Bosh sahifa > Ko'rgazma > Kontent

Elektr quvvatini ishlab chiqaradigan elektrolit-changyutkichda yorug'lik emiruvchi diod (LED)

Apr 21, 2017

Nurli diod

Nurli diod
RBG-LED.jpg 5 mm keng tarqalgan holatda ko'k, yashil va qizil chiroqlar
Mehnat printsipi Electroluminescence
Ildirildi H._J._Round (1907) [1]
Oleg Losev (1927) [2]
Jeyms R. Biard (1961) [3]
Nik Holonyak (1962) [4]
Birinchi ishlab chiqarish 1962 yil oktyabr
Pinni sozlash Anote va katod
Elektron ramz
LED symbol.svg


An'anaviy LED qismlari. Epoksiyaning ichki qismi va pastki qismining tekis pastki qatlamlari zanjir sifatida ishlaydi, ular o'tkazuvchanlarni mexanik kuchlanish yoki tebranish orqali kuchli ravishda chiqarib yuborilishiga yo'l qo'ymaydi.











Asosiy E27 vintni bilan zamonaviy LED kuchaytirish


Lampochka shaklidagi, modernizatsiyalashtirilgan alyuminiy issiqlik batareyali yoritgichli , nurli diffuzli gumbazli va E27 vintzal bazasiga ega bo'lgan LED chiroq , tarmoq voltajida ishlaydigan ichki quvvat manbai yordamida




Yuzaki sirtini joylashtirish LEDni yaqin tasvir





Yoritgichli diod ( LED ) - ikkita qo'rg'oshin yarim o'tkazgichli yorug'lik manbai . U faollashtirilganda yorug'lik chiqaradigan p-n birikma diodi hisoblanadi . [5] Tarmoqlarga muvofiq kuchlanish qo'llanilganda elektronlar qurilmadagi elektron teshiklari bilan birlashib, fotonlar shaklida energiyani bo'shatadi. Ushbu ta'sir elektroluminesans deb ataladi va yorug'lik rangi (foton energiyasiga mos keladigan) yarimo'tkazgichning energiya bandining bo'shlig'i bilan belgilanadi. LEDlar odatda kichik (1 mm dan kam) va radiatsiyaviy naqshni shakllantirish uchun integrallashgan optik komponentlar mavjud bo'lishi mumkin. [6]

1962 yilda amaliy elektron komponentlar ko'rinishida [7] eng erta LEDlar quyosh qizg'in infraqizil nur chiqaradilar. Infraqizil LED-lashlar uzoqdan boshqariladigan kontaktlarning uzatuvchi elementlari sifatida tez-tez ishlatiladi, masalan, uzoqdan qo'mondon elektronikasi uchun. Birinchi ko'zga ko'rinadigan yoritgichlar ham past qizg'in va qizil rangga ega edi. Zamonaviy LEDlar juda yorqinligi bilan ko'rinadigan , ultrabinafsha va infraqizil to'lqin uzunliklarida mavjud.

Erta LEDlar ko'pincha kichik akkor lampalar o'rniga qo'yilgan elektron qurilmalar uchun yoritgichlar sifatida ishlatilgan. Ular yaqinda etti segmentli displey ko'rinishida soni o'qishga joylashtirilgan va odatda raqamli soatlarda ko'rishgan. LEDlardagi so'nggi o'zgarishlar ularga atrof-muhit va vazifalarni yoritishda foydalanish imkonini beradi. LEDlar yangi displeylar va sensorlarni ishlab chiqishga imkon berdi, ularning yuqori almashinuv stavkalari esa ilg'or aloqa texnologiyasida ham qo'llanilmoqda.

Chiroqlarning yorug'lik manbalari, shu jumladan past energiya iste'moli, umr muddati, jismoniy mustahkamligi, kattaligi va tezroq almashinuvi uchun LEDlar ko'p afzalliklarga ega. Yorituvchi diodlar hozirda aviatsiya yoritgichlari , avtomobillar faralari , reklama, umumiy yoritish , transport signallari , kamera yonib turishi va yoritilgan fon rasmi kabi turli xil ilovalarda qo'llaniladi. 2017 yildan boshlab, LED yoritgichlar uy xonasining yoritilishi mos keladigan chiqindilardan kompakt lyuminestsent chiroq manbalariga qaraganda arzon yoki arzonroqdir. [8] Ular, shuningdek, sezilarli darajada ko'proq energiya tejamli va, ehtimol, ularni yo'q qilish bilan bog'liq ekologik muammolarni kamaytiradi. [9] [10]


Mundarija

[ Yashirish ]


Tarix [ tahrir ]

Kashfiyotlar va dastlabki qurilmalar [ tahrir ]

SiC kristalida nuqta aloqasidan yashil elektrolokinatsiyalanish 1907 yildan boshlab Round eksperimentini qayta tiklaydi.

