja trenutnih nivoa, jačinu se obično povećava kombinovanjem više LED dioda u jednoj sijalici. Rešavanje problema smanjenja efikasnosti bi značilo da bi LED žarulje za domaćinstvo trebale manje LED-a, što bi značajno smanjilo troškove.

Istraživači Laboratorije za pomorsku istraživanje SAD pronašli su način smanjenja efikasnosti. Otkrili su da padavina proizlazi iz ne-radijatne Augerove rekombinacije injektiranih nosača. Oni su stvorili kvantne bunare sa mekim potencijalom za smanjenje ne-zračenja Auger procesa. [67]

Istraživači na Nacionalnom Centralnom univerzitetu u Tajvanu i Epistar Corp razvijaju način smanjenja efikasnosti zbog korištenja supstrata keramičkih aluminijum-nitrida (AlN), koji su toplije provodljivi od komercijalno korištenog safira. Veća toplotna provodljivost smanjuje efekte samo-grijanja. [68]

Lifetime and failure [ uredi ]

Glavni članak: Lista režima rada LED-a

Čvrsti uređaji kao što su LED diode su podložni veoma ograničenom habanju i suzbijanju ako se koriste na niskim strujama i na niskim temperaturama. Tipični vek trajanja je 25.000 do 100.000 sati, ali podešavanja toplote i struje mogu znatno proširiti ili skratiti ovaj put. [69]

Najčešći simptom otkaza LED (i diodnog lasera ) je postepeno smanjivanje izlaza i gubitak efikasnosti. Može se desiti i iznenadni otkazi, iako retki. Ranođe crvene LED diode su bile značajne za njihov kraći vek trajanja. Sa razvojem LED-a visoke snage, uređaji su podložni većim temperaturama preloma i većim gustinama struje od tradicionalnih uređaja. Ovo stvara stres na materijalu i može prouzrokovati degradaciju ranih svetlosnih izlaza. Da bi se kvantitativno klasifikovao korisni vek trajanja na standardizovan način, preporučeno je da se koriste L70 ili L50, koji su radni protokovi (tipično date u hiljadama sati), pri čemu dati LED dostiže 70% i 50% početnog izlaza svjetlosti, respektivno. [70]

Dok u većini prethodnih izvora svetlosti (žarulje sa žaruljem, sijalice za pražnjenje i one koje spaljuju zapaljivo gorivo, npr. Sveće i lampe ulja) svetlost je rezultat toplote, LED diode rade samo ako su dovoljno hladne. Proizvođač obično određuje maksimalnu temperaturu prelaza 125 ili 150 ° C, a niže temperature su poželjne u interesu dugog vijeka trajanja. Na ovim temperaturama, relativno mala toplota se gubi radijacijom, što znači da je svetlosni snop generisan LED-om ohlađen.

Otpadna toplota LED-a visoke snage (koja od 2015. može biti manja od polovine snage koju potroši) se prenosi pomoću podloge i paketa LED-a do hladnjaka , koji oslobađa toplotu do ambijenta Vazduh konvekcijom. Zato je pazljiv termički dizajn neophodan, uzimajući u obzir toplotne otpornosti LED-a, hladnjaka i interfejsa između njih. LED diode sa srednjom snagom često su projektovane tako da se direktno spajaju na štampanu ploču koja sadrži termički provodljiv metalni sloj. LED visoke snage se pakuju u keramičke pakete velikih površina dizajnirane da budu pričvršćene za metalni hladnjak , a interfejs je materijal sa visokom toplotnom provodljivošću ( termička mast , materijal za promjenu faze , termički provodnik ili termički lepak ).

Ako je svetiljka zasnovana na LED-u instalirana u neonvencionalnom svetiljku , ili se svetiljka nalazi u okruženju bez slobodnog cirkulacije vazduha, LED verovatno će se pregrijati, što rezultira smanjivanjem životnog veka ili ranim katastrofalnim otkazom. Termički dizajn se često zasniva na temperaturi okoline od 25 ° C (77 ° F). LED diode koje se koriste u vanjskim aplikacijama, kao što su saobraćajni signali ili signalna svetla u pločama, iu klimatskim uslovima gdje se temperatura u sklopu svjetlosti nalazi veoma visoka, može doživeti smanjenu izlaznu ili čak neuspjeh. [71]

