Table of Contents

Cover

Series page

Title page

Copyright page

Dedication

Figures

Preface

THE LIGHTING REVOLUTION

THE LAST VACUUM TUBE

GREEN LIGHTING

A LIFETIME OF LIGHTING

LIGHTING THE WORLD WITH LEDS

Chapter 1 Practical Introduction to LEDs

WHAT IS AN LED?

SMALL LEDS VERSUS POWER DEVICES

PHOSPHORS VERSUS RGB

INSIDE AN LED

IS AN LED RIGHT FOR MY APPLICATION?

HAITZ’S LAW(S)

THE WILD WEST

LEDS AND OLEDS AND …?

Chapter 2 Light Bulbs and Lighting Systems

LIGHT SOURCES

CHARACTERISTICS OF LIGHT SOURCES

TYPES OF BULBS

HISTORY OF LIGHTING

GOVERNMENTS

LIGHTING SYSTEMS

Chapter 3 Practical Introduction to Light

THE POWER OF LIGHT

RADIOMETRIC VERSUS PHOTOMETRIC

LUMINOUS INTENSITY, ILLUMINANCE, AND LUMINANCE (OR CANDELA, LUX, AND NITS)

WHAT COLOR WHITE?

COLOR RENDITION: HOW THE LIGHT LOOKS VERSUS HOW OBJECTS LOOK

Chapter 4 Practical Characteristics of LEDs

CURRENT, NOT VOLTAGE

FORWARD VOLTAGE

REVERSE BREAKDOWN

NOT EFFICIENCY—EFFICACY!

LED OPTICAL SPECTRA

OVERDRIVING LEDS

KEY DATASHEET PARAMETERS

BINNING

THE TOLERANCE GAME

Chapter 5 Practical Thermal Performance of LEDs

MECHANISMS BEHIND THERMAL SHIFTS

ELECTRICAL BEHAVIOR OF LEDS WITH TEMPERATURE

OPTICAL BEHAVIOR OF LEDS WITH TEMPERATURE

OTHER PERFORMANCE SHIFTS WITH TEMPERATURE

LED LIFETIME: LUMEN DEGRADATION

LED LIFETIME: CATASTROPHIC FAILURE

PARALLELING LEDS

Chapter 6 Practical Thermal Management of LEDs

INTRODUCTION TO THERMAL ANALYSIS

CALCULATION OF THERMAL RESISTANCE

THE AMBIENT

PRACTICAL ESTIMATION OF TEMPERATURE

HEAT SINKS

FANS

RADIATION ENHANCEMENT

REMOVING HEAT FROM THE DRIVE CIRCUITRY

Chapter 7 Practical DC Drive Circuitry for LEDs

BASIC IDEAS

BATTERY BASICS

OVERVIEW OF SMPS

BUCK

BOOST

BUCK-BOOST

INPUT VOLTAGE LIMIT

DIMMING

BALLAST LIFETIME

ARRAYS

Chapter 8 Practical AC Drive Circuitry for LEDs

SAFETY

WHICH AC?