Elektromagnit inshoot 1907 yilda Marconi Labs kompaniyasining ingliz tajribachisi HJ Round tomonidan silikon karbid kristallarini va mushuk mo'ylovli detektori yordamida kashf etildi . [11] [12] Rossiyalik ixtirochi Oleg Losev 1927 yilda birinchi LEDni yaratishni e'lon qildi. [13] Uning tadqiqotlari sovet, nemis va ingliz ilmiy jurnallarida tarqatildi, biroq o'nlab yillar davomida kashfiyotdan amaliy foydalanilmadi. Kurt Lehovec , Karl Accardo va Eduard Jamgochian , bu birinchi yoritgichli diodlarni 1951-yilda SiC kristallarini oqim manbai yoki impuls generatori bilan ishlatadigan apparati va bir variant, toza, billur bilan taqqoslash bilan izohladi. (1953). [16] [17]

Amerikaning Radio Corporation of Rubin Braunstein [18] 1955 yilda gallium arsenidi (GaAs) va boshqa yarimo'tkazgich qotishmalaridan infraqizil emissiya haqida xabar berdi. [19] Braunstein gallium antimonidi (GaSb), GaAs, indiy Fosfit (InP) va silikon-germanyum (SiGe) qotishmalari va 77 Kelvin-da.

1957-yilda Braunshteyn qisqa masofaga radioaloqa aloqasi uchun ishlatilishi mumkinligini ko'rsatdi. Kraemer [20] Braunstein ta'kidlaganidek: "oddiy optik aloqa liniyasi qurilgan edi: GaAs diodasining ilgari tokini modulyatsiya qilish uchun tegishli elektronika orqali rekorddan o'ynagan musiqachidan chiqqan musiqa ishlatilgan, yoritilgan nur PbS diodi bilan aniqlandi Masofadan uzoqda bo'lgan bu uzatish ovozli kuchaytirgichga uzatildi va karnay yoqilgan edi, shovqinni to'xtatib, musiqani to'xtatdi, biz bu moslama bilan juda qiziqarli o'yin o'ynadik. " Ushbu qurilma optik aloqa ilovalari uchun LEDlarni ishlatishni boshlagan.

Texas Instruments SNX-100 GaAs LED TO-18 tranzistorli metall korpusida joylashgan.

1961 yil sentyabr oyida Dallas , Teksas , Dallas Texas Instruments'da ishlayotganda, Jeyms R. Biard va Gari Pittman GaAs substratida qurilgan tunnel diodasidan yaqin infraqizil (900 nm) yorug'lik emissiyasini topdilar. [7] 1961 yil oktyabrga qadar ular GaAs pn birlashma nuri yoritgichi va elektr izolyatsiyalangan yarimo'tkazgich fotodetektori o'rtasida samarali yorug'lik emissiya va signal uzatishni namoyish etdilar. 1962-yil 8-avgustda Biard va Pittman "Semi-Conductor Radiant Diode" deb nomlangan patentga asoslanib, ularning natijalariga asosan, sinkning diffuzli yorug'ligini samarali yoritish imkonini beruvchi armatura bilan katodli kontaktli pn -n birikmasi Oldinga siljish . GE Labs, RCA Research Labs, IBM Research Labs, Bell Labs va MITdagi Linkoln Lab laboratoriyasidan kelib chiqadigan texnik daftarlarga asoslangan o'zlarining ustuvorligini belgilab olgach, AQSh patent idorasi ikkita ixtiroga GaAs infraqizil (IR ) Birinchi amaliy LED yorug'lik chiqaradigan diyot (AQSh Patent US3293513 ). [7] Patent topshirilgandan so'ng, Texas Instruments (TI) infraqizil diyotlarni ishlab chiqarish bo'yicha loyihani boshladi. 1962 yilning oktyabrida TI 890 nm yorug'lik chiqaradigan sof GaAs kristalini ishlatadigan birinchi tijoratli LED mahsulotini (SNX-100) e'lon qildi. [7] 1963 yilning oktyabrida TI birinchi savdo yarimsherik yoritgichni, SNX-110 ni e'lon qildi. [22]

Birinchi ko'zga ko'rinadigan spektrli (qizil) LED 1962 yilda General Electric kompaniyasida ishlagan Nik Holonyak tomonidan ishlab chiqilgan. Holonyak 1962-yil 1-dekabrda Applied Physics Letters jurnalida o'zining LED-ni e'lon qildi. [23] [24] M. Jorj Craford , [25] sobiq Holonyak magistr talabasi birinchi sariq LEDni ixtiro qildi va qizil va 1972-yilda TP Pearsall optik tolali telekommunikatsiya uchun birinchi yuqori yorqinligi, yuqori samarali yorug'lik yoritgichlarini yaratdi va optik tolali to'lqin uzunliklariga mos ravishda yangi yarimo'tkazgich materiallarini ixtiro qildi. [27]

Dastlabki tijoriy rivojlanish [ tahrir ]

