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11 Copyright (c) Lumileds Lighting LLC Company ConfidentialCopyright (c) Lumileds Lighting LLC Company Confidential
LED CharacteristicsLED CharacteristicsErik Swennen & Patrick van der MeulenErik Swennen & Patrick van der Meulen
22Copyright (c) Lumileds Lighting LLC Copyright (c) Lumileds Lighting LLC
Lumileds ConfidentialLumileds Confidential
LED Characteristics
•• Basic Optical UnitsBasic Optical Units•• Human visionHuman vision
•• Eye SensitivityEye Sensitivity•• Color VisionColor Vision
•• ColorimetryColorimetry•• Color space xyColor space xy•• Dom. Wavelength CCTDom. Wavelength CCT
•• Working Principle of an LEDWorking Principle of an LED•• Optical and Electrical CharacteristicsOptical and Electrical Characteristics•• LED BinningLED Binning
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33Copyright (c) Lumileds Lighting LLC Copyright (c) Lumileds Lighting LLC
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LED Characteristics
•• Basic Optical UnitsBasic Optical Units•• Human visionHuman vision
•• Eye SensitivityEye Sensitivity•• Color VisionColor Vision
•• ColorimetryColorimetry•• Color space xyColor space xy•• Dom. Wavelength CCTDom. Wavelength CCT
•• Working Principle of an LEDWorking Principle of an LED•• Optical and Electrical CharacteristicsOptical and Electrical Characteristics•• LED BinningLED Binning
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Φ
Flux (units: lumen, watts)
The The amountamount of of light radiatedlight radiatedbyby a a light sourcelight source..
Unit: Unit: lumenlumen (lm (lm -- photometricphotometric))Watts (W Watts (W -- radiometricradiometric))
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Luminous Flux Measurement
Baffle
• LumiLeds test method• Test method measures total luminous flux emitted into a defined
acceptance angle
Device under test Defined acceptance angle
Photometrically weightedoptical detector
Φv ≈ Electrical signalarea spherearea detectorSphere with highly
reflective whitediffuse coating oninside surface
θ
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�
Intensity (unit: candela (lm/sr), W/sr)
The The amountamount of of light radiatedlight radiatedbyby a a light sourcelight source in a in a given directiongiven direction..
1 1 candelacandela = 1 = 1 lumenlumen per per steradiansteradian
�
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Luminous Intensity Measurement
Device under test
• Test method only accounts for luminous flux in a small portion of optical beam
Iv ≈ Electrical signal d2
Area detector
ω≈ Area detectord2d
Photometrically weightedoptical detector
ω
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LED Characteristics
•• Basic Optical UnitsBasic Optical Units•• Human visionHuman vision
•• Eye SensitivityEye Sensitivity•• Color VisionColor Vision
•• ColorimetryColorimetry•• Color space xyColor space xy•• Dom. Wavelength CCTDom. Wavelength CCT
•• Working Principle of an LEDWorking Principle of an LED•• Optical and Electrical CharacteristicsOptical and Electrical Characteristics•• LED BinningLED Binning
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Radiometry & Photometry
•• Radiometric light is specified according to its Radiometric light is specified according to its radiant energy and power without regard for the radiant energy and power without regard for the visual effects of radiation. Prefix: visual effects of radiation. Prefix: RadiantRadiant or or RadiometricRadiometric
•• Photometric light is specified as radiation in Photometric light is specified as radiation in terms of human visible response according to the terms of human visible response according to the CIE standard observer response curve (photopic CIE standard observer response curve (photopic luminous efficiency function). Prefix: luminous efficiency function). Prefix: LuminousLuminous
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wavelength (nm) →
rela
tive
eye
sens
itivi
ty →
4000
500 600 700 800
V(λ)
555 nm0,2
0,4
0,6
0,8
1,0
1 W555nm = 683 lm
Eye Sensitivity
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From Watts to Lumens
WavelengthWavelength LuminousLuminous ConversionConversionEfficiencyEfficiency Factor [lm/W]Factor [lm/W]
