fundamentals of l-state light - gbv · 2014-10-07 · fundamentals of l-state light leds, oleds,...
TRANSCRIPT
Fundamentals of
l-State Light
LEDs, OLEDs, and Their
Applications in
Illumination and Displays
VINOD KUMAR KHANNA
Cc^ CRC PressTaylor & Francis CroupBoca Raton London NewYork
CRC Press is an imprint of the
Taylor & Francis Group, an Informa business
Contents
Preface xxv
Acknowledgments xxxi
Author xxxiii
Acronyms, Abbreviations, and Initialisms xxxv
PART I History and Basics of Lighting
Chapter 1 Chronological History ofLighting 3
Learning Objectives 3
1.1 How Early Man Looked at the "Sun" 3
1.2 The Need for Artificial Light Sources 3
1.3 First Steps in the Evolution ofArtificial Lighting 4
1.4 The First Solid-State Lighting Device 4
1.5 The First Practical Electrical Lighting Device 4
1.6 The Incandescent Filament Lamp 6
1.7 Mercury and Sodium Vapor Lamps 7
1.8 The Fluorescent Lamp 7
1.9 The Compact Fluorescent Lamp 8
1.10 Revolution in the World of Lighting: Advent of
Light-Emitting Diodes 8
1.11 Birth ofthe First LED and the Initial Stages of LED
Development 8
1.12 The Father ofthe LED: Holonyak Jr. 11
1.13 The Post-1962 Developments 11
1.14 Haitz's Law 11
1.15 AlGaAs LEDs Grown on GaAs Substrates 12
1.16 AlGalnP LEDs on GaAs Substrates 12
1.17 Acquisition of Generated Light 12
1.18 The AlInGaN Material System: Blue and White LEDs 13
1.19 High-Power LEDs 13
1.20 LEDs and Materials Science 14
1.21 The Omnipresent Elements: Ga, N, and As 14
1.22 Further Refinements 15
1.23 Discussion and Conclusions 15
References 16
Review Exercises 17
Chapter 2 Nature and Quality of Lighting 19
Learning Objectives 19
2.1 What Is Light? 19
vii
viii Contents
2.1.1 Dual Nature ofLight 19
2.1.2 Properties of Light Waves 21
2.1.3 Electromagnetic Spectrum 22
2.2 Vision 24
2.3 Opaqueness, Color, and Transparency ofMaterials to Light 25
2.4 Photometry 26
2.5 Colorimetry, Radiometry, and Photometry 28
2.6 Upcoming Colorimetric Metrics for Solid-State Lighting 31
2.6.1 Color Quality Scale 31
2.6.2 Gamut Area Index 32
2.6.3 Statistical Approach 32
2.7 Discussion and Conclusions 32
References 33
Review Exercises 33
Chapter 3 Conventional Light Sources 35
Learning Objectives 35
3.1 Competing Light Sources 35
3.2 Incandescent Filament Bulb 36
3.3 Tungsten Halogen Lamp 37
3.4 High-Pressure Mercury Vapor Lamp 38
3.5 Metal Halide Lamp 40
3.6 Low-Pressure Sodium and High-Pressure Sodium VaporLamps 40
3.7 Fluorescent Tube and Compact Fluorescent Lamp 41
3.8 Performance Comparison of Different Traditional LightSources 44
3.9 Discussion and Conclusions 45
References 46
Review Exercises 46
Chapter 4 LED-Based Solid-State Lighting 49
Learning Objectives 49
4.1 LED Diode Family 49
4.2 LED Construction 50
4.3 Quasi-Monochromatic Nature of Emission 50
4.4 Red LED 51
4.5 White LED 52
4.6 Indicator- and Illuminator-Type LEDs 54
4.7 Preliminary Ideas of SSL 54
4.7.1 The Term "Solid-State Lighting" 55
4.7.2 Meaning of Illumination 55
4.7.3 A Display Device 55
4.8 Why Solid-State Lighting? 56
4.9 Drawbacks of SSL 58
Contents ix
4.10 Potential and Promises of SSL 59
4.10.1 The Monochrome Era: Early 1960s to
Late 1990s 59
4.10.2 The Beginning of LED General Illumination:
2000-2011 60
