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Renewable and Sustainable Energy Reviews 51 (2015) 1-61

ht-emitting diodes' light qualities and their corresponding

ntific applications

hia Yeha, Ting Jou Dingb, Pulin Yehc1

of General Eduation! "ing#ao $niversity! %6& 'en-ua Road! eetou! C*ang*ua 52%+5! ,aiwan! RC b#e.art/ent of "aterials and

Engineering! "ing#ao $niversity %6& 'en-ua Road! eetou! C*ang*ua 52%+5! ,aiwan! RC #e.art/ent of nfor/ation "anage/ent!

3s $niversity! +&&! Se +! ,a/ 4ing Road! ,a/sui #istrit! ew ,ai.ei City! 251%5 ,aiwan! RC

T I C L EO

This paper reviews the studies that use LEDs based on their light qualities. The reviewed ields in!lude agri!ulture" aq

phototherap#" bio$edi!al resear!h" bio$ass produ!tion" and environ$ental appli!ations. The review leads to the !on!lu' the $ost versatile and ee!tive wavelengths are !entrali(ed in red" blue" and inrared seg$ents) %*' +, range LEgenerall# used or sterili(ation and disine!tion" are so$eti$es applied in bio$edi!al treat$ents. -ith the low power $aes long e/posure ne!essar# to indu!e signii!ant ee!t" +, LEDs are e/pe!ted to be used $ore widel# oina!tivation when their higher output versions are available) and %0' orange" #ellow" and green LEDs are less used as tlight sour!es e/!ept or being e$plo#ed in sensing devi!e. Nevertheless" green and #ellow LEDs are so$eti$es used the produ!tion or !ertain un!tions o non1!hloroph#ll based plants.

2 *3&4 Elsevier Ltd. All righ

Contents

u!tion45light qualities and their !orresponding appli!ations.................................................................................................................................................45Inrared and red %5031&333 n$'.....................................................................................................................................................................45

*.&.&. 7io$edi!al appli!ations......................................................................................................................................................................45

*.&.*. Agri!ulture and aqua!ulture................................................................................................................................................................45Orange" #ellow and green %43315*3 n$'......................................................................................................................................................................48*.*.&. 9ensing devi!e.....................................................................................................................................................................................48*.*.*. 7io$ass produ!tion and ish behavior stud#......................................................................................................................................4:

7lue %;431433 n$'........................................................................................................................................................................................................4:*.0.&.

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1( #ntroduction

LEDs" as generall# believed" are bright" !o$pa!t and long1 lasting.The# generate high light level with less heat and save on ele!tri!it#.The state1o1the1art white LED have rea!hed lu$inous ei!a!# oabout 033 l$=- at 043 $A & G at the orward voltage o about 0.&1;.3,. +nortunatel#" su!h LEDs6 best peror$an!e o!!urs onl# at lowinput power o &1&.4 -" whi!h $eans the total lu$inous output o alittle over 433 l$ at the top. The lu$inous ei!a!# o a good

luores!ent light !an rea!h &33 l$=-" whi!h $eans a *333 l$lu$inous output or a *3 - power input. For LEDs operated withinrated voltage" ei!ien!# droop %a drop in ei!a!# as the !urrent inputin!reases' !an drive the peror$an!e down to below &33 l$=- *G.For e/a$ple" an LED based on Ni!hia6s & $$ b# & $$ die thatdelivered &:0 l$=- at 043 $A drop to &03 l$=- at & A 0G. Currentl#"!o$bining $ultiple LEDs in one bulb to in!rease lu$inan!e is thesolution to avoid in!reasing the input !urrent.

Iveland et al. ;G have identiied the !ause o su!h ei!ien!# droopand resear!hers are beginning to !o$e up with possible solutions4"5G. 9olving the droop proble$ would signii!antl# redu!e !osts ohousehold LED light as ewer LEDs will be needed in ea!h bulb.+ntil then" LEDs powerul enough or general lighting are relativel#e/pensive and need better heat and !urrent $anage$ent than !o$pa!tluores!ent la$p o !o$parable lu$inan!e.

-hile not #et being e!ono$i!al enough to repla!e the luores!entlight or general lighting" LEDs" whi!h tri$ the need or the energ#that would have been wasted in irrelevant wavelengths" have long

being in good position to repla!e !onventional lights in s!ientii!resear!hes. This paper presents a brie develop$ent histor# o LEDs

b# !olors and reviews the resear!hes !ondu!ted under LED light odierent light qualities %na$el#" inrared" red" orange" green" #ellow"

blue" and ultraviolet' sin!e the dawn o high brightness LEDs.