400 400 0.004 0.004 0.30.3450 450 0.040.04 2626500 500 0.3 0.3 221221555 555 1.0 1.0 683683600 600 0.63 0.63 431431650 650 0.11 0.11 7373700 700 0.0040.004 2.82.8
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Basics of human vision•• Light projected on the retina by Light projected on the retina by
the lensthe lens•• Retina contains light sensitive Retina contains light sensitive
cells cells –– rods & conesrods & cones•• Rods are more sensitive, no Rods are more sensitive, no
color difference (scotopic vision)color difference (scotopic vision)•• Cones have color sensitive Cones have color sensitive
pigments pigments –– red, green & blue red, green & blue (photopic vision)(photopic vision)
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LED Characteristics
•• Basic Optical UnitsBasic Optical Units•• Human visionHuman vision
•• Eye SensitivityEye Sensitivity•• Color VisionColor Vision
•• ColorimetryColorimetry•• Color space xyColor space xy•• Dom. Wavelength CCTDom. Wavelength CCT
•• Working Principle of an LEDWorking Principle of an LED•• Optical and Electrical CharacteristicsOptical and Electrical Characteristics•• LED BinningLED Binning
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Colorimetry•• Basic quantity for colorimetry is the spectrum S(Basic quantity for colorimetry is the spectrum S(λλ))•• ‘standard observer’ CIE 1931 :color matching functions‘standard observer’ CIE 1931 :color matching functions
X, Y and Z are called the tristimulus valuesX, Y and Z are called the tristimulus values•• Y represents brightness (nit, lumen, ... )Y represents brightness (nit, lumen, ... )•• Many different spectra can yield the sameMany different spectra can yield the same
color for the human eye (metamerism) color for the human eye (metamerism) ⇒there is no way back from XYZ to spectrumthere is no way back from XYZ to spectrum
300 400 500 600 700 8000
0.5
1
1.5
2x-ba ry-ba rz -ba r
λd).λ(x).λ(S.683X780
380∫=
λd).λ(y).λ(S.683Y780
380∫=
λd).λ(z).λ(S.683Z780
380∫=
400 500 600 700 8000
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
wa ve le ngth (nm )
colo
r mat
chin
g va
lue
CIE x-ba rCIE y-ba rCIE z -ba r
300 400 500 600 700 8000
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
wavelength (nm)
colo
r mat
chin
g va
lue
CIE x-barCIE y-barCIE z-bar
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Colorimetry
xyxy--diagram CIE1931diagram CIE1931
ZYXXx++
=ZYX
Yy++
=3y12x2
x4'u++−
=3y12x2
y9'v++−
=
u’v’u’v’--diagram CIE1976diagram CIE1976
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Peak or Dominant Wavelength
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
x coordinates
480
460
500
520
540
560
580
600
620640
Dominant Wavelength
CIE Illuminant E
(x, y) Coordinate
ab
baPurityColor =
0.00.10.20.30.40.50.60.70.80.91.0
400 450 500 550 600 650 700Wavelength (nm)
Rel
ativ
e In
tens
ity
RED
AMBERROYAL BLUE
BLUE
CYAN
GREEN
Color purity = a / b
Dominant wavelength (Illuminant E)
Peakwavelength = highest radiometric energy
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Visual perception of white light
The color impression of light is characterized by:
• Color temperature (Tc)• Color rendition (Ri) • Reflection properties of material being illuminated
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Blackbody radiators
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Color Coordinates of Blackbody (Planckian) Radiators
x coordinates
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
y co
ordi
nate
s
480
460
500
520
540
560
600
620640Blue Dwarf
Star20K-50K
CIE Illuminant E
NTSC White6500K
Cool-whiteFluorescent5400K
12V Halogen Bulb 3000K
Household Incandescent 2800K
12V Instrument Cluster Bulb 2500K
Warm-whiteFluorescent 3000K
M.P. Iron1810K
M.P. Tungsten3700K
M.P. Copper 1360K
"Red-hot" Poker (1000K = 1340F)
580
Tc = 5500K
Tc = 2200K
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Color Temperature in CIE1931 Diagram
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
x coordinates
480
460
500
520
540
560
580
600
620640
50,000K20,000K
10,000K
8000K 6667K5714K
5000K
∞
4444K 4000K
3636K
3333K3077K
2857K2500K
1667K2000K
Planckian Locus
CIE Illuminant E
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Color Rendering Index
Sunlight Has a CRI of 100. When objects are illuminated with sunlight, all the colors look good.
