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Basics of Backlights
VS
12th June 2007
Holger Dziadek
1
VS
CCFL (Cold Cathode Fluorescence Lamp)
ƒ Edge-Light
ƒ Direct Backlight
LED (Lighting Emiting Diode)
ƒ Edge-Light
ƒ Direct Backlight
ƒ White or RGB
EL (Electro Luminance)
ƒ Direct Backlight
12th June 2007
Holger Dziadek
2
Objectives of the Course
VS
ƒ White LED Technology
– Types of white LEDs
ƒ Design Advantages of the Technology
– Life
– Efficiency
ƒ Design Considerations
– Color matching
– Heat dissipation
– Cost
ƒ Range of Products Available Today
12th June 2007
Holger Dziadek
3
White Through History
VS
Progress in lighting
12th June 2007
Holger Dziadek
4
Progression of White Lighting
12th June 2007
Holger Dziadek
VS
5
Specifying LEDs (in general)
VS
ƒ Type (3mm, 5mm, High Flux, etc.)
ƒ R-G-B with different LED’s
ƒ White LED’s
12th June 2007
Holger Dziadek
6
VS
Definitions—Flux
Radiometric Flux to Luminous Flux
Photopic Eye Response
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
400
450
500
550
600
650
700
Wavelength (nm)
12th June 2007
Holger Dziadek
7
VS
Definitions - Color
White LED
Range
12th June 2007
Holger Dziadek
8
VS
Definition – White
Correlated Color Temperature (CCT)
12th June 2007
Holger Dziadek
9
Definitions – Forward Voltage
VS
ƒ Forward Voltage Vf is roughly equal to the
bandgap energy of the LED semiconductor
divided by the elementary charge
Vf = Eg / q
where q =1.6 x 10-19 coulombs
ƒ Output Intensity of typical high brightness
LEDs is dependent on the Forward Current If
12th June 2007
Holger Dziadek
10
VS
Construction Difference
(5mm versus High Flux LEDs)
Typical construction
for a 5mm LED
Typical
construction for a
High Flux LED
Typical Flux = 3 lm
Typical Flux > 30 lm
Number of LEDs to equal the
output of a 60W incandescent
light bulb = 200
12th June 2007
Number of LEDs to equal the
output of a 60W incandescent
light bulb < 20
Holger Dziadek
11
VS
AlInGaP
Red, Red-Orange
Yellow
AlInGaN
Green, Blue,
White
Group XIII
Group XIV
Group XV
5
6
7
B
C
N
Boron
10.811
Carbon
12.0107
Nitrogen
14.006
13
14
15
Al
Si
P
Aluminum
126.981
Silicon
28.0955
Phosphorus
30.973
31
32
33
Ga
Ge
As
Gallium
69.723
Germanium
72.61
Arsenic
74.921
49
50
51
In
Sn
Sb
Indium
114.818
Tin
118.710
Antimony
121.760
Substrates
Silicon Carbide (SiC)
Sapphire (Al2O3)
Base Elements
P-Type Dopants
N-Type Dopants
12th June 2007
Holger Dziadek
12
How do you make LEDs?
VS
Lens Materials
3 mm and 5 mm
ƒ Epoxy lens
Bad expansion coefficient (stresses bond wire)
– Yellows
– Degradation blue/UV
–
HIGH FLUX
ƒ COC, other hard plastic lens with silicone gel
– Plastic with silicone gel
– Not reflow solderable
ƒ Silicone polymer lens with silicone gel
– Robust for reflow, lead free temperature 260C
– Better moisture handling
– Susceptible to dirt and scratches
ƒ Glass lens with silicone gel
– More robust
– Higher cost
12th June 2007
Holger Dziadek
13
How do you make LEDs?
VS
Substrate Materials
ƒ Sapphire (Al2O3)
– Lower cost (estimated at $3/cm2)
– More transparent (more light output)
– Low thermal conductivity (40 W/m/K)
ƒ Silicon Carbide (SiC)
– Higher cost (estimated at $12/cm2)
– Better ESD protection
– High thermal conductivity (350-490 W/m/K)
12th June 2007
Holger Dziadek
14
How do you make a White LED?