Birinchi tijoratli yoritgichlar, odatda, akkor va neon ko'rsatkich lampalar uchun almashtirilganda va yettita segmentli displeylarda [28] birinchi navbatda qimmatbaho asbob-uskunalarda, laboratoriya va elektronika sinov uskunalari, so'ngra televizor, radio, telefon, Hisoblagichlar, shuningdek, soatlar ( signallardan foydalanish ro'yxatiga qarang). 1968 yilgacha ko'zga ko'rinadigan va infraqizil LEDlar har bir birlik uchun 200 AQSh dollari miqdorida juda qimmatga tushdi va shuning uchun juda kam amaliy foydalanishga ega edi. [19] Monsanto kompaniyasi 1968 yilda gorizontal arsenid fosfit (GaAsP) dan foydalanib, ko'rsatkichlar uchun mos qizil LED ishlab chiqarish uchun ko'zga ko'rinadigan LEDlarni ommaviy ishlab chiqarish uchun birinchi tashkilotdir. [29] Hewlett Packard (HP) 1968 yilda dastlab Monsanto tomonidan taqdim etilgan GaAsP dan foydalangan holda LEDlarni taqdim etdi. Ushbu qizil chiroqlar faqat indikator sifatida foydalanish uchun etarlicha yorqin edi, chunki yorug'lik chiqishi hududni yoritib berish uchun yetarli emas edi. Kalkulyatorlardagi o'qishlar juda kichik edi, chunki ular o'qiydigan har bir raqamga plastik linzalar qurildi. Keyinchalik boshqa ranglar keng tarqalib, asbob-uskunalar va asbob-uskunalar paydo bo'ldi. 1970-yillarda Fairchild Optoelektronika tomonidan har biri besh sentdan kam bo'lgan tijoriy muvaffaqiyatli LED qurilmalari ishlab chiqarilgan. Ushbu qurilma Fairchild Semiconductor'da doktor Jan Hoerni tomonidan ixtiro qilingan planar jarayon bilan ishlab chiqarilgan murakkab yarim Supero'tkazuvchilar chiplarni ishlatgan. [30] [31] Chip ishlab chiqarish va innovatsion qadoqlash usullari uchun planar ishlov berishning kombinatsiyasi optoelektronika kashshofi Tomas Brandt boshchiligidagi Fairchildda zarur xarajatlarni kamaytirishga yordam berdi. [32] Ushbu usullar LED ishlab chiqaruvchilari tomonidan qo'llanib kelinmoqda. [33]

TI-30 ilmiy hisoblagichini (taxminan 1978) LED displeyi, ko'rinadigan raqam o'lchamini oshirish uchun plastik linzalarni ishlatadi

Ko'pgina LEDlar juda keng tarqalgan 5 mm T1¾ va 3 mm T1 paketlarida ishlab chiqilgan, ammo ko'tarilgan kuch chiqishi bilan ishonchlilikni saqlash uchun ortiqcha issiqlikni to'ldirish uchun tobora ko'proq zarur bo'lgan [34], bu esa yanada samarali kompleks paketlarni samarali issiqlik tarqalishiga moslashtirildi . Zamonaviy yuqori quvvatli LEDlar uchun paketlar erta LEDlarga juda o'xshashdir.

Moviy LED [ tahrir ]

Moviy LEDlar avval Herbert Paul Maruska tomonidan 1972 yilda RCA da safir substratda galyum nitridi (GaN) yordamida ishlab chiqilgan. [35] [36] SiC-lar ilk bor AQShda Krey tomonidan 1989 yilda sotilgan. [37] Biroq, bu birinchi ko'k LEDlarning hech biri juda yorqin edi.

Birinchi yuqori yorug'likli ko'k LED ni 1994 yilda Nichia Corporation shirkati Shuji Nakamura tomonidan namoyish etilgan va InGaN asosida ishlab chiqarilgan. Shu bilan birga, Nagoyadagi Isamu Akasaki va Xiroshi Amano sapfir substratlarida muhim GaN nukleaslanmasini ishlab chiqish va GaN ning p-turi dopingini namoyish etish ustida ishlashdi. Nakamura, Akasaki va Amano 2014 yilgi Nobel mukofoti bilan taqdirlandi. 1995 yilda Alberto Barbieri Kardiff Universiteti laboratoriyasida (GB) yuqori yorqin LEDlarning samaradorligi va ishonchliligini tekshirib chiqdi va (AlGaInP / GaAs) indiy kaltsiy oksidi (ITO) yordamida "shaffof aloqa" LEDini ko'rsatdi.

2001 yilda [41] va 2002 yillarda [42] silikonda galyum nitridi (GaN) nurlarini ko'paytirish bo'yicha ishlar muvaffaqiyatli namoyish etildi. 2012 yil yanvar oyida Osram savdo-sotiqda kremniyli substratlarda yetishtiriladigan yuqori quvvatli InGaN LED- larini namoyish etdi. [43]

Oq rangli yoritgichlar va yoritqichli yorug'lik [ tahrir ]

Moviy LEDlarning yuqori samaradorligiga erishish tezda birinchi oq LEDning rivojlanishi bilan kuzatildi. Ushbu qurilmada Y
3 Al
5 O
12 : Ce (" YAG " deb nomlanuvchi) emitgichga fosfor qoplamasi ko'k emissiyaning ba'zi qismlarini absorbe qiladi va flüoresans orqali sariq rangli nur hosil qiladi. Qolgan ko'k chiroqli sariq rangning kombinatsiyasi ko'zga oq ko'rinadi. Shu bilan birga, turli xil fosforlarni (lyuminestsent materiallar) ishlatish o'rniga, floresans orqali yashil va qizil chiroqlarni ishlab chiqarish mumkin bo'ldi. Olingan qizil, yashil va ko'k rangli aralash nafaqat odamlar oq nur sifatida algılanmakla bilan birga, rang berish uchun yorug'lik uchun ustundir, lekin faqat sariq (va qolgan ko'k) bilan yoritilgan qizil yoki yashil narsalarning rangi, YAG fosforidagi to'lqin uzunligi.