4.10.2.1 Performance of SSL Luminaire 60
4.10.2.2 LED Street Light 60
4.10.3 2011 Onwards... 60
4.11 Discussion and Conclusions 60
References 61
Review Exercises 62
PART II Inorganic LEDs
Chapter 5 Physical Principles of Inorganic LEDs 65
Learning Objectives 65
5.1 Understanding Lighting Processes from Luminescence
Theory 65
5.2 Injection Luminescence: The Most Efficient
Electroluminescence 67
5.3 Mechanisms of Electron and Hole Recombination in
Semiconductors 69
5.3.1 Radiative Recombination Mechanisms 69
5.3.2 Nonradiative Recombination Mechanisms 79
5.4 Recombination Rates of Excess Carriers and Excess-
Carrier Lifetimes 81
5.4.1 Radiative Recombination Rate (C/rad) and Carrier
Lifetime (rf) 81
5.4.2 Nonradiative Recombination Rate (Rni) and
Carrier Lifetime (rnf) 84
5.4.3 Overall Lifetime of Excess Carriers and Radiative
Efficiency of LED 86
5.5 Discussion and Conclusions 90
References 90
Review Exercises 91
Chapter 6 Homojunction LEDs 93
Learning Objectives 93
6.1 Homojunction in Equilibrium 93
6.2 Reverse-Biased Homojunction 97
6.3 Forward-Biased Homojunction 106
6.4 Injection Efficiency of Homojunction LEDs 109
6.5 Discussion and Conclusions 110
References 111
Review Exercises 111
x Contents
Chapter 7 Heterojunction LEDs 113
Learning Objectives 113
7.1 Increasing Injection Efficiency in LEDs 113
7.2 Isotype and Anisotype Heterojunctions: Notational
Conventions and Band Diagrams 114
7.3 Energy Band Offsets in Semiconductors 115
7.4 Advantages ofHeterojunctions 120
7.5 Current Injection Ratio Estimation 120
7.6 Single Heterojunction LED 123
7.7 Double Heterojunction LED 127
7.8 Quantum Well Heterostructure LED 129
7.8.1 Notion of a Quantum Well,
129
7.8.2 Avoidance of Lattice Mismatch-Induced
Defects by Using Thin Active Layer 133
7.8.3 Electronic Motion in a Quantum Well 133
7.8.4 Operation of a Quantum Well LED 133
7.8.5 Radiative Transitions in a Quantum Well 134
7.8.6 Effect of Electric Field on the Energy Bands
in a Quantum Well 134
7.8.7 Injection Efficiency Improvement by Additional
Layer Incorporation 134
7.8.8 Forward Current-Voltage Characteristics of
Quantum Well LED 135
7.9 Comparison of Homo- and Heterojunction LEDs 136
7.10 Discussion and Conclusions 136
References 137
Review Exercises 138
Chapter 8 Surface- and Edge-Emitting LEDs 141
Learning Objectives 141
8.1 LED Designs Based on Direction of Light Emission 141
8.2 Surface-Emitting LED 142
8.3 Edge-Emitting LED 144
8.4 Superluminescent LED 146
8.5 Discussion and Conclusions 147
References 149
Review Exercises 149
Chapter 9 Light Extraction from LEDs 151
Learning Objectives 151
9.1 Total Internal Reflection of Light and the EscapeCone Concept 152
9.2 Techniques of Improving Light Extraction 154
9.2.1 Increasing the Number of Escape Cones 154
Contents xi
9.2.2 Pyramidal Reflectors 155
9.2.3 Distributed Bragg Reflectors 156
9.2.4 Resonant Cavity LEDs 156
9.2.5 Crown-Shaped Patterned Sapphire Substrates 157
9.2.6 Roughened and Textured Surfaces 157
9.2.7 Surface-Plasmon LED 158
9.2.8 Preventing Absorption Losses 159
9.2.9 Photon Reincarnation and Recycling 159
9.3 Extraction Efficiency Formula for a Single-EscapeCone LED 160
9.3.1 Fractional Solid Angle Factor 160
