LED ACADEMY by OMS Lighting, Ltd.

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1. LED BASICS1.1. How LED worksA light-emitting diode (LED) is a semiconductor device that emits light on certain wavelength (color). A die (active areaof LED) is encased in plastic or ceramic housing. The housing may incorporate one or many dies. When LED is forwardbiased(switched on), electrons are able to recombine with holes within the device, releasing energy in the form ofphotons (Figure 1.1.1). This effect is called electroluminescence.Figure 1.1.1:Reflective cupWhen LED is switched on, electronsrecombine with holes within thedevice, releasing energy in the formof photons with certain wavelength(color).Photon: Unit of lightEmitted lightMoldedepoxy lensAnoded wirePositiveterminalNegativeterminalp-type GaNActive regionn-type GaNPhotonAnode leadHoleCathode leadElectronThe term SSL (Solid State Lighting) is common term for LED technology being used for lighting applications. It refers totechnology in which the light is emitted by solid-state electroluminescence as opposed to incandescent bulbs (where thelight is emitted via thermal radiation in visible part of spectrum – incandescence).White LED working principleThe most common method involves coating LEDs of one color (mostly blue LEDs made of InGaN) with phosphor (Figure1.1.2a) of different colors to form white light; the resultant LEDs are called phosphor-based white LEDs. The “blue”photons emitted by High-brightness LED (HB LED) (Figure 1.1.2b) either passes through the phosphor layer withoutalteration, or they are converted to the “yellow” photons in the phosphor layer (Figure 1.1.2c). The combination of“blue” and “yellow” photons leads to white light (Figure 1.1.2d). In order to watch explanatory animation please visithttp://www.omslighting.sk/ledacademy/276/introduction.Figure 1.1.2:a) Cross-section of standardphosphor-based white HB LED.b) Recombination of electrons withholes results to “blue” photons.c) “Blue” photons either passesthrough the phosphor layerwithout alteration, or they areconverted to the “yellow” photonsin the phosphor layer.d) Combined together, they createwhite light.positiveterminalnegativeterminalphosphorlayern-type semiconductoractive region or junctionp-type semiconductora) b)“blue” photon passingthrough phosphor layer“yellow” photon excited by“blue” photon in phosphor layer“blue” photonsrecombination of electrons withholes results to “blue” photons“blue” and “yellow”photons createdwhite lightphospor layerc) d)Spectrum of a phosphor-based white LED clearly showing blue light directly emitted by the LED die and the morebroadened yellow light emitted by the phosphor (Figure 1.1.3).Figure 1.1.3:White light can be produced onlyby combining blue and yellowlight. Sir Isaac Newton discoveredthis effect when performingcolor-matching experiments inearly 1700s.Intensity (counts)4000350030002500200015001000Blue peakYellow phosphor5000300 350 400 450 500 550 600 650 700 750 800Wavelength (nm)1LED ACADEMY/LED BASICS
Figure 1.2.1:Various light sources versus LED.1.2. LED basic parametersFigure 1.2.1 depicts basic parameters of LED light source compared with the most common traditional light sources. LEDshows better or at least comparable numbers for all important parameters than traditional light sources.Lamp type Incandescent bulb Halogen lamp Metal halide lamp Mercury vapor lamp LEDLED ACADEMYTechnicalIncandescent bulb makeslight by heating metalfilament wire to light temperatureuntil it glows.Halogen gas increases thelifetime of the wolframfilament and avoid the darkeningof the bulb. The bulbcan be operated on highertemperatures, which allowscolder CCT.Adding rear earth metal saltsto mercury vapor lamp enableshigh efficiency. It workson high pressure and temperatures,so special fixturesare required. The advantageis the compact size incomparison to fluorescentand incandescent lamps.Mixture of halides influencesthe CCT. After 10 000 hoursthe lumen output is approx.83% of nominal.The outer bulb is coatedwith a phosphor for thermalinsulation and converts someUV emissions into red light.After 2000 hours only 50%of nominal light output.Compact and highly durablelight source enables bothnew designs and advantagesin the light control. LEDs areswitched on instantly andthis makes applications withfrequent switching easy.Tunable white and RGBversions are already on themarket. LEDs offer severalbenefits which can be employedin combination