High Power White LED Technology
for Solid State Lighting
Paul S. Martin
J. Bhat,
Bhat, C.C.-H. Chen, D. Collins, W. Goetz, R. Khare,
Khare, A. Kim, M. Krames,
Krames, C.
Lowery, M. Ludowise,
Ludowise, G. Mueller, R. MuellerMueller-Mach, S. Rudaz,
Rudaz, D. Steigerwald,
S. Stockman, S. Subramanya,
Subramanya, SS-C Tan, J. Thompson, T. Trottier
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Copyright (c) Lumileds Lighting LLC Company Confidential
High Power White LEDs
Who is Lumileds
• Fully integrated light source supplier that co-develops optimized system solutions!
• LED dice
• Luxeon Power Light Sources
• Arrays of High Flux LEDs on
a metal core PCB
• Automotive, Traffic Signals, Signage & Contour Solutions
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High Power White LEDs
Outline
• Competition in the market for Illumination, Incandescent & Fluorescent Bulbs.
• LED Metrics
• Options for making white light from LEDs
• Lumileds power white LED performance
• Some interesting demos
3
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Illumination Markets
How Much Energy is Used for Lighting
• In 1999 the US used 3 Trillion kWhr of Electricity!
• 20% or 600 Billion kWhr of Electicity generated was used in Lighting!
• Incandescent/Hal. lamps burn 40% of electricity to produce 15% of light!
• Fluorescent/HID lamps use 60% to produce 85% of light!
• Illumination market is $60Billion/yr and growing slowly, ~2%/yr
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Illumination Markets
Incandescent Bulbs
•
Incandescent = hot light, emitted from a (tungsten) filament at around 2800oK
• Disadvantages:
•
•
•
•
mostly infrainfra-red
glass vacuum envelope & filament both break easily
<15 lm/W luminous (<5% power) efficiency
fire hazard, burnt fingers, maintenance
• Advantages:
Basic disadvantage:
no chance to come close
to DAYLIGHT = 6500oK
black body spectra
2
power spectra, norm.@600 nm
• Radiant cooling
• Cheap 0.0005$/lumen
• klm per package!
1.8
3000K
1.6
1.4
4000
1.2
5500
1
0.8
6500
0.6
0.4
7500
0.2
0
0.3
0.4
Courtesy Gerd Mueller LL
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0.5
0.6
0.7
µm
0.8
0.9
Illumination Markets
Fluorescent Bulbs
• Fluorescent = cold light, emitted by phosphors excited by gas discharge.
• Advantages:
• High efficiency 80+lm/W & High Flux klm/lamp
klm/lamp
• Moderate cost for large lamps 0.002$/lm
• Disadvantages:
• Lifetime short <10,000 hrs resulting in high maintenance.
• Glass vacuum envelope leaks/breaks, ballast noisy.
• Mercury!!
0.025
1.2
1.0
0.02
fluorescent, CCT=3600 K
0.01
Ra = 83
0.4
0.005
Courtesy Gerd Mueller LL
6
0
400
0.6
0.2
450
500
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550
600
650
700
750
nm
0.0
800
rad. flux, a.u.
Basic Advantage:
any color temperature
possible by tri-color mixing
rad. flux, a.u.
0.8
black body 3600 K
0.015
Illumination Markets
Assumptions for using LEDs in lighting
• LED lamps will be far more expensive than incandescent, halogen or
fluorescent lamps for at least a decade.
• The expensive LED lamp must pay for itself through lifetime energy and
maintenance savings.
• The lighting industry has spoiled the users with superb color rendering and
color control.
• Near term LEDs must dominate monochrome and penetrate white niches!
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High Power White LEDs
Outline
• Competition in the market for Illumination, Incandescent & Fluorescent Bulbs.