9.3.2 Semiconductor-Epoxy Transmittance (7^SE) Factor 160
9.3.3 Epoxy-Air Transmittance (TEA) Factor 164
9.3.4 Combination of the Extraction EfficiencyFactors and Assumptions 164
9.3.5 Generalization to an TVEscape Cone-LEDStructure 164
9.3.6 Escape Cone Engineering in Planar,
Rectangular LEDs 165
9.4 Efficiency Enhancement by Making Nonplanar,Nonrectangular LEDs 169
9.5 Discussion and Conclusions 170
References 172
Review Exercises 173
Chapter 10 Semiconductor Materials for Inorganic LEDs 175
Learning Objectives 175
10.1 Material Requirements for LED Fabrication 175
10.2 Common LED Materials 177
10.2.1 AlGaAs Materials 177
10.2.2 AlGalnP Materials 182
10.2.3 AlInGaN Materials 184
10.3 Discussion and Conclusions 187
References 188
Review Exercises 189
Chapter 11 Fabrication ofInorganic LEDs 191
Learning Objectives 191
11.1 Heterostructure Growth Methods: LPE and MOCVD 191
11.1.1 Liquid-Phase Epitaxy 192
11.1.2 Metal Organic Chemical Vapor Deposition 193
11.2 LED Substrates 194
11.3 GaN Diode Processing Steps 196
11.3.1 GaN Growth Using GaN Buffer Layer 196
11.3.2 N-Type Doping of GaN 197
xii Contents
11.3.3 P-Type Doping of GaN 197
11.3.4 Ohmic Contact on N-Type GaN 197
11.3.5 Ohmic Contact on P-Type GaN 198
11.3.6 GaN Etching and Substrate Removal 198
11.4 Representative Process Sequences of GaN LED
Fabrication 198
11.4.1 On Sapphire Substrate 198
11.4.2 On Silicon Substrate 199
11.4.3 On Silicon-on-Insulator Wafer 199
11.5 Discussion and Conclusions 202
References 206
Review Exercises 208
Chapter 12 Packaging of LEDs 209
Learning Objectives 209
12.1 Through-Hole Packaging 210
12.2 SMT-Based Packaging 210
12.2.1 SMT LED Packaging 211
12.2.2 SMT Leadform Packaging 212
12.2.3 SMT Leadless Packaging 215
12.3 COB LED Packaging 215
12.4 Silicon LED Packaging 216
12.5 Heat Produced during LED Operation, and Reliabilityof LED Plastic Packages 217
12.6 Discussion and Conclusions 218
References 219
Review Exercises 219
Chapter 13 LED Performance Parameters 221
Learning Objectives 221
13.1 Characteristic Parameters of LEDs 221
13.1.1 Feeding Efficiency (7]feed) 221
13.1.2 External Quantum Efficiency (T]ext) 222
13.1.3 Radiant Efficiency or Wall-Plug Efficiency (T7e) 222
13.2 Current-Voltage Characteristics of LEDs 223
13.3 Current-Controlled Behavior of LEDs 225
13.4 Forward Voltage Drop (VF) across an LED 225
13.5 Reverse Breakdown Voltage (VR) of an LED 226
13.6 Efficacy ofan LED and the Difference between
Efficacy and Efficiency 228
13.7 Optical Parameters of the LED 229
13.7.1 Optical Spectrum 229
13.7.2 Spectral Line Half-Width or Full Width
at Half-Maximum 231
Contents xiii
13.7.3 CCTandCRI 233
13.7.4 Color Coordinates 233
13.7.5 Light Distributions 233
13.7.6 Included Angle ofan LED 233
13.7.7 Viewing or Beam Angle of an LED 234
13.7.8 Binning 237
13.7.9 Tolerance of Parameters 23713.8 Discussion and Conclusions 237
References 238Review Exercises 238
Chapter 14 Thermal Management of LEDs 241
Learning Objectives 24114.1 Short-Term Effects of Temperature on LED Performance 241
14.1.1 Effect ofTemperature on Electrical Behavior
of LED 241
14.1.2 Effect of Temperature on Optical CharacteristicsofLED 243
14.2 LED Lifetime Concept 24314.3 Long-Term Influence ofTemperature on Different Parts