VS
RGB Method
Mixing light from red, green and blue
LEDs (either discrete or combined in one
package) can produce white light
12th June 2007
Holger Dziadek
15
VS
How do you make a
White LED?
Visible LED Pump + Phosphor Method
Blue LED + YAG Cool White
Blue LED + YAG + Other phosphor (red, green, etc.) Warm White
UV LED Pump + Phosphor Method
UV LED + Red phosphor + Green phosphor + Blue phosphor
Luxeon K2
12th June 2007
Holger Dziadek
16
How do you make a White LED?
VS
(Blue + Phosphor) VS (Red + Green + Blue)
Warm White (3500K)
Blue + Phosphor
100 lumens
34 lumens/watt
2.92 watts
Blue
2.3
13.4
0.17
Green
66.7
38.9
1.71
Red
30.7
29.9
1.03
Total
100 lumens
n/a lumens/watt
2.91 watts
8E+12
7E+12
50
6E+12
Radiometric Power (a.u.)
Radiometric Power (a.u.)
60
40
5E+12
4E+12
30
3E+12
20
2E+12
10
0
400
1E+12
0
450
500
550
600
650
700
Wavelength (nm)
12th June 2007
Holger Dziadek
17
VS
How do you make a White LED?
Phosphor Deposition Examples
Lumileds
Lumileds
Seoul Semiconductor
Osram
Cree
12th June 2007
Nichia
Holger Dziadek
18
How do you make a White LED?
VS
Which method is better for making white?
Disadvantages
Advantages
RGB
• Color can be changed
dynamically
• As a luminance source,
millions of colors can be
produced
• Highest theoretical luminous
efficiency of all three methods
• No UV output
• Color can shift due to aging
and temperature
• Requires more sophisticated
electronics
• Poor color rendition
• Fixture efficiency drop caused
by color mixing
12th June 2007
Blue + Phosphor
UV + Phosphor
• High theoretical luminous
• Good color uniformity
efficiency
• Simple driver electronics
• Can provide color
• Potential for limited tint
temperatures between 3200 K variation
(warm white) and 10,000 K
• Eliminates the pump color
(cool white)
variation; only phosphor
• No UV output
variation
• Potential to create variations
in tint
• Must be controlled using
optics and binning
Holger Dziadek
• Lowest luminous efficiency
• Shorter life
• Clouding of the epoxy (UV
packaging problems)
• New phosphors necessary
19
How long do light sources last?
VS
Time to change the lightbulb!
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
ƒ
The sun
Candle
Oil Lamp
Incandescent (Bulb)
Fluorescent (CCFL)
Mercury Vapor
Sodium Vapor
Metal Halide
5mm LEDs
High Flux LEDs
12th June 2007
>4.5 billion years (so far)
<12 hours
<24 hours
1k-1.5k hours
25k-60k hours What is End of Life
for some
10k-20k hours
illumination
24k hours
sources?
20k-30k hours
<10k hours
>20k hours
Holger Dziadek
20
How long do light sources last?
VS
LED Lifetime
How long do they last?
12th June 2007
Holger Dziadek
21
How long do light sources last?
VS
What do we mean by Lifetime?
Traditionally Lifetime was the time it took for 50% of the population of
incandescent bulbs to fail
Many light sources don’t fail catastrophically—Define EOL by reduction in light
output from initial values for example 70% or 50% of initial value
Under what conditions do we measure lifetime?
High Flux LED
5mm LED
Incandescent
12th June 2007
Holger Dziadek
22
VS
How long to light sources last?
Lab60Data on 5mm LED Lifetimes
30 mA, LED PCB temp of 100 C
50
20 mA, LED PCB temp of 80 C
10 mA, LED PCB temp of 40 C
Intensity (candelas)
40
30
20
10
0
0
5000
10000
15000
20000
25000
30000
35000
Time (Hours)
12th June 2007
Holger Dziadek
23
Lifetime (half-life) shortens
with increasing Temperature
and Drive Current
VS
Data extracted from
page 11 of LW Z3SG
data sheet.