• LED Technology & metrics
• Options for making white light from LEDs
• Lumileds power white LED performance
• Some interesting demos
8
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LED Metrics
Tower of Babble?
optical power out / electric power in = Wall-Plug-Efficiency, WPE, (%,W/W)
photons out / electrons in = External Quantum Efficiency, EQE, %
photons internally generated / electrons in = Internal Quantum Efficiency , IQE, %
photons out / photons generated = extraction efficiency, %, ηext
photon energy / applied voltage (times electron charge) = electrical efficiency, %, ηel
lumens out / electric power in = luminous efficiency [lm/W]
luminous efficacy, LE [lm/W] = luminous equivalent of the emission spectrum
luminous efficiency = IQE*ηext*ηel*LE
IQE*ηext = EQE
EQE*ηel = WPE
WPE*LE = lm/W
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LED Metrics
LED Skulduggery
Paul’s Top 5 Sins
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What am I hiding?
1) Quoting EQE without Vf or WPE
1) Vf, power efficiency
2) Quoting low duty factor results
2) Thermal resistance, heating
3) Quoting WPE without current or
current density & total power out.
3) GaN in particular has strong
dependence of WPE on current
not much light comes out of a
device at very low currents!
4) Quoting WPE without temperature
4) WPE is strongly dependent on
junction temperature for
AlInGaP, less so for AlInGaN.
5) Quoting Cd without Flux
5) Radiation pattern
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LED Metrics
Tower of Babble take 2 for white LEDs
How well can a source reproduce “natural” colors = Color-Rendering-Index, Ra, %
(100 = sunlight, 85 = office, 60 = cabinet/lantern light)
Color Correlated Temperature = CCT, Kelvin
(x,y coordinates normal to black body curve)
0.9
Phosphor Converted LED = PCLED
LED photons pump phosphor which emits secondary,
and longer, wavelength of light.
CIE1931
Planckian locus
0.8
tungsten, 2850K
0.7
halogen, 3100K
daylight, 6500K
0.6
Stoke’s shift = Difference in wavelength between
absorbed and emitted photons. Emitted photons
always have longer wavelength, i.e. lower
energy!
0.5
0.4
10,000K
2500K
3300K
5000K
0.3
0.2
0.1
0.0
0.0
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0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
High Power White LEDs
Outline
• Competition in the market for Illumination, Incandescent & Fluorescent Bulbs.
• LED Technology & metrics
• Options for making white light from LEDs
• Lumileds power white LED performance
• Some interesting demos
12
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White Light from LEDs
Three methods of Generating LED White Light
• Each method has potential strengths!
Red + Green + Blue LEDs
UV LED + RGB Phosphor
UV LED
Spectrum
Combined
Spectrum
Red Peak
Blue Peak
Phosphor
Emission
Green Peak
410
470
525 590 630
13
470
525
590 630
(nm)
(nm)
RGB LEDs
Binary Complimentary
UV LED + RGB phosphor
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Combined
Spectrum
Phosphor
Emission
Blue LED
Spectrum
470
525 590 630
(nm)
Blue LED
+
Yellow phosphor
White Light from LEDs
Combining Red, Green and Blue LEDs
• Advantages:
• Long term likely the most efficient!
• Dynamic tuning of color temperature possible!
• Excellent color rendering!
• Very large color Gamut available!
• Challenges
• Color Feedback required today to account for LED degradation with T & t!
• Color mixing tricky!
• Yellow-Green Gap!
LED
CCFL
NTSC
EBU
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Combining Red, Green and Blue LEDs
Lumileds LCD Backlight!
• 20 Green, 10 Red, 10 Blue Luxeon’s, ~ 1000 lumens!
• Today LED Solution has 140% Color Gamut and 120% CCFL power!
Both displays showing
the same slide
(red only background)
via a splitter
LED solution
CCFL solution
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White from RGB LEDs
The Yellow-Green Gap!
• Eye Sensitivity Peaks right in the middle of the Yellow-Green GaP!