of the LED 244
14.3.1 White LED Die 244
14.3.2 Phosphor 245
14.3.3 Encapsulant 246
14.3.4 Package 24614.4 Effect ofThermal Cycling on LED Performance 246
14.5 Correlation of LED Lifetime with ThermallyRelated Parameters 247
14.5.1 Temperature Rating and LED Lifetime 24714.5.2 Pulsed Current Flow and LED Lifetime 247
14.5.3 Thermal Analysis of LEDs 247
14.5.4 Electrical and Thermal Analogies 247
14.5.5 Series and Parallel Combinations of
Thermal Resistors 250
14.5.6 Thermal Paths to the Ambient and Mechanisms
of Heat Removal through Air 25414.6 Maximizing Heat Loss from LED 255
14.6.1 Conduction Enhancement 255
14.6.2 Convection Enhancement 256
14.6.3 Radiation Enhancement 25614.6.4 Heat Removal from LED Driving Circuitry 256
14.7 Discussion and Conclusions 256
References 258
Review Exercises 258
xiv Contents
Chapter 15 White Inorganic LEDs 261
Learning Objectives 261
15.1 Primary, Secondary, and Complementary Colors 261
15.2 Wavelength Conversion and Color Mixing Techniques 262
15.3 Wavelength Conversion Examples 264
15.4 Color Mixing Examples 267
15.5 Relative Advantages and Disadvantages ofWhite LightRealization'Methods 269
15.6 Quality ofWhite LED Emission 271
15.6.1 Measurement Standards and Protocols 271
15.6.2 Temperature Dependence 272
15.6.3 Radiation Pattern Variation with
Emission Angle 272
15.6.4 White LED Ageing Effects 272
15.6.5 Measuring Instruments 273
15.7 Discussion and Conclusions 273
References 274
Review Exercises 275
Chapter 16 Phosphor Materials for LEDs 277
Learning Objectives 277
16.1 Nonusability of Traditional Phosphors in LEDs 277
16.2 Desirable Requirements for White LED Phosphors 278
16.3 Opportunities for LED Phosphors 279
16.4 Phosphor Location in LEDs 279
16.5 Phosphor Constitution 281
16.6 Phosphor Preparation 282
16.7 Types of Phosphors 282
16.8 Oxide Phosphors 283
16.9 Oxynitride Phosphors 286
16.10 Nitride Phosphors 287
16.11 Oxyhalides and Halide Phosphors 288
16.12 Sulfide Phosphors 288
16.13 Inorganic-Organic Hybrid Semiconductors as
Phosphors 288
16.14 Organically Capped CdSe Quantum Dots and
Sr3Si05:Ce3+, Li+ Phosphors 289
16.15 Discussion and Conclusions 289
References 291
Review Exercises 292
Chapter 17 High-Brightness LEDs 295
Learning Objectives 295
17.1 Defining High-Brightness LEDs 295
17.2 Necessity of High-Brightness LEDs 296
Contents xv
17.3 Number of Converters Required for Low- and
High-Brightness LEDs 297
17.4 Lateral Structures ofHigh-Brightness LEDs 297
17.5 Vertical Architecture of High-Brightness LEDs 300
17.6 Laser Lift-Off Process for Sapphire Substrate Removal 302
17.7 Heat Removal and Protection against Failure Modes 304
17.8 Colors ofHigh-Brightness LEDs 305
17.9 Photonic Crystal LEDs 305
17.10 Encapsulant Materials for High-Brightness LEDs 307
17.11 Applications ofHigh-Brightness LEDs 307
17.11.1 Pocket Projectors 307
17.11.2 Backlighting 308
17.11.3 Flashlights 308
17.11.4 General Illumination 308
17.11.5 Automotive Headlamps and Signal Lamps 309
17.12 Discussion and Conclusions 309
References 310
Review Exercises 310
PART III Organic LEDs
Chapter 18 Organic Semiconductors and Small-Molecule LEDs 315
Learning Objectives 315