Low Pressure Sodium has a CRI less than 0. Objects illuminated by it all look brown.
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Color Rendering CalculationLight Grayish Red Light Bluish Green
Dark Grayish Yellow Light Blue
Strong Yellow Green Light Violet
Moderate Yellowish Green
Light Reddish Purple
400 500 600700
400 500 600700400 500 600700
400 500 600700
400 500 600700 400 500 600700
400 500 600700 400 500 600700
Wavelength [nm]
• Spectra of 8 definedsamples are combined withthe spectrum of the source(e.g. White LED)
•The shift of the color point of every sample is calculated:
R1 to R8
•The average Ra shift is then calculated:
•Ra = 1/8 (R1 + R2 +...+ R8)
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Color Rendering Index (Ra)
•• RRaa = 90 = 90 -- 100100Excellent Excellent colorcolor rendering propertiesrendering properties
•• RRaa = 80 = 80 -- 9090Good Good colorcolor rendering propertiesrendering properties
•• RRaa = 60 = 60 -- 8080Moderate Moderate colorcolor rendering propertiesrendering properties
•• RRaa < 60< 60Poor Poor colorcolor rendering propertiesrendering properties
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LED Characteristics
•• Basic Optical UnitsBasic Optical Units•• Human visionHuman vision
•• Eye SensitivityEye Sensitivity•• Color VisionColor Vision
•• ColorimetryColorimetry•• Color space xyColor space xy•• Dom. Wavelength CCTDom. Wavelength CCT
•• Working Principle of an LEDWorking Principle of an LED•• Optical and Electrical CharacteristicsOptical and Electrical Characteristics•• LED BinningLED Binning
13
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Working Principle of an LED
•Same principle for all colors
(AlInGaP & InGaN)
•Power dissipation:1-5 Watt
•Package Extraction Efficiency: >95%
•Maximum Ratings
•Tjunction-max = 120 °C / 135°C
• Iforward-max = Product dependent
Iforward
(Electrons)
Vforward
φvisible (Photons)
PN-Junction
Electrical Model
Anode
Cathode
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InGaN vs AlInGaP LED Technology
Anode
Cathode
Blue3.4 V at 350 mA
7 V at -100 uA
Anode
Cathode
Red/Amber3.0 V at 350 mA
20V at -100 mA
InGaN AlInGaP
GaP Substrate( ~ 200 µm)
AuZn Contact Pad
n-Al0.5In0.5P (LCL)
(AlxGa1-x)0.5In0.5PActive Layer
VPE GaP Window( ~ 50 µm)
p-Al0.5In0.5P (UCL)
LED JunctionSilver reflector
InGaNSapphire
Light
Wire bond Silicon submount
LED Junction
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Luxeon Slug Electrical PotentialLuxeon Slug Electrical Potential
SlugAlInGaP Die in 1WBatwing Package
SlugInGaN Die in all
Luxeon Packages
LED Chip
Cathode LeadAnode Lead
BodyPlastic Lens
Slug
slug
SlugAlInGaP Die in 1W Lambertian & SideEmitter Package
+
-+
-
-
+
+
-
+ OR -
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LED Characteristics
•• Basic Optical UnitsBasic Optical Units•• Human visionHuman vision
•• Eye SensitivityEye Sensitivity•• Color VisionColor Vision
•• ColorimetryColorimetry•• Color space xyColor space xy•• Dom. Wavelength CCTDom. Wavelength CCT
•• Working Principle of an LEDWorking Principle of an LED•• Optical and Electrical CharacteristicsOptical and Electrical Characteristics•• LED BinningLED Binning
15
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Light Output Characteristics•• Flux with CurrentFlux with Current•• TTjunctionjunction = 25= 25ooCC