Examples OSRAM
12th June 2007
Holger Dziadek
24
Generic white LED lifetime
vs. Temperature
VS
Temperature Solderpoint
Power TOPLED® (LW_E6SG) @ fixed If = 30 mA
3
103*
(*: Ta = 85°C)
2
65
45
1
0
20
40
60
80
100
Lifetime [k h]
12th June 2007
Holger Dziadek
25
Thermal Management Issues
12th June 2007
Holger Dziadek
VS
26
Thermal Management Issues
VS
Which heat sink do I need?
40 °C/W
12th June 2007
or
Holger Dziadek
0.4 ° C/W
27
Manufacturers Examined
VS
ƒ Cree
– XLamp Series
ƒ LumiLeds
– Luxeon Series
– K2 Series
ƒ Nichia
– Jupiter Series
ƒ Osram
– Golden Dragon Series
ƒ Seoul Semiconductor
– Z-Power Series
12th June 2007
Holger Dziadek
28
VS
Temperature
LED
Light Guide
Lost Distance
Cable
PCB
Cooling Fin
CCFL
Light Guide
Hot
Connector
12th June 2007
+25 C
+40 C
Reflector
Holger Dziadek
29
VS
Thermal Management Issues
Calculating Safe Junction Temperatures
LED
LED
LED
Thermal Epoxy
Thermal Epoxy
Thermal Epoxy
Metal Core PC Board
Heat Sink
TJunction = TA + ( PLED ) ⋅ ( RΘ LED ) + ( PLEDs ) ⋅ ( RΘ Heat sin k )
12th June 2007
Holger Dziadek
30
VS
Thermal Management Issues
Increasing from 1W to 3W LEDs
Operating temperature of +25°C
15 °C/W
15 °C/W
15 °C/W
6 °C/W
6 °C/W
6 °C/W
0.1 °C/W
10 ° C/W
TJunction = 25°C + (1W ) ⋅ (21°C / W ) + (3W ) ⋅ (10.1°C / W )
TJunction = 76.3°C
TJunction = 25°C + (3W ) ⋅ (19°C / W ) + (9W ) ⋅ (10.1°C / W )
TJunction = 172.9°C!!!
12th June 2007
Holger Dziadek
31
VS
Thermal Management Issues
Increasing from 1W to 3W LEDs
Operating temperature of +60°C
15 °C/W
15 °C/W
15 °C/W
6 °C/W
6 °C/W
6 °C/W
0.1 °C/W
10 ° C/W
TJunction = 60°C + (1W ) ⋅ (21°C / W ) + (3W ) ⋅ (10.1°C / W )
TJunction = 111,3°C
TJunction = 60°C + (3W ) ⋅ (19°C / W ) + (9W ) ⋅ (10.1°C / W )
TJunction = 207,9°C!!!
12th June 2007
Holger Dziadek
32
Datasheet Lumens
vs Actual Lumens
VS
1-Watt LEDs, 25 °C ambient temperature
Datasheet: 45 Lumens at a 25 °C die temperature
Dynamic resistance: 1 Ω
Temperature coefficient of Vf: -2.0 mV/ °C
15 °C/W thermal resistance for the LED
6 °C/W thermal resistance for the thermal epoxy and PCB dielectric
10 °C/W for the heatsink, board interface, etc.