Budući da je LED efikasnost veća na niskim temperaturama, LED tehnologija je pogodna za rasvjetu zamrzivača u supermarketu. [72] [73] [74] Zbog toga što LED dioda proizvodi manje otpadne toplote nego žarulje sa žarnom niti, njihova upotreba u zamrzivačima može štedeti i na troškovima rashlađivanja. Međutim, oni mogu biti više podložni nastanku mraza i snijega nego žarulje sa žaruljem, [71] tako da su neki LED sistemi osvjetljenja projektovani sa dodatnim grejnim krugom. Pored toga, istraživanje je razvilo tehnologije hladnjaka koje će prenijeti toplotu proizvedenu unutar spoja na odgovarajuća područja svjetlosnog uređaja. [75]

Boje i materijali [ uredi ]

Konvencionalne LED diode su iz različitih neorganskih poluprovodničkih materijala . Sledeća tabela prikazuje dostupne boje sa opsegom talasnih dužina, padom napona i materijala:


Boja Talasna dužina [nm] Pad napona [ΔV] Poluprovodnički materijal

Infracrvena Λ > 760 Δ V <> Galijum arsenid (GaAs)
Aluminijum galijum arsenid (AlGaAs)

Crvena 610 <>λ <> 1.63 <δ>V <> Aluminijum galijum arsenid (AlGaAs)
Galijum arzenid fosfid (GaAsP)
Aluminijum galijum indijum fosfid (AlGaInP)
Galijum (III) fosfid (GaP)

Narandžasta 590 <>λ <> 2.03 <δv><> Galijum arzenid fosfid (GaAsP)
Aluminijum galijum indijum fosfid (AlGaInP)
Galijum (III) fosfid (GaP)

Žuta 570 <>λ <> 2.10 <δv><> Galijum arzenid fosfid (GaAsP)
Aluminijum galijum indijum fosfid (AlGaInP)
Galijum (III) fosfid (GaP)

Zeleno 500 <>λ <> 1,9 [76] <δ>V <> Tradicionalno zeleno:
Galijum (III) fosfid (GaP)
Aluminijum galijum indijum fosfid (AlGaInP)
Aluminijum galijum fosfid (AlGaP)
Čisto zelena:
Indijum galijum-nitrid (InGaN) / galijum (III) nitrid (GaN)

Plava 450 <>λ <> 2.48 <δ>V <> Cink selenid (ZnSe)
Indijum galijum nitrid (InGaN)
Silicijum karbid (SiC) kao supstrat
Silicijum (Si) kao podloga u razvoju

Violet 400 <>λ <> 2.76 <δ>V <> Indijum galijum nitrid (InGaN)

Ljubičasta Višestruki tipovi 2.48 <δ>V <> Dvostruke plave / crvene LED diode,
Plava sa crvenim fosforom,
Ili bijela sa ljubičastom plastikom

Ultraviolet Λ <> 3 <δ>V <> Indijum galijum-nitrid (InGaN) (385-400 nm)

Dijamant (235 nm) [77]
Boron nitrid (215 nm) [78] [79]
Aluminijum nitrid (AlN) (210 nm) [80]
Aluminijum galijum-nitrid (AlGaN)
Aluminijum galijum-indijum-nitrid (AlGaInN) -nad na 210 nm [81]


Pink Višestruki tipovi Δ V ~ 3,3 [82] Plava sa jednim ili dva fosforna sloja,
Žuto sa crvenim, narandžastim ili roze fosforom, dodato nakon toga,

Bijela sa roze plastikom,
Ili bijelih fosfora sa ružičastim pigmentom ili bojom preko vrha. [83]


Beli Širokog spektra 2.8 <δ>V <> Cool / Pure White: plava / UV dioda sa žutim fosforom
Topla bela: plava dioda sa narandžastim fosforom

Plava i ultraljubičasta [ uredi - uredi ]

Plave LED diode

Vanjski video
Herb Maruska original plavi LED koledž u New Jerseyu Sarnoff Collection.png
"Originalna plava LED" , Fondacija za hemijsku baštinu

Prva plavo-ljubičasta LED dioda sa magnezijumom dopunjenog galijum-nitrida napravljena je na Univerzitetu Stanford 1972. godine od strane Herb Maruska i Wally Rhines, doktorskih studenata iz oblasti materijala i inženjerstva. [84] [85] U to doba Maruska je napustio RCA Laboratories , gdje je sarađivao sa Jacquesom Pankovejem na srodnom radu. 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]

Vrste [ uredi ]

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 hours 10.000 sati 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.