60
VCSEL
Tj = 25ºC
LEDs
C o n v e r s i o n
50
40
30
Best Laboratory
Result
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Production
Average
10
0
450
470
490
510
530
550
570
590
Wavelength (nm)
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610
630
650
850
White Light from LEDs
UV LED pumped RGB Phosphors
• Advantages:
• White point determined by phosphors ONLY! (i.e. tolerant to LED variation)
• Excellent color rendering possible!
• Theoretically “Simple to manufacture!” (Looks like TV or Fluorescent lamp except
for pump is now UV LED rather than electrons.)
• Temperature stability of phosphors. (Can be great!)
• Disadvantages
• Potential for damaging UV light leakage.
• Fundamental limits on efficiency due to phosphor conversion efficiency, Stokes
shift, self absorption,…
• Challenges
• None available yet!?
• Efficient Blue LED pumped phosphor not available yet?!
• Color uniformity with angle!
• Packaging must be robust to UV exposure.
• Temperature stability of phosphors. (Great phosphors not available in all colors!)
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UV LED pumped RGB Phosphors
UV LED must be >2x Green LED WPE for same lm/W!
• Downshift in color causes fundamental energy loss.
Power Conversion (%)
• Scattering in phosphor + absorption in package (inc. phosphor) reduces extraction
efficiency! Today’s best package efficiency is ~50% for Blue + Yellow phosphor,
UV + RGB phosphor likely to be even worse!
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
370
Assuming 50% pkg. Efficiency!
380
390
400
410
UV Pump Wavelength (nm)
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Red 630nm
Blue 460nm
Green 540nm
White
White + Pkg
420
430
White Light from LEDs
White from Blue LED + Phosphor(s)
• Advantages:
• Simple and single Yellow phosphor versions available today!
• Decent color rendering (Ra = 75 for Blue LED + Yellow Phosphor)
• Temperature stability of phosphors. (Can be great!)
• Disadvantages
• Limits on efficiency due to phosphor conversion efficiency, Stokes shift, self
absorption,…
• Better color rendering (i.e. multi phosphor comes at cost of efficiency)
• Challenges
• Temperature stability of phosphors. (Great phosphors not available in all colors)
• Color uniformity vs. angle
• Multi phosphor versions to improve color rendering
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White from Blue LED + Phosphor(s)
Today, PC LEDs are in the 20-30lm/W range!
• Todays white LEDs are in the ~20-30lm/W range!
0.9
Ce3+ doped garnet family,
e.g.(Y,Gd)3Al5O12
LED, T = 25C
LED,T = 105C
0.8
YAG:Ce
Planckian locus
0.7
530
Combined with the same LED, Ce3+
phosphors hit the Planckian at different
color temperatures:
CIE1931
520
540
0.6
510
0.5
500
70
590
0.4
50
620
630
2500K
0.3
40
3300K
490
30
640
5000K
20
10
0.2
0
400
480
0.1
500
600
700
nm
800
470
460
450 nm
0.0
0.0
20
CCT=4000K, Ra=75
60
600
10,000K
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Ra = 75 is not great (good FL has 83)
but it is OK for some applications.
Copyright (c) Lumileds Lighting LLC Company
White from Blue LED + Phosphor(s)
Color Uniformity can be good for PC White!
CCT (K)
• CCT uniformity of 50-100K is sufficient for high quality illumination.