Haitz qonuni , yorug'likning yorug'lik chiqishi vaqtida yoritishni yaxshilashga ko'rsatma, vertikal o'qda logaritmik shkala bilan

Birinchi oq LEDlar qimmat va samarasiz edi. Biroq, LEDlarning yorug'lik chiqishi 1960-yillardan boshlab ( Moor qonuniga o'xshash) taxminan har 36 oyda ikki barobar ko'payib, chidamli ravishda oshdi. Bu tendentsiya, odatda, boshqa yarim o'tkazgichli texnologiyalarni va optika sohasidagi taraqqiyot va materialshunoslikning parallel rivojlanishi bilan bog'liq bo'lib, doktor Roland Haitsdan keyin Haiti qonuni deb ataladi. [44]

Ko'k va yaqin ultrabinafsha LEDlarning yorug'lik chiqishi va samaradorligi ishonchli qurilmalarning narxi tushganligi sababli ko'tarildi: bu yorug'lik va akkumulyatorli yoritish o'rnini bosadigan yorug'lik uchun yuqori quvvatli oq yorug'lik nurlarini ishlatishga olib keldi. [45] [46]

Tajribali oq rangli LEDlar bir barobar elektr uchun 300 lumen ishlab chiqarish uchun namoyish etilgan; Ba'zilari 100,000 soatgacha davom etishi mumkin. [44] Akkor lampochka bilan taqqoslaganda, bu elektr samaradorligining kattagina ortishi bilan emas, balki vaqt davomida - bir lampochka uchun o'xshash yoki past narx. [48]

Ish printsipi [ tahrir ]

LED (ichki) va tarmoqli diagrammasi (pastki)

PN birikmasi so'rilgan nur energiyasini mutanosib elektr oqimiga aylantirishi mumkin. Xuddi shu jarayon bu erda qayta tiklanadi (ya'ni, PN birikmasi elektr energiyasi qo'llanilganda yorug'lik chiqaradi). Bu hodisa odatda elektroluminesans deb ataladi va bu elektromagnit maydon ta'sirida yarim o'tkazgichdan yorug'lik emissiyasi deb ta'riflanishi mumkin. Zaryadlovchilar elektronlar N-mintaqasidan kesib o'tib, P-mintaqasida mavjud bo'lgan teshiklarni birlashtirib, oldinga yo'naltirilgan PN birikmalarida birlashadilar. Erkin elektronlar energetik darajadagi o'tkazuvchanlik bandlarida , teshiklari esa valentlik energiya bandligida bo'ladi . Shunday qilib, teshiklarning energiya darajasi elektronlarning energiya darajasidan kamroq bo'ladi. Elektr va teshiklarni birlashtirish uchun energiyaning bir qismini tarqatish kerak. Bu energiya issiqlik va yorug'lik shaklida chiqariladi.

Elektronlar kremniy va germaniya diodlari uchun issiqlik shaklida energiyani yo'qotadi, ammo galyum arsenid fosfit (GaAsP) va gallium fosfit (GaP) yarimo'tkazgichlarida elektronni energiyani fotonlarni chiqarib yuboradi. Yarim Supero'tkazuvchi yarim Shaffof bo'lsa, u yoqilg'ining yorug'lik manbai bo'lib, yorug'lik chiqaradigan diodga aylanadi, lekin birlashma teskari tomonda bo'lsa LED bilan yorug'lik chiqarilmaydi va potentsial yetarli bo'lsa, Qurilma zarar etkazilishi mumkin.

Texnologiya [ tahrir ]

Diodning IV diagrammasi. 2 yoki 3 volttan ortiq kuch ishlatilganda, LED yoritishni boshlaydi. Orqaga noodatiy hudud old oqim mintaqasidan turli xil vertikal o'lchovni ishlatadi, bu holda oqish oqimi buzilib ketgunga qadar voltajning deyarli o'zgarmasligini ko'rsatishi mumkin. Oldinga chidamlilikda oqim kichikdir, lekin kuchlanish bilan chidamli kuchlanadi.

Fizika [ tahrir ]

LED lampochkaning birlashuvini hosil qilish uchun ifloslantiruvchi yarimo'tkazuvchi materialning chipidan iborat. Boshqa diodalarda bo'lgani kabi, oqim p-yonidan yoki anoddan n-yon yoki katodga osongina kiradi, lekin teskari yo'nalishda emas. Zaryadlovchi- elektronlar va teshiklar turli keskinlikdagi elektrodlardan kesishadi. Agar elektron elektron teshikka ega bo'lsa, u past energiya darajasiga tushadi va foton shaklida energiyani chiqaradi.

Yorug'likning to'lqin uzunligi va shu sababli uning rangi pn birikmasini tashkil etuvchi materiallarning tarmoqli bo'shlig'ining energiyasiga bog'liq. Kremniy va germaniya diodalarida elektronlar va teshiklar odatda radiatsion bo'lmagan o'tish yo'li bilan qayta ishlanadi , bu ular hech qanday optik emissiya hosil qilmaydi, chunki ular bevosita tarmoqli bo'shliq materiallari. LED uchun ishlatiladigan materiallar yaqin infraqizil, ko'rinadigan yoki ultrabinafsha nurga to'g'ri keladigan energiya bilan bevosita tarmoqli bo'sh joyga ega.

LED ishlab chiqarish infuzarali va qizil asboblar bilan gallium arsenidi bilan boshlangan . Materialshunoslik sohasidagi taraqqiyotlar, asboblarni har xil ranglarda yorug'lik chiqaradigan, har qachongidan uzunroq to'lqinlar bilan jihozlash imkonini berdi.