18.1 Organic Materials and Semiconductors 315
18.1.1 Organic Semiconductors: A Subset of OrganicMaterials 315
18.1.2 Saturated and Unsaturated Organic Materials 316
18.1.3 Special Characteristics of Organic Semiconductors 316
18.2 Electroluminescent Materials for OLEDs 319
18.2.1 Fluorescent and Phosphorescent Molecules 319
18.2.2 Singlet and Triplet Excitons 319
18.2.3 Singlet Emitters 319
18.2.4 Triplet Emitters 319
18.2.5 Efficiencies from Triplet and Singlet Molecules 320
18.3 Types of Organic Semiconductors 320
18.3.1 Small Molecules and Polymers 320
18.3.2 Bandgaps of Small Molecules and Polymers 321
18.4 Early Organic Optoelectronic Materials and the First
Organic LED 321
18.4.1 Renewal of Interest in Anthracene 321
18.4.2 Small-Organic-Molecule LED 322
18.4.3 Roles of Constituent Layers 322
18.4.4 Operating Mechanism of Small-Molecule
LED and Multifunctionality of Layers 324
xvi Contents
18.5 Energy Band Diagram of OLED 324
18.6 High-Efficiency OLED 326
18.7 Discussion and Conclusions 326
References 327
Review Exercises 328
Chapter 19 Polymer LEDs 329
Learning Objectives 329
19.1 Moving to Polymers 329
19.2 Polymer LED Operation 330
19.3 Internal Quantum Efficiency ofPolymer LED 331
19.3.1 Matching the Number of Holes and Electrons
Reaching the Polymer Layer 331
19.3.2 Using Several Polymer Layers 331
19.3.3 Polymer Doping 331
19.3.4 External Quantum Efficiency of
Polymer LED 331
19.4 Energy Band Diagrams ofDifferent Polymer LED
Structures 332
19.4.1 ITO/Polymer (MEH-PPV)/Ca LED 332
19.4.2 ITO/Polymer (MEH-PPV)/A1 LED 332
19.4.3 ITO/(MEH-PPV + CN-PPV)/AlLED 332
19.4.4 ITO/(PEDOT:PSS + MEH-PPV)/Ca LED 332
19.5 Fabrication of Polymer LED 337
19.6 Differences between Small-Molecule and Polymer LEDs 337
19.7 Organic LEDs, Inorganic LEDs, and LCDs 338
19.8 Discussion and Conclusions 342
References 342
Review Exercises 343
Chapter 20 White Organic LEDs 345
Learning Objectives 345
20.1 Obtaining White Electroluminescence 345
20.1.1 Necessary Conditions 345
20.1.2 Foundation Approaches 346
20.2 Single Emitter-Based WOLED Schemes 346
20.2.1 Solitary Molecular Emitters Forming Excimers/
Exciplexes or Electromers 346
20.2.1.1 Excimers and Exciplexes 346
20.2.1.2 Electromers 346
20.2.1.3 Red Shift in Excimer and Electromer
Emission Wavelengths 346
20.2.1.4 WOLED Examples Using Excimers 347
20.2.1.5 WOLED Example Using Electromer 348
20.2.1.6 Advantages and Disadvantages 348
Contents xvii
20.2.2 Single Polymers or Molecules EmittingSeveral Colors 348
20.2.2.1 Convenience and Drawbacks of the
Single Polymer Approach 348
20.2.2.2 Examples of WOLEDs 348
20.2.3 Single Color-Emitting OLED with a Down-
Conversion Layer 349
20.2.3.1 Blue+ Orange Mixing 349
20.2.3.2 Using UV Source 350
20.3 Multiple Emitter-Based WOLEDs 350
20.3.1 Single Stack: Multiple Emitters Blended in a
Single Layer 350
20.3.1.1 For-and-Against Qualities 350
20.3.1.2 Mixing Polymers with Two
Complementary or Three
Fundamental Colors 351
20.3.1.3 Doping Small Proportions ofOneor More Molecular Emitters in a
Wide Bandgap Host 351
20.3.2 Stacked Layers Emitting Different Colors 351
20.3.2.1 Optimizing the Roles of Layers 351
20.3.2.2 Vertical Red-Green-Blue Stack 351
20.3.2.3 Horizontal RGB Stack 352