Relative Luminous Flux
120
100
80
60
40
20
0
0
20
40
60
80
100
120
Die Junction Temperature (°C)
12th June 2007
Holger Dziadek
33
Cool White LED Comparison
Osram LW W5SG Cool
Osram ZW W5SG Cool
Osram LW W5SN Cool
Osram LW W5SM Cool
Osram LEW E3A Cool
Osram LEW E3B Cool
Osram LEW E2A Cool
Osram LEW E2B Cool
Lumileds LXHL-PW01 Cool
Lumileds LXHL-DW01 Cool
Lumileds LXHL-BW02 Cool
Lumileds LXHL-PW09 Cool
Lumileds LXHL-DW09 Cool
Lumileds LXHL-PW03 Cool
Lumileds LXK2-PW etc Cool
Nichia NCCW002, etc Cool
Nichia NS6W083 Cool
Cree XL7090 Cool
Cree 3XL7090 Cool
Cree XL7090XR Cool
Seoul Semi W10190 Cool
Seoul Semi W10290 Cool
Seoul Semi W10490 Cool
Cotco LD-700AWN1-70 Cool
12th June 2007
Thermal
Viewing
Typical Typical Typical RestistTypical Lumens
Dice
Angle
350 500 700 1000 1400 1500 Current Voltage Power
ance
°C/W
mA
Vf
W
#
Degees
mA mA mA mA mA mA
1
120
21-39 41
350
3.8
1.3
9
1
120
33-71 60
350
3.2
1.1
15
1
120
52-97
700
3.8
2.7
8
1
120
64
350
3.2
1.1
15
6
120
300
700
22.5
15.8
3.6
6
120
420
700
22.5
15.8
3.6
4
120
200
700
15
10.5
5
4
120
280
700
15
10.5
5
1
120
45
350
3.42
1.2
15
1 Side-emit 40.5
350
3.42
1.2
15
1
Batwing
45
350
3.42
1.2
15
1
120
65
80
700
3.7
2.6
13
1 Side-emit
58
70
700
3.7
2.6
13
4
150
87.4
700
6.84
4.8
8
1
150
52.5
87.5 110
135
1000
3.72
3.7
9
1 35,70,120
42
?
350
3.7
1.3
17
4
120
60
?
350
3.6
1.3
10
1
100
52
?
350
3.5
1.2
17
1
100
76
700
4
2.8
17
1
100
53.5
?
350
3.5
1.2
8
1
70,110
52
350
3.5
1.2
8
2
70,110
103
700
3.5
2.5
6
4
70,110
178
1400
3.5
4.9
4
1
70
27
350
3.6
1.3
15
Holger Dziadek
VS
Rise
LED
Max
Only Junction
°C
°C
12
125
17
125
21
135
17
125
57
150
57
125
53
150
53
125
18
135
18
135
18
135
34
135
34
135
38
135
33
150
22
105
13
120
21
125
48
145
10
145
10
125
15
125
20
125
19
125
CRI
80
80
80
80
80
80
80
80
70
70
70
70
70
70
70
80
80
75
75
75
70
70
70
34
White is White is White
VS
Binning Issues
Osram White Binning
12th June 2007
Holger Dziadek
35
White is White is White
VS
Binning Issues
Seoul White Binning
12th June 2007
Holger Dziadek
36
VS
Chromaticity
Binning Comparison
0.5
Osram Cool
Osram Warm
Lumileds Cool
0.45
Lumileds Warm
Nichia Cool
0.4
Nichia Warm
y
Cree XL
Cree XR
0.35
2500 Kelvin
15000 Kelvin
Seoul Cool
Seoul Warm
0.3
Cotco Cool
Blackbody
0.25
0.2
0.2
12th June 2007
0.25
0.3
0.35
0.4
x
Holger Dziadek
0.45
0.5
0.55
0.6
37
VS
Spectral and Chromaticity
Measurements
0.5
2.00E-03
0.45
1.80E-03
0.4
Y
0.35
1.60E-03
Luminous Flux (a.u.)
