Practical Lighting Design With LEDs

Transcription

1 Practical Lighting Design With LEDs Ron Lenk Carol Lenk J IEEE PRESS SERIES u POWER ENGINEERING Mohamed E. El-Hawary, Series Editor IEEE PRESS WILEY A John Wiley & Sons, Inc., Publication

2 Contents Figures Preface xiii xvü 1 Practical Introduction to LEDs l What Is an LED? 1 Small LEDs versus Power Devices 2 Phosphors versus RGB 3 Inside an LED 4 Is an LED Right for My Application? 6 Haitz's Law(s) 8 The Wild West 10 LEDs and OLEDs and...? 11 2 Light Bulbs and Lighting Systems 13 Light Sources 13 Incandescent 13 Halogen 14 Fluorescent 14 Induction Lighting 15 High Intensity Discharge (HID) Lamps 15 Characteristics of Light Sources 16 Light Quality 16 Efficacy 17 Timing 17 Dimming 18 Aging 19 Types of Bulbs 19 Bulb Shapes 19 Bulb Bases 21 Specialty Bulbs 21 vii

3 vüi Contents History of Lighting 22 Governments 23 Lighting Systems 23 3 Practical Introduction to Light 27 The Power of Light 27 Background: Light as Radiation 27 Radiometric versus Photometric 28 Luminous Intensity, Illuminance, and Luminance (or Candela, Lux, and Nits) 32 Luminous Intensity 32 Illuminance 34 Luminance 36 Summary of Amount of Light 37 What Color White? 37 MacAdam Ellipses 39 A Note about Color Space Standards 41 Color Rendition: How the Light Looks versus How Objects Look 41 The Human Factor 43 4 Practical Characteristics of LEDs 47 Current, Not Voltage 47 Forward Voltage 48 Reverse Breakdown 49 Not Efficiency Efficacy! 51 LED Optical Spectra 54 Overdriving LEDs 57 Key Datasheet Parameters 58 Binning 58 The Tolerance Game 60 5 Practical Thermal Performance of LEDs 61 Mechanisms Behind Thermal Shifts 61 Electrical Behavior of LEDs With Temperature 62 Optical Behavior of LEDs With Temperature 63 Other Performance Shifts With Temperature 64 LED Lifetime: Lumen Degradation 66 LED Lifetime: Catastrophic Failure 67 Paralleling LEDs 67

4 Contents ix 6 Practical Thermal Management of LEDs 71 Introduction to Thermal Analysis 71 Calculation of Thermal Resistance 72 The Ambient 74 Practical Estimation of Temperature 75 Heat Sinks 76 Fans 78 Radiation Enhancement 79 Removing Heat from the Drive Circuitry 79 7 Practical DC Drive Circuitry for LEDs 81 Basic Ideas 81 Battery Basics 82 Overview of SMPS 85 Buck 86 Boost 88 Buck-Boost 89 Input Voltage Limit 91 Dimming 92 Ballast Lifetime 94 Arrays 95 8 Practical AC Drive Circuitry for LEDs 99 Safety 99 Which AC? 101 Rectification 103 Topology Selection 106 Nonisolated Circuitry 109 Isolation 110 Component Selection 112 EMI 114 Power Factor Correction 117 Lightning 119 Dimmers 120 Ripple Current Effects on LEDs 122 Lifetime 125 UL, Energy Star, and All That Practical System Design With LEDs 131 PCB Design 131 Getting the Light Out 136

5 x Contents LEDs in Harsh Environments 139 Designing With the Next Generation LED in Mind 141 Lighting Control 142 DALI Protocol 142 DMX512 Protocol and ZigBee Open-Standard Technology 143 Powerline Communication Practical Examples 145 Example: Designing an LED Flashlight 145 Initial Marketing Input 145 Initial Analysis 146 Specification 148 Power Conversion 150 Thermal Model 153 PCBs 155 Final Design 156 Example: Designing a USB Light 157 Initial Marketing Input 157 Initial Analysis 157 Specification 158 Power Conversion 159 Thermal Model 161 PCB 163 Final Design 163 Example: Designing an Automobile Taillight 165 Initial Marketing Input 165 Initial Analysis 165 Specification 167 Power Conversion 167 Thermal Model 172 PCB 172 Final Design 174 Example: Designing an LED Light Bulb 175 Initial Marketing Input 175 Initial Analysis 175 Specification 178 Power Conversion 181 PCBs 184

6 Contents xi 11 Practical Measurement of LEDs and Lighting 187 Measuring Light Output 187 Lux Meter 187 Integrating Sphere 189 Goniophotometer 192 Special Considerations in Measuring Light Output of LEDs 192 LED Measurement Standards 192 Luminaire Light Output (LM-79) 192 LED Lifetime (LM-80) 193 ASSIST 193 Measuring LED Temperature 194 Measuring Thermal Resistance 195 Measuring Power, Power Factor, and Efficiency 197 Accuracy versus Precision 197 Measuring DC Power 197 Measuring AC Power 200 Measuring Power Factor 201 Measuring Ballast Efficiency 201 EMI and Lightning 202 Accelerated Life Tests Practical Modeling of LEDs 207 Preliminaries 208 Practical Overview of Spice Modeling 209 What Not to Do 212 What to Do 213 Modeling Forward Voltage 214 Reverse Breakdown 219 Modeling Optical Output 221 Modeling Temperature Effects 224 Modeling the Thermal Environment 226 A Thermal Transient 228 Some Comments on Modeling 229 References 231 Index 233 IEEE Press Series on Power Engineering