20.4 Discussion and Conclusions 352
References 353
Review Exercises 354
PARTN LED Driving Circuits
Chapter 21 DC Driving Circuits for LEDs 359
Learning Objectives 359
21.1 Features of DC Sources 359
21.2 Cell and Battery 359
21.3 Battery and Capacitor 363
21.4 Linear Transistor Regulator 364
21.5 Switch-Mode Power Supply 365
21.6 Buck Converter 366
21.7 Boost Converter 370
21.8 Buck-Boost Converter 372
21.9 LED Dimming 373
21.10 Lifetime ofthe Driving Circuit 374
21.11 Series and Parallel Strings of LEDs 374
21.11.1 Series Connection 374
21.11.2 Parallel Connection 375
xviii Contents
21.12 Discussion and Conclusions 376
References378
Review Exercises 379
Chapter 22 AC Driving Circuits for LEDs 381
Learning Objectives381
22.1 AC Mains Line 381
22.2 Rectification 382
22.3 Digital Methods of LED Driving 384
22.4 Analog Methods of LED Driving 385
22.5 Power Quality of AC-Driven LED Lighting 386
22.5.1 Power Factor of LED Circuits 386
22.5.2 Total Harmonic Distortion in LED Circuits 388
22.5.3 Resistor-Type and Buck Convertor
LED Circuits 390
22.6 AC LEDs 390
22.7 Applications Requiring DC or AC LEDs 391
22.8 Capacitive Current Control LEDs 392
22.9 Discussion and Conclusions 393
References 394
Review Exercises 395
PARTV Applications of LEDs
Chapter 23 LEDs in General Illumination 399
Learning Objectives 399
23.1 LED-Based Illumination 399
23.1.1 Local or Specialty Lighting 400
23.1.2 General Lighting 400
23.2 Retrofit LED Lamps 401
23.3 LED Bulbs 402
23.3.1 Low-Wattage LED Bulbs 402
23.3.2 Medium-Wattage LED Bulbs 402
23.3.3 High-Wattage LED Bulbs 403
23.3.4 Bases of LED Bulbs 403
23.3.5 Main Parameters of LED Bulbs 403
23.3.6 LED Multicolor Bulbs 403
23.3.7 LED Bulbs in Cars 404
23.3.8 Other Uses ofLED Bulbs 405
23.4 LED Tube Lights 406
23.4.1 Fluorescent Tubes versus LED Tubes 406
23.4.2 Applications and Parameters ofLED Tubes 406
23.4.3 LED Color Tubes 407
23.5 LED Street Lights 407
Contents xix
23.5.1 LED Street Lamps versus Conventional Lamps 407
23.5.2 Ratings of LED Street Lamps 411
23.5.3 LED Light Strip Lights 411
23.6 LED Light Bars 412
23.7 Discussion and Conclusions 413
References 413
Review Exercises 414
Chapter 24 Large-Area OLED Lighting 415
Learning Objectives 415
24.1 Paradigm Shift in Lighting Industry 415
24.1.1 Classical Notion of a Glaring Point Source
of Light 415
24.1.2 New Lighting Concepts 416
24.2 OLED Tiles and Panels 418
24.2.1 Representative Commercial OLEDTile Examples 419
24.2.2 Reversible OLED Building Tiles 419
24.3 Challenges of Large-Area Mass ManufacturingOLED Technology 420
24.3.1 Short Circuit Issue 420
24.3.2 Nonuniform Light Emission 420
24.3.3 Heat Generation 421
24.4 Discussion and Conclusions 422
References 422
Review Exercises 423
Chapter 25 Inorganic LED Displays 425
Learning Objectives 425
25.1 Definitions 425
25.2 Main Components of an LED Display 425
25.3 Types of LED Displays 427
25.3.1 Alphanumeric Displays 427
25.3.2 Color Video Displays 427
25.4 Seven-Segment LED Displays 428
25.4.1 Construction 428
25.4.2 Common Cathode and Common Anode
Configurations 429
25.4.3 Advantages and Limitations 430
25.4.4 Operation 431
25.4.5 Examples ofLED Displays 434
25.5 Resolution of LED Video Image 434