)( LDs' light qualities and their corresponding applications

The !olors with their respe!tive wavelengths denoted in these!tions below are appro/i$ations sin!e the spe!tru$ is !ontinuouswithout obvious border line between the adBa!ent !olors.

*.&. nfrared and red (6%0-1000 n/)

The irst $odern LEDs" whi!h were patented in earl# &>53sH" wereinrared and red LEDs 8G" +ntil late &>53s" these LEDs were stillver# !ostl# and without $u!h pra!ti!al use :G. The irst !o$$er!ialLEDs were developed in late &>5* b# olon#a who !o$binedgalliu$" arseni! and phosphorus %JaAs

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:e* et al ; Renewable and Sustainable Energy Reviews 51 (2015) 55-61 %

Resear!hes that in!lude plant seedling" plant tissue !ulture andgrowth" in addition to spa!e agri!ulture *&G have shown that LEDshave be!o$e the $ainstrea$ light sour!e or the resear!hes in theagri!ultural ields.

-hile the pri$ar# light sour!e o the bio$edi!al and agri!ulturalstudies reviewed in this se!tion are IR LEDs" all these studies are not!ondu!ted with IR alone. Co$bining light sour!es o dierentwavelengths $a# help to dis!over the $ost avorable spe!tru$ $i/or a given purpose. For e/a$ple" red LEDs" while $i/ed with blue

ones" !an provide ee!tive" sae and non1painul treat$ent or $ild to$oderate a!ne **G"

A resear!h that !o$pared the growth o strawberr# plantlets underluores!ent and dierent blue=red LED ratios and irradiation levels*0G de$onstrated that a strawberr# plantlet !ulture s#ste$ using LEDis advantageous or the $i!ropropagation" the propagation o plantsvia !ultivating plantlets in tissue !ulture and then transplanting the$to their designated distinations. This stud# also veriied that the LEDlight sour!e or in vitro plantlet !ulture i$proved the growth o the

plants in adaptation. A stud# that evaluated the growth and dr# $atterpartitioning o Kungarian -a/ pepper plants grown under red LEDswith and without supple$ental blue or ar1red radiation indi!ated thatwith proper !o$bination o blue and ar1red wavelengths" red LEDs$a# be suitable or the !ulture o plants in tightl# !ontrolled environ1$ents *;G"

-ith the illu$ination as the $ost e/pensive a!tor o bio$assprodu!tion in a !losed photobiorea!tor" !ost1ee!tive te!hnologiesthat produ!e renewable energ# ro$ su!h bio$ass as algae and$i!roalgae !ontinuousl# e$erge. The superb photos#ntheti! !ap1abilities and avorable !arbon lie !#!le $ae algae" whi!h !an

produ!e lipids and h#dro!arbons rapidl#" a great alternative energ#sour!e. igh oil !ontent $i!roalgae !an be produ!ed in open ponds or!losed photobiorea!tors and are good sour!es or biouel produ!tion.

LEDs have opened new stud# perspe!tives on $odulating the!onversion o light energ# and the saturation o nutrient suppl#.atthiBs et al. have !ondu!ted a stud# that used LEDs o 54> n$ witha hal1power bandwidth o 03 n$ %whi!h is opti$al or e/!iting*loro.*ylls aand bin their red absorption bands' as the light sour!ein indoor !ulture o the green alga C*lorella .yrenoi- dosa The#de$onstrated that additional suppl# o blue light is not needed andthat using lashing LEDs in algal !ulture have resulted in a signii!antenerg# saving in !o$parison to lu$ines!ent light sour!es *4G.

-hile studies peror$ed under the light sour!e o a solewavelength help to identi# that wavelength6s inluen!e on !ertainappli!ations" resear!hes !ondu!ted under the !o$bination o various!olors $a# lead to the opti$i(ation o !ultivating ei!ien!# orunderstanding o so$e spe!ies6 light behavior patterns. A goode/a$ple !o$es ro$ a ish behavior stud# *5G that investigates thered" green" and blue LEDs6 ee!ts on o/idative stress in #ellowtail!lownish b# $easuring variet# o stress indi!ators. The stud# showedthat the e/pressions o those indi!ators are signii!antl# higher or thered spe!tra than those or the other light spe!tra. These results indi!atethat red light indu!es o/idative stress.