0.3
1.40E-03
0.25
0.2
1.20E-03
0.2
0.3
0.4
X
0.5
0.6
CreeXL7090WHT
1.8E+13
CreeXL7090WW
SeoulW32180
SeoulN32180 1.6E+13
LumiledsPW12 K2
LumiledsLXHL-BL03
1.4E+13
NichiaNCCW022
NichiaNCCL023
1.2E+13
OsramLW W5SG
3500k Blackbody
1E+13
1.00E-03
8E+12
8.00E-04
6E+12
6.00E-04
4E+12
4.00E-04
2E+12
2.00E-04
0.00E+00
400
12th June 2007
0
450
500
550
600
Wavelength (nm)
Holger Dziadek
650
700
750
38
VS
CCT Change with Time
12000
Conditions:
350 mA
25C Ambient
Correlated Color Temp (CCT K)
11000
10000
Supplier 1
Supplier 1
Supplier 1
Supplier 2
Supplier 3
Supplier 4
Supplier 5
Supplier 6
Supplier 6
9000
8000
7000
6000
5000
4000
3000
2000
0
12th June 2007
500
1000
1500
Time (hours)
Holger Dziadek
2000
39
VS
CCT Change with Time
12000
Conditions:
500 mA
25C Ambient
Correlated Color Temp (CCT K)
11000
10000
Supplier 1
Supplier 1
Supplier 1
Supplier 2
Supplier 3
Supplier 4
Supplier 4
Supplier 4
Supplier 5
Supplier 6
9000
8000
7000
6000
5000
4000
3000
2000
0
12th June 2007
500
1000
Time (hours)
Holger Dziadek
1500
2000
40
VS
CCT Change with Time
12000
Conditions:
350 mA
75C Ambient
Correlated Color Temp (CCT K)
11000
10000
Supplier 1
Supplier 1
Supplier 1
Supplier 2
Supplier 3
Supplier 4
Supplier 5
Supplier 6
Supplier 6
9000
8000
7000
6000
5000
4000
3000
2000
0
12th June 2007
500
1000
Time (hours)
Holger Dziadek
1500
2000
41
CCT Change with Time
VS
0.0006
480 hours
960 hours
1176 hours
1464 hours
1632 hours
1824 hours
Luminous Flux (a.u.)
0.0005
0.0004
0.0003
0.0002
0.0001
0
400
12th June 2007
450
500
550
600
Wavelength (nm)
Holger Dziadek
650
700
750
42
VS
Luminous Flux Change
with Time
120%
Conditions:
350 mA
25C Ambient
Relative Luminous Flux (%)
100%
Supplier 1
Supplier 1
Supplier 1
Supplier 2
Supplier 3
Supplier 4
Supplier 5
Supplier 6
Supplier 6
80%
60%
40%
20%
0%
0
12th June 2007
500
1000
Time (hours)
Holger Dziadek
1500
2000
43
VS
Luminous Flux Change with
Time
120%
Conditions:
500 mA
25C Ambient
Relative Luminous Flux (%)
100%
Supplier 1
Supplier 1
Supplier 1
Supplier 2
Supplier 3
Supplier 4
Supplier 4
Supplier 4
Supplier 5
Supplier 6
80%
60%
Outliers are likely from
measurement error
40%
20%
0%
0
12th June 2007
500
1000
Time (hours)
Holger Dziadek
1500
2000
44
VS
Luminous Flux Change with
Time
120%
Conditions:
350 mA
75C Ambient
Relative Luminous Flux (%)
100%
Supplier 1
Supplier 1
Supplier 1
Supplier 2
Supplier 3
Supplier 4
Supplier 5
Supplier 6
Supplier 6
80%
60%
40%
20%
0%
0
12th June 2007
500
1000
1500
Time (hours)
Holger Dziadek
2000
45
The Cost of Light
Lamp Type
Incandescent
Flourescent
High Pressure Mercury
High Pressure Sodium
Metal Halide
W hite LED (Luxeon K2)
W atts
Life
60
32
250
250
400
5
1.000
24.000
24.000
24.000
20.000
50.000
Cost of Light =
Where
12th June 2007
VS
Initial
Lumens
850
3.000
11.000
28.000
36.000
100
Maintained
Lumens
850
2.900
8.500
27.000
24.000
75
[ p + h ] / L + [W x R]
F
Price
$0,90
$1,50
$21,00
$27,00
$70,00
$3,50
Luminous
Efficiency
14
91
34
108
60
15
klm/$
$/Mlmh
0,94
2,00
0,52
1,04
0,51
0,03
$12,82
$1,18
$3,06
$0,97
$1,82
$8,67
(in $ / Mlm-hr)
p is the lamp price (in cents)
h is the labor cost to replace lamp (in cents) assumed to be 400¢
L is the lamp life (in hours)
F is the lamp flux output (in lumens)
W is the lamp input power (in watts)
R is the energy cost (in cents/kW-hr) assumed to be 10¢
Holger Dziadek
46
Luminous Efficiency
Improvement Trends
12th June 2007