25.5.1 Minimum Viewing Distance and Pixel Pitch 434
25.5.2 Choosing the Correct Pixel Pitch: ImageQuality and LED Screen Cost 435
xx Contents
25.6 Virtual Pixel Method to Enhance Image Quality 436
25.6.1 Necessity ofVirtual Pixel 436
25.6.2 Misleading Resolution Claims 437
25.7 Types of Virtual Pixels 437
25.7.1 Geometrical/Squared Virtual Pixel 437
25.7.2 Side Effects 439
25.7.3 Interpolated Virtual Pixel 440
25.7.4 Advantages over Geometrical Pixel 441
25.8 Building Larger LED Screens by Assembly of
Elementary Modules 441
25.9 Gamma Correction 441
25.10 Examples of LED Screens 442
25.10.1 Single-Color LED Display Module 442
25.10.2 Dual-Color LED Display Module 442
25.10.3 Full-Color LED Display Module 443
25.11 LED Television (LED-Backlit LCD Television) 443
25.11.1 Edge-Lit LED TV 444
25.11.2 Full-Array RGB LED TV 445
25.11.3 Dynamic RGB LED TV 44525.11.4 Pros and Cons of LED TV 446
25.12 Flexible Inorganic LED Displays 447
25.13 Discussion and Conclusions 448
References 449
Review Exercises 450
Chapter 26 Organic LED Displays 451
Learning Objectives 451
26.1 Evolution of Displays 45126.1.1 From Bulky to Lightweight Displays 451
26.1.2 Two Types of OLED Displays 451
26.2 Passive Matrix Organic LED Display 45226.2.1 Construction and Working Principle 452
26.2.2 Advantages 45226.2.3 Drive Arrangements and Difficulties 452
26.2.4 Applications 45326.3 Active Matrix Organic LED Display 453
26.3.1 Benefit ofDriving with Active Matrix 453
26.3.2 Construction and Operation 45326.3.3 Backplane of the Display 455
26.3.4 Advantages 45526.3.5 Problems and Applications 455
26.4 TFT Backplane Technologies 45626.4.1 Conventional and Hydrogenated Amorphous
Silicon (a-Si and a-Si: H) TFT 456
26.4.2 Low-Temperature-Poly-Silicon TFT 457
Contents xxi
26.4.3 Metal-Oxide Thin-Film Transistor 457
26.4.4 Nanowire Transistor Circuitry 458
26.4.5 Choosing among Different BackplaneTechnologies 458
26.5 OLED Mobile Phone, TV, and Computer Displays 458
26.6 Discussion and Conclusions 460
References 461
Review Exercises 461
Chapter 27 Miscellaneous Applications of Solid-State Lighting 463
Learning Objectives 463
27.1 Power Signage 463
27.1.1 Traffic Lights 464
27.1.2 Automotive Signage 465
27.1.3 Other Signage Applications 466
27.2 Fiber Optic Communication Using LEDs 466
27.2.1 Structures and Materials of the LEDs Used 466
27.2.2 LEDs versus Laser Diodes 467
27.3 Wireless Communication with Infrared and Visible
Light Using LEDs 467
27.3.1 Optical Wireless Technology 467
27.3.2 Use of LEDs in Wireless Communication 468
27.4 Medical Applications of LEDs 469
27.4.1 Operation Theater Light 469
27.4.2 HEALS Treatment 469
27.4.3 Skin-Related Therapies 469
27.4.4 Treating Brain Injury 470
27.4.5 Vitamin D Synthesis and Cytometry 471
27.4.6 LED-on-the-Tip Endoscope 471
27.5 LEDs in Horticulture 471
27.6 Discussion and Conclusions 472
References 472
Review Exercises 473
Chapter 28 Smart Lighting 475
Learning Objectives 475
28.1 Infusing Intelligence or Smartness in Lighting Buildings 475
28.1.1 At the Planning Stage of a Building 475
28.1.2 Five Steps after the Building Is Constructed 476
28.1.3 Aims and Scope of Smart Lighting Technology 476
28.1.4 Computer Networking 477