Tae algae produ!tion or e/a$ple" a resear!h that used LEDs

with various wavelengths and intensities to stud# the light ee!ts onthe S.irulina .latensis!ultivation de$onstrated that red LED indu!esthe highest spe!ii! growth rate and that blue LED is least ei!ient in

photon1to1bio$ass !onversion. The energ#1to1bio$ass ei!ien!#!o$parison result show that red LED is $ost e!ono$i!all# ei!ientor photoautotrophi! !ultivation *8G. Mo! et al. *:G re!o$$ended a

produ!tion s#ste$ that uses red lights irst or the desired !ell!on!entration and then swit!h to blue lights or !ell si(e based on theresults o their stud#" whi!h used red LEDs" blue LEDs" andluores!ent lights separatel# in a photobiorea!tor to grow C*lorella3 n$'" and green %4331 483n$' LEDs be!a$e available as the te!hnolog# progressed through the

&>83s. The irst #ellow LED was invented b# Craord 03G. TheseLEDs saw onl# a slight i$prove$ent in brightness and ei!ien!#during &>:3s as the basi! $aterial stru!ture re$ained relativel#un!hanged. Later use o laser diode te!hnolog# led to the develop$ento Indiu$ Jalliu$ Alu$inu$ 5 n$'" and phenol %833 n$'. -ith thisin !onsideration" photo$eters that dete!t dierent !he$i!als !an beor$ulated using LEDs o asso!iated spe!tru$ seg$ents and thusopen up new appli!ations or LEDs o less used !olor" su!h as #ellow.

ellow LEDs are so$eti$es used or ish spoilage $onitoring orba!teria !ultivation. 3 n$'overlaps well with the absorban!e spe!tru$ o the d#e6s basi! or$.For those who need to understand $ore about the !he$istr# andresponsivel# o d#e1 based p sensors" Leiner and -olbeis 0;G

provide detail des!ription.

222 8io/ass .rodution and fis* be*avior studyellow LEDs !an be put in good use or !arotenoid produ!tion

a!!ording to the result o a stud# that investigated the ee!ts o eightlight sour!es onR .alustrisgrowth and !arotenoid !ontent. -ith dar!ondition as the !ontrol" the eight light sour!es used are in!andes!ent"halogen" and luores!en!e la$ps in addition to white" #ellow" red"

blue" and green LEDs. The results show that #ellow LEDs !a$ese!ond to blue onl# in !arotenoid #ield 04G.

Jreen LEDs are so$eti$es used in ish behavior or bio$assprodu!tion resear!h as the light sour!e or the !ontrol groups in orderto !o$pare the peror$an!e o other light sour!es. Fish have adapted

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their $a/i$u$ photopig$ent sensitivit# a!!ording to theirunderwater photo environ$ents. 8& b# G. owever" the light output o those devi!eswas too little to be put in pra!ti!al use. Not until &>>; the high1

brightness blue LED" whi!h triggered signii!ant use o blue LEDs ins!ientii! appli!ations" was de$onstrated b# Naa$ura ;3G" Current

bright blue LEDs are based on the wide band gap se$i!ondu!torsindiu$ galliu$ nitride %InJaN ;431433 n$' and JaN %;43 n$'.

7lue light is probabl# the $ost widel# used or s!ientii!purposes. Its uses !over" a$ong other ields" the areas o bio$assprodu!tion %su!h as or algae growth and asta/anthin produ!tion';&";*G and aqua!ulture %su!h as ish larva develop$ent' ;0G" alongwith the !ulture o plants in !ontrolled environ$ents *;G"

The qualit# o the light1!uring unit %LC+' signii!antl# ae!ts theperor$an!e o dental !o$posites pol#$eri(ation. The outputs ohalogen LC+s tend to de!rease with ti$e and $a# !ause insui!ient$ono$er !onversion in dental !o$posites. In the dawn o high

brightness blue LEDs" dental !o$posite pol#$eri(ation studies ;;1;8G dis!overed that blue LED LC+s are $ore suitable or this

pol#$eri(ation tas as the# do not have su!h light de!reasingdrawba!s. The irradian!e o LED LC+s $a# be relativel# low" #etthe# are al$ost as ei!ient as the halogen units o twi!e theirradian!e.