Holger Dziadek
VS
47
VS
CCFL – Light Intensity
Light Guide
Light
Hot
Reflector
Connector
Relative Intensity (%)
100
80
60
40
20
0
0
20
40
60
80
100
Length of CCFL (mm)
12th June 2007
Holger Dziadek
48
LED – On The Side
VS
overexposed Area
12th June 2007
Holger Dziadek
49
VS
LED – Light Intensity
Light Guide
Lost Distance
Cable
PCB
Cooling Fin
underexposed Area
12th June 2007
overexposed Area
Holger Dziadek
50
VS
LED – Backside
LCD
DBEF-Film
BEF-Film
Bulk Diffuser
PMMA Plate
Cable
PCB
Cooling Fin
overexposed Area
underexposed Area
12th June 2007
Holger Dziadek
51
VS
White LED Trends
60
50
20
40
15
30
10
20
5
0
2002
12th June 2007
10
2003
2004
2005
Year
Holger Dziadek
2006
Luminous Efficiency (lumens/watt)
White Light Cost (Cents/Lumen)
25
0
2007
52
VS
Advantage vs Disadvantage
Issue
CCFL
LED
++
--
Homogeneous of Luminance
+
-
Dimmable
-
++
Lifetime@-30°C
--
++
[email protected]°C
+
++
Lifetime@+25°C
++
+
Lifetime@+60°C
++
--
Lifetime@+85°C
++
---
Environmental
--
+
Color Stabilization
++
+
+
+
++
-
-
+
--
+
Useable for Ex-Protected Area
-
++
Medicine Application
+
++
++
-
Size
Brightness Stabilization
Lost Temperature
EMI
Driving Voltage
Price of System
12th June 2007
Holger Dziadek
Note
very good for automotive
very bad for automotive
CCFL mercury is very low
For the same brightness
approx. +20%
53
LED-Converter vs Resistor
VS
Examples for three HBLEDs with resistor
R-limit
= (Vin - (3 * Vfwd)) / Ifwd
= (12V - (3 * 3.0V)) / 0.5A
= 6 ohms
P-limit
= Ifwd2 * R-limit
= 0.52 * 6
= 1.5 Watts
P LEDs
= 3 * Vfwd * Ifwd
= 3 * 3.0V * 0.5A
= 4.5 Watts
Efficiency = PLEDs / (PLEDs + Plimit
= 4.5W/ (4.5W + 1.5W)
= 75% Not too impressive!
Ifwd
= (Vin - (3 * Vfwd)) / Rseries
= (11.4V - (3 * 3.0V) / 6 ohms
= 0.4 Amps
Delta Vin = +/-5% variation of the +12V power supply will yield a +/- 20% variation in LED current — and therefore
in LED brightness and life time. Of course, this variation could be reduced by increasing the voltage across the
dropping resistor, but this would make the electrical efficiency only worse.
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LED-Converter vs Resistor
VS
Examples for three HBLEDs with Converter
R-limit
= (Vin - (3 * Vfwd)) / Ifwd
= (12V - (3 * 3.0V)) / 0.5A
= 6 ohms
P-limit
= Ifwd2 * R-limit
= 0.52 * 6
= 1.5 Watts
P LEDs
= 3 * Vfwd * Ifwd
= 3 * 3.0V * 0.5A
= 4.5 Watts
Efficiency = Converter
= >89% impressive!
Ifwd
= (Vin - (3 * Vfwd)) / Rseries
= (11.4V - (3 * 3.0V) / 6 ohms
= 0.4 Amps
Delta Vin = +/-5% variation of the +12V power supply will yield a +/- 0% variation in LED current !!
12th June 2007
Holger Dziadek
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VS
LED-Converter
Power Systems Converter
Data sheet PS-LD0609-01
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Holger Dziadek
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VS
LED-Converter
Power Systems Converter
Data sheet PS-LD0101-01
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Holger Dziadek
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Advantage vs Disadvantage
VS
LED and CCFL will life in harmony together.
Both technologies have advantages and disadvantages.
Our all customer need to decide what they need and want.
Our job is to explain them the technologies.
Good success.
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Holger Dziadek
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