LEDlar, odatda, n-tipdagi substrat ustiga quriladi, uning elektrodi uning sirtiga biriktirilgan p-tipli qatlamga biriktiriladi. P-tipli substratlar, kamroq tarqalgan bo'lsa ham, yuzaga keladi. Ko'p tijoriy LEDlar, ayniqsa GaN / InGaN, shuningdek safir substratdan ham foydalanishadi.

Sinov indekslari [ tahrir ]

Yagona nuqta manbai emissiya zonasi uchun oddiy kvadrat yarim o'tkazgichda yorug'lik emissiya kon'yuslarining ideal namunasi. Chapdagi rasm shaffof gofreka uchun, o'ng chizilgan quyi qatlam shaffof bo'lganda tashkil topgan yarim konuslarni ko'rsatadi. Yorug'lik, aslida nuqta-manbadan barcha yo'nalishlarda teng ravishda chiqariladi, lekin faqat yarim Supero'tkazuvchilar yuzasiga perpendikulyar va konus shakllari bilan tasvirlangan tomonga bir daraja tegishi mumkin. Tanqidiy burchagidan oshib ketganda, fotonlar ichki ko'rinishda namoyon bo'ladi. Konuslar orasidagi joylar issiqlik sifatida bekor qilingan yorug'lik energiyasini ifodalaydi. [49] LED ishlab chiqarishda ishlatiladigan materiallarning aksariyati juda yuqori refraktiv ko'rsatkichlarga ega . Bu shuni anglatadiki, nurning aksariyati material / havo sirt interfeysi materialiga qaytariladi. Shunday qilib, LED'lardagi nurni olish juda ko'p izlanishlar va ishlab chiqilgan LED ishlab chiqarishning muhim jihatlaridan biridir. Haqiqiy LED gofrekasining yorug'lik emissiya konuslari bir nuqta manbai yorug'lik emissiyasidan ancha murakkab. Yorug'lik zonasi odatda gofretlar orasidagi ikki o'lchovli tekislikdir. Ushbu samolyot bo'ylab har bir atom bir xil emissiya konusiga ega. Miqdori bir-biriga bog'lab qo'yilgan konuslarni chizish mumkin emas, shuning uchun bu barcha emissiya kon'yunkalarini birlashtiradigan soddalashtirilgan diagrammasi. Katta kat konuslari ichki xususiyatlarni ko'rsatish va murakkablikni kamaytirish uchun kesilgan; Ular ikki o'lchamli emissiya tekisligining qarama-qarshi qirralariga uzayadi.

Yalang'och bo'lmagan yarimo'tkazgichlar, masalan, silikon ochiq havoga nisbatan juda yuqori parchalanish indeksini namoyon qiladi, bu esa butun ichki ichki aks etishi tufayli yarimo'tkazgichning havo bilan bog'laydigan yuzasiga nisbatan o'tkir burchaklarga o'tadigan fotonlarning o'tishini oldini oladi. Bu xususiyat LEDlarning yorug'lik emissiya samaradorligini hamda fotovoltaik kameralarning yorug'lik emiruvchanligi samaradorligini ham ta'sir qiladi. Kremniyning sinishi indikatori 3.96 (590 nm), [50] , havo esa 1.0002926 dir. [51]

Umuman olganda, tekis sirt qoplamaydigan LED yarim o'tkazgich chipi faqat yarim o'tkazgichning yuzasiga perpendikulyar yorug'lik chiqaradi va yorug'lik konusi , konusning yorug'ligi , yoki konus shaklida konus shaklida bir necha daraja tomonga chiqariladi [52] Koni . [49] Og'irlikning maksimal burchagi tanqidiy burchak deb ataladi. Ushbu burchagandan oshib ketganda, fotonlar yarim o'tkazgichdan qochib qutula olmaydi, aksincha yarimo'tkazgich kristalining ichkarisida xuddi oyna kabi aks ettiriladi. [49]

Ichki tasavvurlar boshqa kristalli yuzlardan qochishi mumkin, bunda insidens burchagi etarli darajada kam bo'lsa va kristal foton emissiyasini qayta emirmaslik uchun etarlicha shaffof bo'lsa. Biroq, har tomondan 90 graduslik burchakli sirtli oddiy kvadrat LED uchun barcha yuzlar teng burchakka neytronlar kabi harakat qiladi. Bunday holda nurning aksariyati qochib qutulolmaydi va kristalldagi chiqindi issiqlik kabi yo'qoladi. [49]

Tosh yoki fresnel linzalariga o'xshab burchak shaklidagi burchakli chakka sathlari foton emissiya nuqtalarining chetlariga qadar chip sirtiga perpendikulyar yorug'lik berish orqali yorug'lik chiqqani oshirishi mumkin. [53]

Yarim Supero'tkazuvchilar maksimal nurli chiqishi bilan ideal shakli aniq markazida yuzaga keladigan foton emissiyasi bilan mikrosfera bo'lib, elektrodlar markazga emissiya nuqtasi bilan aloqa qilish uchun kirib boradi. Markazdan kelib chiqqan barcha yorug'lik nurlari sohaning butun yuzasiga perpendikulyar bo'ladi, natijada ichki aks etmaydi. Yarimo'tkazuvchi yarim o'tkazgich ham, tekis yuzada, orqada tarqalgan fotonlar uchun bir oyna bo'lib xizmat qiladi. [54]

O'tish uchun qoplamalar [ tahrir ]

Gofretin dopingidan keyin u alohida o'limga bo'linadi. Har bir o'limga odatda chip deyiladi.