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Light Output vs Junction Temp
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Forward Current Characteristics
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Wavelength Characteristics
0.00.10.20.30.40.50.60.70.80.91.0
400 450 500 550 600 650 700Wavelength (nm)
Rela
tive
Inte
nsity
RED
AMBERROYAL BLUE
BLUE
CYAN
GREEN
Dominant Wavelength:
RED=629nm GREEN=530nm
AMBER=590nm CYAN=505nm
BLUE=470nm
ROYAL BLUE=455nm
Spectral Halfwidth:
RED=19nm GREEN=35nm
AMBER=19nm CYAN=30nm
BLUE=25nm
ROYAL BLUE=20nm
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LED Characteristics
•• Basic Optical UnitsBasic Optical Units•• Human visionHuman vision
•• Eye SensitivityEye Sensitivity•• Color VisionColor Vision
•• ColorimetryColorimetry•• Color space xyColor space xy•• Dom. Wavelength CCTDom. Wavelength CCT
•• Working Principle of an LEDWorking Principle of an LED•• Optical and Electrical CharacteristicsOptical and Electrical Characteristics•• LED BinningLED Binning
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Luxeon Binning Example: Green
Batch to Batch
Variations
Num
ber o
f Par
ts P
rodu
ced
M
13.9
N
18.1
O
23.5 30.6
1.31.3
Flux bins
Bin Limits [lm]
Ratio Upper/Lower 1.3
L P
Num
ber o
f Par
ts P
rodu
ced
G
2.79
H
3.03
J
3.27 3.51
0.240.24
Voltage bins
Bin Limits [V]
Bin Width [V] 0.24
Batch to Batch
Variations
F K
Num
ber o
f Par
ts P
rodu
ced
2
525
3
530
4
535 540
5.05.0
Color bins
Bin Limits[nm]
Bin Width [nm] 5.0
Batch to Batch
Variations
1 5 6
Bining
=
Subdividing large quantities
into manageable quantities
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Luxeon Binning
•• Lumileds LEDs are 100% electrically and optically testedLumileds LEDs are 100% electrically and optically tested
•• Each unit is binned for Each unit is binned for •• Luminous Flux, Luminous Flux, •• Forward Voltage Forward Voltage •• Dominant Wavelength or Correlated Color TemperatureDominant Wavelength or Correlated Color Temperature
• All binning is done at • nominal current• Junction Temperature of 25°C (Flash mode)
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LED Parameter vs.Temperature
0
1
2
570 580 590 600 610 620 630
Wavelength [nm]
Rel
ativ
e In
tens
ity
+25°C
+85°C
λpeak
Tamb = -20°C
As temperature rises:
• Light Output decreases
• Wavelength gets longer (towards red), except for White
• Forward Voltage decreases
0
50
100
150
200
250
300
350
400
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0Forward Voltage (V)
Forw
ard
Cur
rent
(mA
)
Red, Reddish Orange,
Amber(AlInGaP)
Royal Blue, Blue, Cyan,
Green, White (InGaN)
∆Vf ≈ -2mV / °C
Amber
19
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Dominant λ vs. Temperature
As LED’s get hotter, colors shift to longer wavelengths.NOTE: This number is different for λpeak
Example: What is the color shift of an amber LED whose Tj is 40°C? What will λD be at Tj 40 °C?
λD1 = 590 nm (@T1= 25 °C)λD2 = ? nm (@T2= 40 °C)
∆ λD (λD2-λD1) ∆ T (T2-T1)
∆ λD = (.09 nm/ °C)* (T2-T1) = (.09 nm/ °C)*(40 -25 °C) = 1.35 nm
Therefore, λD2 = 591.35 nm
)( Cnm/TλD °∆∆
≈ K
Color K (nm/ºC)Amber .09
Red .03
Blue .04
Green .04
Cyan .04
=
= .09 nm/ °C
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LED CharacteristicsLED CharacteristicsErik Swennen & Patrick van der MeulenErik Swennen & Patrick van der Meulen