withall well being applications.Efficacy (lm/W) 6 - 16 16 - 30 75 - 125 40 - 75 80 - 160Input power (W) 20 - 60 55 - 100 20 - 24 000 50 - 500 0,2 - 100Hazardous chemicalcontentno Halogens Argon, Mercury Argon, Mercury no*Electronic ballast no in general no needed to control thecurrentCRI 100 100 70 - 95 40 - 60 65 - 97Application Indoor, outdoor Indoor applications likeshops, residentialFloodlight, outdoor, shopsneededOutdoor applications,streetlights, facadeneededIndoor, outdoorAdditional info high IR radiation high IR radiation High UV radiation High light pollution little UV and IR radiationLifetime (hours) 1000 1000 - 3000 6000 - 20 000 4000 50 000CCT (K) 2700 2700 - 3500 3800 - 7000 3200 - 4200 2700 - 8000Dimmable yes, 0 - 100% yes, 0 - 100% yes, 50 - 100% no yes, 0.1 - 100%Lamp type Compact fluorescent lamp Fluorescent lamp Low pressure sodium High pressure sodium LEDTechnicalLight output decreasesshortly after first use 5-10%,end of lifetime is approx.70-80%. Full power is notreached after 1 second.The latest versions are CCFL(cold cathode). In general,for outdoor applications allFLs have problems at lowerambient temperatures,sometimes it is not possibleto start lamp.The lamp reaches best efficacyif the temperature of lampcold-spot is around 35°C.A problem is stroboscopiceffect in some applications.Problems occur at lowerambient temperatures,sometimes it is not possibleto start the lamp. After25 000 hours lumen outputdecreases down to 50%.LPS lamps have an outerglass vacuum envelopearound the inner dischargetube for thermal insulation.Yellow light is very insectfriendly. The fact is the lightsource is quite spacious andthe recycling process costsa lot of money. Practically,this type of the lamp isrunning out version becauseof low CRI.Smaller than LPS. Yellowlight is insect friendly.Compact and highly durablelight source enables bothnew designs and advantagesin the light control. LEDs areswitched on instantly andthis makes applications withfrequent switching easy.Tunable white and RGBversions are already on themarket. LEDs offer severalbenefits which can be employedin combination withall well being applications.Efficacy (lm/W) 46 - 80 70 - 120 up to 200 100 - 150 80 - 160Input power (W) 10 - 50 8 - 80 10 - 180 50 - 600 0,2 - 100Hazardous chemicalcontentSmall amount of Mercury Mercury, Neon Sodium, Neon, Argon Sodium, Neon, Argon,MercuryElectronic ballast needed or build in needed needed needed neededCRI 80 - 90 80 - 99 30 25 - 85 65 - 97Application Indoor applications Indoor Outdoor, streetlight, security Outdoor, streetlight, security Indoor, outdoorAdditional infoFrequent on/off reducelifetime; high UV radiationFrequent on/off reducelifetime; high UV radiationReaches full brightness rapidly;no lumen degradationover lifetime; relatively biglight sourceLess light pollution as Mercuryvapor lamps; frequenton/off reduce lifetimeno*little UV and IR radiationLifetime (hours) 15 000 15 000 - 45 000 16 000 - 23 000 10 000 - 24 000 50 000CCT (K) 2700 - 5000 2700 - 8000 difficult to describe 2000 - 3000 2700 - 8000Dimmableyes, 3 - 100%, continuous yes, 3 - 100%, continuousdim damage the light source dim damage the light sourceno yes, 50 - 100% yes, 0.1 - 100%*LEDs have to be, as all semiconductor devices, disposed in a correct way, otherwise hazardous chemicals such as arsenic or phosphorus may occur.2
Page 1: C=42.Reflective cupEmitted lightMol
Page 5 and 6: Figure 1.2.4:The black-body curve (
Page 7 and 8: 60º60º60º60º30ºC0 / C1800ºcd
Page 9 and 10: Figure 2.3.3:Examples of the most u
Page 11 and 12: Aluminium - it is the most common m
Page 13 and 14: ConductionWhen a temperature gradie
Page 15 and 16: 3.5. Thermal design of LED-based lu
Page 17 and 18: Figure 3.6.1:a) Passive coolingb) A
Page 19 and 20: Figure 3.7.6:Air gaps between two s
Page 21 and 22: Figure 4.2.1:Relative luminous flux
Page 23 and 24: Figure 4.3.3:LEDs in serial/paralle
Page 25 and 26: 4.5. LED driver additional features
Page 27 and 28: LED ACADEMY27
Page 29 and 30: Figure 5.4.1:Unlike traditional lig
Page 31 and 32: LED ACADEMY31
Page 33 and 34: Figure 6.2.1:LotusLotusAccent light
Page 35 and 36: Figure 6.4.1:Gacrux - microprism li
Page 37 and 38: 6.6. Architecture, facade, city mar
Page 39 and 40: 6.8. House, flat and living areaDes
Page 41 and 42: Figure 7.1.5:Solid state lighting m
Page 43: Figure 7.4.3:OMCVD FAB development

LED ACADEMY by OMS Lighting, Ltd.

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