Ko'pgina LED yarimo'tkazgich chiplari aniq yoki rangli kalıplanmış plastmassa qobig'ida kapsüllenir yoki saksılar . Plastik qobiqning uchta maqsadi mavjud:

  1. Qurilmalardagi yarim o'tkazgich chipini o'rnatish osonroq.

  2. Kichik nozik elektr simlari jismonan qo'llab-quvvatlanadi va zararlanishdan himoyalangan.

  3. Plastik nisbatan yuqori indeksli yarimo'tkazgich va past indeksli ochiq havo orasidagi yorug'lik vositasi sifatida ishlaydi. [55]

Uchinchi xususiyat, yarim chastotali yoritgichni diffuzli linzalar vazifasini bajarish orqali yorug'lik emissiyasini kuchaytirishga yordam beradi, bu yalang'och yong'in faqat yorug'lik konusidan ko'ra yorug'lik konusidan ancha yuqori burchakka burilishga imkon beradi.

Faoliyat va operatsion ko'rsatkichlar [ tahrir ]

Odatda ko'rsatkich chiroqlari 30-60 MVt.dan oshiq elektr quvvati bilan ishlashga mo'ljallangan. 1999 yil mobaynida, Philips Lumileds bir vattda doimiy foydalanishga qodir bo'lgan quvvatli LEDlarni taqdim etdi. Ushbu LEDlar kattaroq kuch-quvvatlarni boshqarish uchun juda katta yarim Supero'tkazuvchilar kichkina kataklardan foydalanganlar. Bundan tashqari, yarimo'tkazgichlar izlari, LED qoldiqlaridan issiqlik chiqarishni ta'minlash uchun metall slyugalarga o'rnatildi.

LED-ga asoslangan yoritish manbalarining asosiy afzalliklaridan biri yuqori nurli ta'sirga ega . Oq rangli yoritgichlar tezda mos keladigan va standart akkor nurli tizimlarning samaradorligini bartaraf etdi. 2002-yilda Lumileds 5 vattli yorug'lik yoritgichlarini ishlab chiqargan. U 18-22 lyumen vatt (lm / Vt) yorug'lik samaradorligi bilan ta'minlangan. Taqqoslash uchun 60-100 vattlik an'anaviy lampochka 15 litr / Vt atrofida chiqadi va standart lyuminestsent lampalar 100 lm / Vtgacha chiqadi.

2012 yildan boshlab, Philips har rang uchun quyidagi samaradorlikka erishdi. [56] Effekt qiymatlari har bir elektr energiyasi uchun fizik nurining kuchini ko'rsatadi. Vt-vattning samaradorligi qiymati inson ko'zining xususiyatlarini o'z ichiga oladi va yorqinlik funktsiyasidan foydalaniladi .


Rang To'lqin uzunligi diapazoni (nm) Odatda samaradorlik koeffitsienti Odatda samaradorlik ( lm / Vt )

Qizil rangli 620 <>l <> 0.39 72

Qizil-to'q sariq 610 <>l <> 0.29 98

Yashil 520 <>l <> 0.15 93

Cyan 490 <>l <> 0.26 75

Moviy 460 <>l <> 0.35 37

2003 yil sentyabr oyida 20 miliamperda (mA) 24 mVtni iste'mol qilgan Cree tomonidan ko'k LEDning yangi turi namoyish etildi. Ushbu mahsulot 20 mA'da 65 lm / W ga teng bo'lgan, bozorda savdo sifatida taqdim etiladigan eng yorqin rangli va standart keragidan to'rt barobar ko'proq samarali oq rangli yorug'lik ishlab chiqaradi. 2006 yilda ular 20 mAda 131 lm / Vt yoritgichli oq rangli yorqinligi bilan prototip namoyish qildilar. Nichia korporatsiyasi 20 mA'lik ilgari oqimdagi 150 lm / Vt yorug'lik samaradorligi bilan oq rangli LED ishlab chiqardi. [57] 2011-yilda sotuvga chiqarilgan Cree XLamp XM-L LED'lari 10 Vt quvvatda 100 lm / Vt ishlab chiqarishi va taxminan 2 Vt kuchga ega bo'lganida 160 lm / Wgacha ishlab chiqaradi. 2012-yilda Kree 2014-yil mart oyida 254 lm / Vt, [58] va 303 lm / W ga teng bo'lgan oq LEDni e'lon qildi. [59] Amaliy umumiy yoritish kuchli quvvatli LEDlarga, bir vatt yoki undan ko'proqni talab qiladi. Bunday qurilmalar uchun odatiy ish oqimi 350 mAdan boshlanadi.

Ushbu samaralar faqat laboratoriyadagi past haroratda ushlab turiladigan nurli diyot uchun. Real armatura o'rnatilgan LEDlar yuqori haroratda ishlayotgani va haydovchining yo'qolishi bilan haqiqiy dunyo samaradorligi ancha past bo'ladi. Akkor chiroqlar yoki CFL o'rniga mo'ljallangan tijorat lampalar ishlab chiqarish bo'yicha AQSh Energetika boshqarmasi (DOE) 2009 yilda o'rtacha samaradorlik 46 lm / Vt bo'lganligini ko'rsatdi (test sinovlari 17 lm / W dan 79 lm / W gacha). [60]

Samaradorlik darajasi [ tahrir ]

Samarali ishlamaslik, LEDlarning yorug'lik samaradorligini pasayishi bo'lib, elektr toki o'nlab miliamperlardan oshib ketadi.