5400
5200
5000
4800
4600
4400
4200
4000
3800
3600
3400
3200
3000
800K
80K
-85 -75 -65 -55 -45 -35 -25 -15
-5
5
15
Theta (degrees)
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25
35
45
55
65
75
85
White from Blue LED + Phosphor(s)
Progress on Temperature stability of Phosphors
(Y,Gd)AG:Ce
(Y,Gd)AG, 4 mol% Ce
100
[Gd]
0%
I(T)/I(25C), %
80
60
25
40
50
75
20
radiance under 460 nm excitation
measured on powders
25 C
1200000
50
1000000
100
120
800000
150
200
600000
400000
200000
0
400
450
500
550
600
650
700
750
800
nm
0
25
50
75
100
125
150
1200000
25
Temperature, C
1000000
50
100
800000
120
novel phosphors with improved
color specs emerge; in this case
using a Ce3+ - Pr3+ transfer of
excitation energy and yielding
more temperature stable behavior
22
150
600000
200
400000
200000
0
400
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500
600
700
800
White from Blue LED + Phosphor(s)
The 2-phosphor-converted LED – 2pcLED
0.9
1 LED + 2 phosphors
combospec
2.00
Adding green and red to the
blue of the LED opens a huge
color gamut and allows for
de-luxe white of any color
temperature – our best choice
• SrGa2S4:Eu2+ - green
• SrS:Eu2+ - red
Ra = 92
1.50
0.8
1.00
0.50
0.00
400
0.7
530
520
500
600
510
8206
7193
7118
0.5
590
500
0.4
600
10,000K
610
620
630
SrS:Eu
2500K
0.3
The dipole-allowed 5d-4f
transitions of Ce3+ and Eu2+
are uniquely suited for color
converters:
high absorption, small
Stoke’s shift
3300K
490
640
5000K
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
400
0.2
480
0.1
800
HP LED, T = 25C
HP LED,T = 105C
Planckian locus
Phosphors
CIE1931
Series15
540
0.6
700
TG:Eu
470
460
combospec
Ra = 92
500
600
700
800
0.0
0.0
23
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Copyright (c) Lumileds Lighting LLC Company
White Light from LEDs
All three white LED technologies share Three
challenges!
1 Maximize efficiency in lm/W
90 lm/bulb
6 lm/W
0.005 $/lm
2 Maximize flux density in lm/package
3 And of coarse reduce cost $/lm
475 lm/bulb
10 lm/W
0.01 $/lm
24
145 lm/bulb
50 lm/W
0.02 $/lm
Copyright (c) Lumileds Lighting LLC Company
High Power White LEDs
Outline
• Competition in the market for Illumination, Incandescent & Fluorescent Bulbs.
• LED Technology & metrics
• Options for making white light from LEDs
• Lumileds power white LED performance
• Some interesting demos
25
Copyright (c) Lumileds Lighting LLC Company
High Power White LEDs
Gold Wire Bond
Epoxy Dome Lens
LED Chip
p pad
Reflector Cup
semitransparent
contact
Cathode Lead
Anode Lead
n pad
Junction area ~ 0.06mm2
Limitations of conventional 5mm Indicator LED lamps
• Very high thermal resistance, >200°C/W,
• Epoxy limited to <<120°C due to thermal yellowing,
• Light utilization efficiency is low.
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High Power White LEDs
Luxeon™ approach
Die design
•
Large area die for high power capability,
•
Electrode design for low spreading resistance,
•
FlipFlip-chip configuration;
• high extraction efficiency,
• low thermal resistance,
• ability to integrate electronics.
Package design
•
Low thermal resistance package,
•
Stable, soft gel inner encapsulant,
encapsulant,
•
Controlled radiation pattern and efficient optics.
System design
27
•
Low thermal resistance board design,
•
Efficient secondary optical elements.
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High Power White LEDs
Lumileds LuxeonTM Power LED Efficiency
• Leading the charge into Solid State Illumination
Production Typical R&D Demonstrations
350mA If
lm/W
lm/LED
lm/W
lm/LED
Red
44
43
50
50
Red-Orange
55
54
65
65
Amber
36
36
44
44
Green
25
30
50
55
Blue
11
14
15
20
White
18
22
30
36
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LED Technology
Haitz’s Law for LED Flux
• LED Flux per package has doubled every 18-24 months for 30+ Years!!
• 1965 Moore’s Law “# of Transistors/chip will double every 18-24 months!”
Flux/Package (lumens)
1000
100
Luxeon
10
1
Indicator LEDs
0.1
0.01
0.001
1960
1970
1980
1990
Year
29
TM
Copyright (c) Lumileds Lighting LLC Company
2000
2010
High Power White LEDs
Lumileds LuxeonTM Series A & B LEDs
• First ever White LED > 100lm!! (100.2lm and 15lm/W to boot!!)