RECTIFICATION

TOPOLOGY SELECTION

NONISOLATED CIRCUITRY

ISOLATION

COMPONENT SELECTION

EMI

POWER FACTOR CORRECTION

LIGHTNING

DIMMERS

RIPPLE CURRENT EFFECTS ON LEDS

LIFETIME

UL, ENERGY STAR, AND ALL THAT

Chapter 9 Practical System Design With LEDs

PCB DESIGN

GETTING THE LIGHT OUT

LEDS IN HARSH ENVIRONMENTS

DESIGNING WITH THE NEXT GENERATION LED IN MIND

LIGHTING CONTROL

Chapter 10 Practical Examples

EXAMPLE: DESIGNING AN LED FLASHLIGHT

EXAMPLE: DESIGNING A USB LIGHT

EXAMPLE: DESIGNING AN AUTOMOBILE TAILLIGHT

EXAMPLE: DESIGNING AN LED LIGHT BULB

Chapter 11 Practical Measurement of LEDs and Lighting

MEASURING LIGHT OUTPUT

LED MEASUREMENT STANDARDS

MEASURING LED TEMPERATURE

MEASURING THERMAL RESISTANCE

MEASURING POWER, POWER FACTOR, AND EFFICIENCY

ACCELERATED LIFE TESTS

Chapter 12 Practical Modeling of LEDs

PRELIMINARIES

PRACTICAL OVERVIEW OF SPICE MODELING

WHAT NOT TO DO

WHAT TO DO

MODELING FORWARD VOLTAGE

REVERSE BREAKDOWN

MODELING OPTICAL OUTPUT

MODELING TEMPERATURE EFFECTS

MODELING THE THERMAL ENVIRONMENT

A THERMAL TRANSIENT

SOME COMMENTS ON MODELING

References

Index

IEEE Press Series on Power Engineering

Color Plates

IEEE Press

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IEEE Press Editorial Board

Lajos Hanzo, Editor in Chief

R. Abari | M. El-Hawary | S. Nahavandi
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F. Canavero | M. Lanzerotti | T. Samad
T. G. Croda | O. Malik | G. Zobrist

Kenneth Moore, Director of IEEE Book and Information Services (BIS)

Copyright © 2011 the Institute of Electrical and Electronics Engineers, Inc. All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey

Published simultaneously in Canada

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Library of Congress Cataloging-in-Publication Data:

Lenk, Ron, 1958–

Practical lighting design with LEDs / by Ron Lenk, Carol Lenk.

p. cm. – (IEEE Press series on power engineering ; 67)

ISBN 978-0-470-61279-8

 1. Light emitting diodes. 2. Electric lamps–Design and construction. 3. Electric lighting–Design. I. Lenk, Carol. II. Title.

TK7871.89.L53L46 2011

621.32–dc22

2010048267

oBook ISBN: 978-1-118-00821-8

ePDF ISBN: 978-1-118-00820-1

ePub ISBN: 978-1-118-01173-7

To our children, for being so patient

Figures

Figure 1.1 T1¾ (5 mm) LEDs

Figure 1.2 Fluorescent Tube’s Spectral Power Distribution

Figure 1.3 LEDs Can Be Used Everywhere

Figure 1.4 Haitz’s Law

Figure 2.1 Currents in a Fluorescent Tube

Figure 2.2 Various Bulb Shapes

Figure 3.1 The Electromagnetic Spectrum

Figure 3.2 Scotopic Vision is much more Sensitive than Photopic Vision

Figure 3.3 Emission Spectra of Four Common Light Sources

Figure 3.4 Solar Radiation Spectrum

Figure 3.5 One Steradian Intersects 1 m² of Area of a 1 m Radius Ball

Figure 3.6 Solid Angle in Steradians versus Half Beam Angle in Degrees

Figure 3.7 Definition of Beam Angle

Figure 3.8 Typical Lambertian Radiation Pattern

Figure 3.9 Dimensions for a USB Keyboard Light Design

Figure 3.10 Spectra of Neutral-White and Warm-White LEDs

Figure 3.11 CIE 1931 (x, y) Chromaticity Space, Showing the Planck Line and Lines of Constant CCT

Figure 3.12 (x, y) Chromaticity Diagram Showing CCT and 7-Step MacAdam Ellipses

Figure 3.13 Cool White Fluorescent 4100 K, CRI 60; Incandescent, 2800 K, CRI 100; Reveal® Incandescent 2800 K, CRI 78

Figure 3.14 Approximate Munsell Test Color Samples

Figure 3.15 Circadian Rhythm Sensitivity

Figure 3.16 Identical Gray Boxes Look Different Depending on Their Background

Figure 4.1 Reverse Bias Protection

Figure 4.2 LEDs with Reverse Bias Protection

Figure 4.3 Light Output as a Function of Current

Figure 4.4 Forward Voltage as a Function of Current

Figure 4.5 Efficacy versus Drive Current

Figure 4.6 Light Output as a Function of Wavelength

Figure 4.7 Many LEDs Have Poor R9

Figure 4.8 (x, y) as a Function of Current

Figure 4.9 Different Output Light Distributions Are Available

Figure 4.10 Neutral-White Bin Structure

Figure 5.1 Brightness as a Function of Temperature

Figure 5.2 LED Temperature Profile for Parameters Given in Text

Figure 5.3 Forward Voltage as a Function of Current

Figure 6.1 Thermal Model for LED Example

Figure 6.2 Thermal Model of Two Parallel Thermal Paths

Figure 6.3 LED Temperature as a Function of Time

Figure 6.4 There Are Many Thermal Paths to Ambient

Figure 6.5 Estimating Temperature Rise from Power Density

Figure 6.6 An LED Heat Sink

Figure 7.1 12 V Battery I-V Curve

Figure 7.2 Alkaline-Cell Battery Voltage as a Function of Time with a Resistive Load