Ushbu ta'sir dastlab yuqori harorat bilan bog'liq bo'lishi kerak. Olimlar, buning aksi haqiqatni isbotladi: LEDning hayoti qisqartirilishi bilan birga, yuqori haroratda samaradorlik pasayishi ham kamroq. [61] 2007 yilda Auger rekombinatsiyasi sifatida samaradorlikni kamaytiruvchi mexanizm aniqlandi va u aralash reaktsiya bilan o'tdi. [62] 2013 yilda bir tadqiqot samaradorligi pasayishining sababi sifatida Auger rekombinatsiyasini tasdiqladi. [63]

Kamroq samarador bo'lishiga qaramay, yuqori oqimdagi ishlaydigan LEDlar LEDning ishlash muddatini buzadigan yuqori issiqlik darajasini yaratadi. Yuqori oqimlarda bu yuqori isitish tufayli yuqori rentabellikga ega yoritgichlar faqat 350 mA gacha ishlaydigan sanoat standartiga ega, bu yorug'lik chiqishi, samaradorligi va uzoq umrligi o'rtasidagi kelishmovchilikdir. [62] [64] [65] [66]

Mumkin bo'lgan echimlar [ tahrir ]

Hozirgi darajasini oshirish o'rniga, ko'p lampalarni bir lampochkada birlashtirish yo'li bilan yorqinlik ko'payadi. Faoliyatni kamaytirish muammosini hal qilish, uyda ishlaydigan LED lampochkalarni narxlarni sezilarli darajada kamaytiradigan kamroq LEDni talab qiladi.

AQSh dengiz tadqiqoti laboratoriyasining tadqiqotchilari rentabellik darajasini pasaytirish yo'lini topdilar. Eshituvchi vositalar AOK qilingan tashuvchilarning radiatsion bo'lmagan Auger rekombinatsiyasidan kelib chiqadi. Ular kvant quduqlarini yumshoq qamoqxona salohiyati bilan yaratdilar, ular radiatsion bo'lmagan Auger jarayonlarini kamaytirishdi. [67]

Tayvan Milliy Markaziy Universiteti va Epistar Corp tadqiqotchilari seramika alyuminiy nitridi (AlN) substratlarini qo'llash orqali samaradorlikni pasaytirish yo'lini ishlab chiqmoqdalar. Bular savdo sifatida ishlatiladigan safirga nisbatan ko'proq termal o'tkazuvchandir . Yuqori issiqlik o'tkazuvchanligi o'z-o'zidan isitish ta'sirini kamaytiradi. [68]

Lifetime va muvaffaqiyatsizlik [ tahrir ]

Asosiy maqola: LED yorug'lik rejimlari ro'yxati

Chiroqlar kabi qattiq holatda bo'lgan asboblar past oqimlarda va past haroratlarda ishlaydigan juda cheklangan aşınmaya va yıpranmaya bog'liq . Kundalik hayot muddati 25,000 dan 100,000 soatgacha bo'lgan, ammo issiqlik va joriy sozlamalar bu vaqtni sezilarli darajada qisqartirishi yoki qisqartirishi mumkin. [69]

LEDning eng ko'p uchraydigan alomati (va diodli lazer ) bu yorug'lik chiqishi va samaradorlikni yo'qotish asta-sekin kamayib boradi. Noyob bo'lsa-da, kutilmaganda muvaffaqiyatsizliklar ham yuz berishi mumkin. Erta qizil chiroqlar qisqa muddatli xizmat ko'rsatish muddati bilan ajralib turardi. Yuqori energiyali LEDlarning ishlab chiqarilishi bilan jihozlar an'anaviy qurilmalarga qaraganda yuqori aloqa harorati va yuqori oqim zichligi bilan ta'sirlanadi. Bu materialga stress tushishiga olib keladi va erta yorug'lik chiqindilarini buzilishiga olib kelishi mumkin. Foydali umrni standartlashtirilgan tarzda tasniflash uchun L70 yoki L50-ni ishlatish tavsiya etilgan, bu esa ma'lum bir yoritgichning o'zida navbati bilan 70% va boshlang'ich yorug'likning 50% ni tashkil etadigan ish vaqti (odatda minglab soatlarda beriladi). [70]

Ko'proq avvalgi yorug'lik manbalarida (akkor lampalar, deşarj lampalari va yonadigan yonilg'i, masalan, sham va yog 'chiroqlari) yorug'lik nurdan kelib chiqadi, ammo ular yetarli darajada salqin bo'lsa, ular ishlaydi. Ishlab chiqaruvchi odatda maksimal 125 yoki 150 ° C haroratni belgilaydi va past haroratlar uzoq umr ko'rish uchun tavsiya etiladi. Ushbu haroratlarda nisbatan kam issiqlik radiatsiya bilan yo'qoladi, ya'ni LED bilan hosil qilingan nur shamoli salqindir.