1000
Luxeon Series B White LED
Flux output (lm)
100
Luxeon Series A White LED
10
Indicator White LED
1
0.1
All data AC 1%DF & 25C case
0.01
0.1
30
1
10
100
Power input (mW)
Copyright (c) Lumileds Lighting LLC Company
1000
10000
High Power White LEDs
Lumileds 100 lumen Club!
• These are the only LEDs that approach “Illumination” flux!
Red
Amber
Green
White
White
31
1000
700
700
1870
1400
105
110
108
100.2
>110
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February-01
December-99
March-01
July-01
1-Sep
High Power White LEDs
What about Radiometric Power?!
• State of the art 400nm indicator LEDs provide 15mW of power.
• How much power can a Luxeon part generate? :-)
Deep Blue 430nm
If (mA) W/LED
Date
1400
>1.0 July-01
Dan
Steigerwald
Talk 4445-19 08:30 8/1/2001
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High Power White LEDs
Lumileds LuxeonTM Series B Cyan LED
• Single Series B Cyan LED can replace an 80W bulb in an 8” traffic ball!
130 lm/bulb
30 lm/W
0.20? $/lm
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High Power White LEDs
Lumileds LuxeonTM Ring
• Fixture design by Philips Lighting and Lumileds.
• 12 Luxeon’s, ~240 lumens. Ring available Now!
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High Power White LEDs
Outline
• Competition in the market for Illumination, Incandescent & Fluorescent Bulbs.
• LED Technology and metrics
• Comparison of options for making white LEDs
• Lumileds power white LED performance
• Some interesting demos
35
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High Power White LEDs
Evolution of LED Package Technology
• Power LEDs can handle ~50x power of an Indicator LED!
Pmax~0.2-0.4W
50 K/W
1994
Pmax~0.1W
150-200 K/W
1970
1962
First Packaged LED
LumiLeds SnapLEDTM
First Power LED
Standard 5mm Lamp
Indicator LED
Indicator LED
36
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Pmax~0.6-4.0W
9-14 K/W
1998
LumiLeds LuxeonTM
Today’s Power LED
High Power White LEDs
Lumileds LuxeonTM Power LED
• Packages designed to handle 1-5W!
High-Power Package:
Improved thermal properties
Heat sink body with good thermal interface
Soft gel inner encapsulant
Including power AlInGaN or AlInGaP or
Phosphor Converted AlInGaN Chip:
qjc~ 12°C/W
High optical efficiency > 95%
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High Power White LEDs
Potential Power Savings vs. Traditional Lighting
• Todays white LEDs are in the ~20-30lm/W range, but still low flux!
100
Incandescent
Power Saved (%)
80
Halogen
60
CFL
40
Fluorescent
20
0
0
25
50
75
100
125
150 175
LED Efficiency (lm/W)
38
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200 225
250
LED Technology
Indicator LEDs vs. Power LEDs
• Indicator LEDs have output powers < ~50mW and Thermal resistances > 50K/W
10
0
InGaN LEDs
λ ~450 nm
-1
10
Output Power (W)
Operating Point
Power LED
-2
10
Operating Point
-3
10
"5 mm" LED
-4
10
10
-3
10
-2
10
-1
0
10
Input Power (W)
39
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10
1
High Power White LEDs
Indicator LEDs vs. Power LuxeonTM LEDs!
• Luxeon’s are designed for low thermal resistance & high current density!
16
120
InGaN LEDs
λd ~530 nm
100
Power LED
Luminous Flux (lm)
Wall Plug Efficiency (%)
20
12
8
4
0
"5 mm" LED
0
50
λd ~530 nm
80
60
Power LED
40
"5 mm" LED
20
0
100
150
200
2
Current Density (A/cm )
40
InGaN LEDs
0
50
100
150
200
2
Current Density (A/cm )
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