Figure 7.3 Operating a Transistor in Linear Mode Is Inefficient

Figure 7.4 When the Transistor Is On, Current in the Inductor Increases; When the Transistor Is Off, Current in the Inductor Decreases

Figure 7.5 LM3405 Schematic for Buck

Figure 7.6 FAN5333A Schematic for Boost

Figure 7.7 HV9910 Schematic for Buck-Boost

Figure 7.8 Pulse Width Modulation Turns the Current Rapidly On and Off to Get an Average Current

Figure 7.9 Dimming Circuit

Figure 7.10 The Effect of the Current Sense Resistor Is Compensated by Putting One in Series with Each String

Figure 7.11 LED Forward Voltage Variation Can Be Compensated at the Cost of Additional Power

Figure 7.12 Ballasting LED Strings with Total Current Sensing

Figure 8.1 Block Diagram of AC SMPS for LED Lighting

Figure 8.2 A Bridge Rectifier

Figure 8.3 Half-wave Rectification

Figure 8.4 Reducing the Ripple from a Bridge Rectifier with a Capacitor

Figure 8.5 Running LEDs Directly Off-Line

Figure 8.6 How the Off-Line Buck Works

Figure 8.7 A Nonisolated Off-Line LED Driver

Figure 8.8 Adding a Transformer Makes the Converter into a Forward

Figure 8.9 Adding a Transformer Makes the Converter into a Flyback

Figure 8.10 Protecting the HV9910 from High Voltages

Figure 8.11 Resistors Balance Voltages for Series Capacitors

Figure 8.12 Normal Mode EMI Filtering for a Two-Wire Input

Figure 8.13 Common Mode EMI Filtering Added for a Three-Wire Input

Figure 8.14 Current Loops May Cause EMI Problems; Reducing Loop Area Helps

Figure 8.15 A Big Capacitor Maintains Constant Voltage During the Line Cycle, Generating Large Peak Currents and Bad Power Factor

Figure 8.16 A Smaller and Cheaper PFC

Figure 8.17 Simple Power Factor Correction Circuit

Figure 8.18 Adding an MOV to the Design Protects It Moderately Well from Lightning

Figure 8.19 Output Waveform of a Triac Dimmer

Figure 8.20 Keeping an IC’s Power Alive During the Off-Time of a Dimmer

Figure 8.21 As Ripple Current Increases, Power Loss in the LED Also Increases

Figure 8.22 Forward Voltage Increases with Increasing Current

Figure 8.23 Increasing the Current Does Not Proportionally Increase the Light

Figure 8.24 200 mApp Ripple Current on a 350 mA DC Drive

Figure 9.1 A Schematic which Could Be Improved

Figure 9.2 A Good Schematic

Figure 9.3 Poor Grounding Layout and Improved Layout

Figure 9.4 Soda-Lime Glass Optical Transmission

Figure 9.5 DALI Topologies

Figure 10.1 FAN5333A Schematic for Flashlight

Figure 10.2 FAN5333A Final Schematic for Flashlight

Figure 10.3 Thermal Model

Figure 10.4 PCB for LED Flashlight Ballast

Figure 10.5 First-Cut USB Light Schematic

Figure 10.6 LM3405 Schematic for USB Light

Figure 10.7 USB Light PCB, Top View and X-Ray Bottom View

Figure 10.8 Final USB Light Schematic

Figure 10.9 HV9910 Schematic for Taillight

Figure 10.10 LS E63F I-V Curve

Figure 10.11 Final HV9910 LED Automobile Taillight Schematic

Figure 10.12 LED Taillight: Whole Board, Topside Zoom of Ballast Area, Bottom Side X-Ray Zoom of Ballast Area

Figure 10.13 BR Bulbs

Figure 10.14 Initial Thermal Model for BR40

Figure 10.15 First Attempt at a BR Design

Figure 10.16 Final HV9910 Schematic for LED BR40

Figure 10.17 BR40 PCB: Topside and Bottom Side with X-Ray Vision

Figure 11.1 Typical Lux Meter

Figure 11.2 Sketch of Operation of an Integrating Sphere

Figure 11.3 Walk-in Integrating Sphere

Figure 11.4 Gooch & Housego 6-Inch Integrating Sphere with OL770-LED Spectroradiometer