Yuqori quvvatli LEDda chiqadigan issiqlik (2015 yilga kelib iste'mol qilinadigan energiyaning yarmidan kam bo'lishi mumkin) LEDning substrati va to'plami orqali issiqlik qabul qilgichga o'tkaziladi , bu esa atrof-muhitga issiqlik beradi Konvektsiya orqali havo Shuning uchun ehtiyotkorlik bilan termal dizayni, LED paketining issiqlik qarshiligini , issiqlik batareyasini va ikkalasi orasidagi intervalni hisobga olgan holda zarur. O'rta kuch-quvvatli yoritgichlar tez-tez termal o'tkazuvchan metall qatlamni o'z ichiga olgan bosilgan elektron kartaga bevosita lehimlash uchun mo'ljallangan. Yuqori quvvatli LEDlar yuqori issiqlik o'tkazuvchanligi ( termal yog ' , o'zgarishlar o'zgaruvchan material , termal o'tkazuvchan yostiq yoki termal yopishtiruvchi ) bo'lgan material bo'lib, metallli issiqlik qabul qilgichiga biriktirilishi uchun mo'ljallangan katta maydonli keramik paketlarga paketlanadi.

Agar LED-asosidagi chiroq noto'g'ri o'rnatilgan armatura o'rnatilgan bo'lsa yoki armatura bepul havo aylanishiga ega bo'lmagan muhitda joylashgan bo'lsa, LEDni haddan tashqari qizib ketishi ehtimoldan holi bo'lib, hayotning qisqartirilishiga yoki erta katastrofik etishmovchilikka olib keladi. Termal dizayni odatda 25 ˚ C (77 ˚ F) atrof-muhit haroratiga asoslanadi. Ochiq ilovalarda, masalan, yo'l harakati signallari yoki svetofor signali chiroqlari va yorug'lik armaturasidagi harorat juda yuqori bo'lgan iqlim sharoitida ishlatiladigan LEDlar past rentabellikga ega yoki hatto kamchiliklarga duch kelishi mumkin. [71]

LED samaradorligi past haroratlarda yuqori bo'lgani sababli, LED texnologiyasi supermarket donduruculu yoritish uchun juda mos keladi. [72] [73] [74] LED'lar akkor chiroqlardan ko'ra kam chiqindi issiqlik hosil qilganligi sababli, muzlatgichlarda ularni ishlatish ham muzlatish xarajatlaridan qutqarishi mumkin. Biroq, sovuq va qor birikmalariga akkor chiroqlardan ko'ra sezgir bo'lishi mumkin [71], shuning uchun ba'zi LED yoritish tizimlari qo'shimcha isitish davri bilan yaratilgan. Bundan tashqari, izlanish chiroq ichida joylashgan issiqlikni yorug'lik moslamasining tegishli joylariga o'tkazadigan issiqlik chiqarish texnologiyalari ishlab chiqildi. [75]

Ranglar va materiallar [ tahrir ]

An'anaviy chiroqlar turli inorganik yarim o'tkazgich materiallaridan tayyorlanadi . Quyidagi jadval dalgaboyu diapazoni, kuchlanish pasayishi va materiallar mavjud ranglarini ko'rsatadi:


Rang To'lqin uzunligi [nm] Voltaj tushishi [DV] Yarıiletken material

Infraqizil L > 760 D V <> Galyum arsenidi (GaAs)
Alyuminiy galyum arsenidi (AlGaAs)

Qizil rangli 610 <>l <> 1.63 <>V V <> Alyuminiy galyum arsenidi (AlGaAs)
Galyum arsenid fosfidi (GaAsP)
Alyuminiy galyum indiy fosfidi (AlGaInP)
Galyum (III) fosfit (GaP)

apelsin 590 <>l <> 2.03 <>V V <> Galyum arsenid fosfidi (GaAsP)
Alyuminiy galyum indiy fosfidi (AlGaInP)
Galyum (III) fosfit (GaP)

Sariq 570 <>l <> 2.10 <>V V <> Galyum arsenid fosfidi (GaAsP)
Alyuminiy galyum indiy fosfidi (AlGaInP)
Galyum (III) fosfit (GaP)

Yashil 500 <>l <> 1.9 [76] <>V V <> An'anaviy yashil:
Galyum (III) fosfit (GaP)
Alyuminiy galyum indiy fosfidi (AlGaInP)
Alyuminiy galyum fosfidi (AlGaP)
Sof yashil:
Indium galyum nitriti (InGaN) / Galyum (III) nitrit (GaN)

Moviy 450 <>l <> 2.48 <>V V <> Sink selenid (ZnSe)
Indium galyum nitriti (InGaN)
Silikon karbid (SiC) substrat sifatida
Silikon (Si) substrat-ishlab chiqarishda

Violet 400 <>l <> 2.76 <>V V <> Indium galyum nitriti (InGaN)

Binafsha rang Ko'p turlari 2.48 <>V V <> Ikki ko'k / qizil chiroq,
Qizil fosforli ko'k,
Yoki binafsha rangli plastik bilan qoplangan

Ultraviyole L <> 3 <>V V <> Indium galyum nitriti (InGaN) (385-400 nm)

Olmos (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 to 210 nm [81]


Pink Multiple types Δ V ~ 3.3 [82] Blue with one or two phosphor layers,
yellow with red, orange or pink phosphor added afterwards,

white with pink plastic,
or white phosphors with pink pigment or dye over top. [83]


Oq rang Broad spectrum 2.8 < δ="">V <> Cool / Pure White: Blue/UV diode with yellow phosphor
Warm White: Blue diode with orange phosphor

Blue and ultraviolet [ edit ]

Blue LEDs

External video
Herb Maruska original blue LED College of New Jersey Sarnoff Collection.png
“The Original Blue LED” , Chemical Heritage 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]

Turlari [ tahrir ]

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 soat 10,000 soat 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.