9tahla et al. ;:G investigated the le/ural properties o three!o$posites with three shades via pol#$eri(ing ea!h with a!o$$er!ial halogen LC+ and an LED LC+" respe!tivel#. In $ost!ases no signii!ant dieren!es in le/ural strength and $odulus wasidentiied between !o$posites pol#$eri(ed with either unit.

2%1 *otoatalyst ativationLED is a pra!ti!able light sour!e to a!tivate the photo!atal#ti!

ee!ts o anatase titaniu$ dio/ide %Ti3*' in both reshwater andseawater a!!ording to a stud# !ondu!ted b# Cheng et al. ;>G" Theseresear!hers used blue LED a!tivated Ti3 *=Fe03;parti!les to evaluatethe parti!les6 photo!atal#ti! ei!ien!# and !on!luded that blue LEDshave si$ilar ee!t as +, light but !ause less har$ to hu$an e#es.

2%2 lant disease ontrol +sing LED arra#s o various !olor to stud# the light qualit#

ee!ts on the growth o to$ato $osai! virus in peppers and powder#$ildew on !u!u$bers" 9!huerger and 7rown 43G !on!luded that thequalit# o light $a# !hange the progress o plant disease. This

!on!lusion was latter !onir$ed b# their ba!terial wilt stud# on to$ato4&G" whi!h illustrated the spe!tral qualit#6s value within a pest !ontrol

progra$ or spa!e1based e!ologi!al lie support s#ste$s. In anotherresear!h" 9!huerger et al. 4*G identiied that blue light dosage in thelight sour!e are !onne!ted to the spe!tral qualit# ee!ts on anato$i!al!hanges in ste$ and lea tissues o peppers.

The !o$pa!t si(e o LEDs allows the$ to be integrated in $edi!altreat$ent devi!e. ,re$an et al. 40G patented a phototherap# gar$entsuitable or treat$ent o newborn Baundi!e. The gar$ent !ontains a

densel# pa!ed blue LED arra# that e$its unior$ high intensit# light.The LEDs are sura!e1$ounted to a!e the liner. An inant who needs

phototherap# !an be wrapped inside the gar$ent to re!eive thetreat$ent on a large area o the sin.

iolet;ultraviolet (210-+%0 n/)

9ignii!ant develop$ent o ultraviolet %+,' LEDs started in late&>>3s when near1+, %+,A" 08410>4 n$' LEDs were popular orinspe!ting anti1!ountereiting water$ars in do!u$ents and !ur1ren!ies. In earl# *3&3s" LEDs in +,C range %*&31*83 n$' also startedto evolve in laboratories using $aterials su!h as alu$inu$ nitride

%*&3 n$' 45G" boron nitride %*&4 n$' 48"4:G" and dia$ond %*04 n$'4>G"Ad$inistering +, light %0*31043 n$'" as reported" helped to

redu!e the si(e o seba!eous glands and the a$ount o sebu$" dirt orlipids that $a# plug olli!le openings 53G. A re!ord o su!!essul a!netreat$ent !ondu!ted under !o$bined illu$ination o violet= blue %;&4n$' and red %500 n$' LEDs **G suggested that repla!ing the laser1

based light sour!e in the devi!e with LEDs should post no signii!antdown ee!t or si$ilar treat$ents.

7ower et al. 5& G investigated the $i!robial +, dose responseso *44=*84 n$ LEDs and *4; n$ low1pressure $er!ur# la$ps toestablish the +, luen!e response o non1pathogeni! $i!roorganis$s.The results o the stud# suggested that +, LEDs are suitable or

point1o1use" low low disine!tion appli!ations although the lowpower output $aes long e/posure ne!essar# to indu!e signii!ant

results. Ater !o$paring a 054 n$ +,A1LED as a sterili(ation devi!eat its highest output with a *4; n$ low1 pressure $er!ur# la$p and a;34 n$ LED" ori et al. 5*G ound that the 054 n$ LED s#ste$ wasable to ina!tivate a variet# o ba!teria depending on the +,A dosagea!!u$ulation. The# suggested that with LED6s saet# and !o$pa!tsi(e" a new t#pe o water sterili(ation devi!e !an be developed.