28.1.5 Programming Needs 477
28.1.6 Emergency Lighting 477
28.2 Smart Lighting Control System 477
28.2.1 Daylight Harvesting 478
xxii Contents
28.2.2 Occupancy Control 478
28.2.3 Personal Control 479
28.2.4 Time Scheduling 479
28.2.5 Task Tuning 479
28.2.6 Control by Load Shedding 479
28.2.7 Other Options 480
28.2.8 Dirt Accumulation Prevention and Removal 480
28.3 Occupancy Sensing Devices 480
28.3.1 Types of Occupancy Sensors 480
28.3.2 Occupancy Sensor Features 482
28.4 Daylight-Sensing Devices 482
28.5 Design Aspects 484
28.6 Night-Time Exterior Lighting 484
28.6.1 Preferred Light Sources for Night Illumination 485
28.6.2 Glare Reduction 485
28.6.3 Preventing Light Pollution 485
28.6.4 Light Trespassing on Neighborhood 485
28.6.5 Light Uniformity, Facial Recognition, Shadow
Effects, Surface Reflectances, and Finishes 486
28.6.6 Biological Effects of Colors 486
28.6.7 Exterior Lighting Controls 486
28.7 Discussion and Conclusions 486
References 487
Review Exercises 487
PART VI Future of lighting
Chapter 29 Opportunities and Challenges of Solid-State Lighting 491
Learning Objectives 491
29.1 Prospective Growth in Solid-State Lighting 491
29.1.1 LED General Lighting during the Years
"2012-2020" 491
29.1.2 OLED General Lighting in the Years
"2013-2020" 491
29.2 Haitz and Tsao Predictions for the Years "2010-2020" 492
29.3 Research Areas and Technical Challenges 494
29.3.1 Preventing Droop 494
29.3.2 GaN LED Substrates 495
29.3.3 Using Narrow-Band Red Phosphors 497
29.3.4 Eschewing Phosphor Heating by Stokes Shift 498
29.3.5 Closing the Red-to-Green Efficacy Gap 498
29.3.6 Suppressing the Flickering ofAC LED Lamps 498
29.3.7 Coating with a Reflective Plastic for Uniform
Light Dispersal 498
Contents xxiii
29.3.8 Improving White OLEDs to >100 lm/W
Efficiency 499
29.3.9 Replacing the Costly Indium in OLEDs 499
29.3.10 Designing Intelligent Luminaires 499
29.3.11 Formulating Lighting Standards 499
29.4 Moving beyond 2020 499
29.4.1 Haitz Prediction 49929.4.2 Tsao's Prediction 500
29.4.3 Closing Stages ofthe Lighting Revolution 500
29.5 Discussion and Conclusions 500References 501
Review Exercises 503
Chapter 30 Laser Diode and Laser Diode-Based Lighting 505
Learning Objectives 50530.1 Light-Emitting and Laser Diodes 505
30.2 Homojunction Laser Diode 506
30.2.1 Conditions for Stimulated Emission 50830.2.2 Operation 51030.2.3 Drawbacks 510
30.3 Heterojunction Laser Diode 511
30.3.1 Carrier Confinement 51230.3.2 Optical Confinement 51230.3.3 Stripe Geometry 51330.3.4 Output Spectrum and Characteristics 513
30.4 Theory of Laser Diode 51430.4.1 Gain Coefficient (a) 514
30.4.2 Loss Coefficient (ar) 51430.4.3 Transparency Current DensityJ0 515
30.4.4 Threshold Current Density 51630.4.5 Output Power of the Laser 519
30.5 From LED to Laser Diode-Based Lighting 52130.5.1 Efficiency of Laser Diode at High Currents 521
30.5.2 Laser Diode-Based Lighting Methods 52230.5.3 Short-Term Possibility 522
30.5.4 Long-Term Possibility 52330.6 Discussion and Conclusions 525
References 527Review Exercises 527
Appendix 1: Mathematical Notation—English Alphabet Symbols 529
Appendix 2: Mathematical Notation—GreekAlphabet Symbols 535
Appendix 3: Chemical Symbols and Formulae 539
Index 545