A ba!teria ina!tivation stud# using +,1A %0&41;33 n$' and +,1C %&331*:3 n$' LEDs indi!ated that the !o$bined wavelengths o*:3=054 n$ and *:3=;34 n$ are best or disine!tion. No ba!terialrea!tivation has been dete!ted in the targeted wastewater ater 53 oe/posure 50G. A stud# that $onitored the enduran!e o e!al

bioindi!ators and the o/idation o organi! $atter and aro$ati!pollutant in wastewaters led to the inding that the !o$bination o +,1

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A and +,1C results in better $i!robial redu!tion ei!ien!# than asingle bandwidth. The ei!ien!# is !o$parable to what a!hievablewith the use o photo!atal#st lie Ti3*5;G"

*( Discussion

Condu!ting a resear!h under a sole wavelength helps to identi#the target appli!ation6s $ost responsive spe!tru$. 9o$eti$es"however" to distinguish the inluen!es o adBa!ent spe!tru$ seg$ents%su!h as inrared and ar red' to !ertain appli!ations are dii!ult

be!ause the spe!tru$ is !ontinuous with no apparent $argins betweenthe neighboring !olors. In general" photo treat$ents are !ondu!ted inthe red to IR seg$ent. Thereore" dierentiating the !onditions thatneeds the treat$ent o red onl# or IR onl# is not stri!tl# ne!essar#.

The studies reviewed in this paper and other related resear!hes54G have shown that LEDs are steadil# repla!ing low1level laser inthe area o LLLT to be!o$e the new avorite or treat$ent or

phototherap# o $edi!al !onditions lie is!he$i! inBur# 55G and

arthritis 58G. LEDs oer an ee!tive alternative to lasers or theollowing reasons?

1( LEDs oer +," NIR" and the entire visible band" while $an# othese spe!tru$ seg$ents are not #et available in se$i!ondu!torlaser.

)( LED arra# is $u!h $ore e!ono$i!al than intense pulsed light%IG" disease !ontrol :3G o plants. Red LEDs areso$eti$es used in ish reprodu!tion stud# :& G as well. Red lightwith supple$ental blue or FR has been the pri$ar# light $i/ oragri!ulture resear!hes even beore the high1brightness1 LED era.

LED6s narrow spe!tral output that overlaps the photos#ntheti!spe!tru$ and its !hara!teristi! that allows the eli$ination o non1un!tioning wavelengths have $ade LED the new avorite or indooragri!ulture.

range! yellow! and green%4331533 n$' are less used in s!ientii!stud# !o$pared to other !olors in the visible spe!tru$. -hen used"the# are oten or !ontrol instead o being the prin!ipal light sour!esthat ai$s toward !ertain results. 9o$eti$es" however" the# do haveopportunities to be!o$e the !enter o the spotlight 9u!h instan!esin!lude" but not li$ited to" bio$ass produ!tion or !arotenoid andatt# a!id $eth#l esters #ields and !he$i!al dete!tions in portableinstru$ents. Note that illu$ination re$ains as the $ost e/pensivea!tor o bio$ass %su!h as algae and $i!roalgae' produ!tion in a!losed photobiorea!tor even though the !ost1 ee!tive te!hnologiesthat produ!e renewable energ# ro$ bio$ass !ontinue to e$erge. In

su!h !ost point o view" green LEDs is hopeul to be!o$e $oresignii!ant in produ!ing !arotenoid pig$ent1ri!h bio$ass in dense!ultures as well as in ish produ!tion :*G and reprodu!tion stud#sin!e green lightHs penetration depth is *3 ti$es over that o pri$ar#

produ!tion !olor.8luelight is possibl# the $ost versatile light sour!e. In addition to

aid the studies o photo!ata#st a!tivation as well as the investigationo ish produ!tion" reprodu!tion" and behavior :0G) blue LEDs have

been used in al$ost all ields o appli!ations reviewed in this paper.As or $> ?E#s! the# are usuall# applied in bio$edi!al resear!hesand environ$ental appli!ations" su!h as dete!tion :;G" disine!tion:4G and photo!ata#st a!tivation :5G.

This review has de$onstrated LEDsH qualii!ation or repla!ingtheir $ore energ# de$anding !ounterparts in a great variet# oresear!h ields. 9in!e *3&3" the patents or LED $anua!turing have

started to e/pire. LED1based appli!ations have a superior outloo inthe !o$ing #ears as the !osts o LEDs be!o$e lower.

c.no%ledgments

This wor is sponsored b# ROC National 9!ien!e Coun!il under

Contra!t N9C&3*1***&1E1;4&133:.