Figure 11.5 Location of Thermocouple to Measure LED Temperature

Figure 11.6 High Current Drawn at AC Line Peak Gives a High Crest Factor

Figure 11.7 Phase Shift between Current and Voltage Also Gives Low Power Factor

Figure 12.1 Luxeon Rebel I-V Curve

Figure 12.2 First Model of Luxeon Rebel

Figure 12.3 Setting the GMIN Option to 1.0E-20 Fixes the Current at 0 V

Figure 12.4 LED Model Including Reverse Breakdown

Figure 12.5 With the Breakdown Modeled, the Complete I-V Curve Is Shown

Figure 12.6 Normalized Light Output versus Current

Figure 12.7 Data versus Equation for Optical Output versus Drive Current

Figure 12.8 LED Model with Light Output, Temperature Not Yet Included

Figure 12.9 The Effect of Temperature on Light Output

Figure 12.10 LED Model with Temperature Effect on Both Forward Voltage and Optical Output

Figure 12.11 Complete LED Model

Figure 12.12 The Thermal Response of Two LEDs to Current Pulse

Figure 12.13 The Optical Response of Two LEDs to Current Pulse

Preface

THE LIGHTING REVOLUTION

LEDs are bringing in a new era in lighting. Similar to the evolution of computing power that computers went through, from vacuum tubes to the silicon-based semiconductor brains of modern-day computers, lighting is now poised to ride an exponential growth wave in efficacy. From oil lamps to the invention of the Edison light bulb 100 years ago to the fluorescent lights of 50 years ago to the LEDs of today, lighting technology is finally joining the modern world of solid-state technology.

In the near term, LED-based lighting will increasingly become the efficient light source of choice, replacing both incandescent and fluorescents. The hurdles that keep consumers from adopting present-day energy efficient lighting, such as shape, color quality, the presence of toxic mercury, and limited lifetime, are all better addressed by LEDs.

In the long term, LED-based lighting will be better and cheaper than every other light source. It will become the de facto light of choice. LED lighting will be cheap, efficient, and used in ways that haven’t been imagined yet. It will transform the $100 billion lighting industry, and with transformation comes opportunity.

THE LAST VACUUM TUBE

Lighting is the last field that still uses vacuum tubes. All electronics today use integrated circuits because of the enormous benefits in performance and cost. But an incandescent bulb is a type of vacuum tube, and so is a fluorescent bulb. LEDs are solid-state devices, the same as the rest of electronics. The amount of light that an LED can convert from 1 W of power is already on par with the best fluorescent tubes. The future is even brighter as LEDs are anticipated to double that performance in the next decade, and then go on to reach the physical limits of electricity to light conversion. We look forward to seeing the last ceiling-mounted vacuum tube in the not-too-distant future.

GREEN LIGHTING

The benefits of using LEDs for lighting are many. The most obvious is their efficiency. Lighting accounts for 20% of total electricity use throughout the world today. Using LEDs could cut this down to 4% or less. As LEDs become the dominant light source over the next decade, the reduction of energy used and greenhouse gases emitted will benefit everyone. Consumers will save hundreds of dollars every year from reduced energy use. Building owners will save even more. Utilities will be better equipped to manage growth. And the earth will experience the accumulation of fewer greenhouse gases, as well as a reduction in the emission of toxic mercury found in fluorescent lighting.

A LIFETIME OF LIGHTING

As solid-state devices, LEDs have extremely long lifetimes. They have no filaments to break. They can’t leak air into their vacuum because they don’t use a vacuum. In fact, they don’t really break at all; they just very gradually get dimmer. Imagine changing your light bulb only once or twice in your entire lifetime!

LIGHTING THE WORLD WITH LEDS

Just as microprocessors got cheaper and more powerful, LEDs will also benefit from the cost-reduction techniques developed in the semiconductor industry. LED light prices will eventually decrease to be on par with incandescent bulbs. Taken together with LEDs’ reduced energy usage, this will enable the universal availability of lighting. Imagine every child in the poorest village having a light to read by.

The design of LED-based lighting systems is an exciting field, but they are fairly technical devices. With this book, we hope to enable the reader to do great things with lighting, both for him- or herself and for the world.

RON LENK

CAROL LENK

Woodstock, Georgia

February 2011

Chapter 1

Practical Introduction to LEDs

Light bulbs are everywhere. There are over 20 billion light bulbs in use around the world today. That’s three for each person on the planet! We expect that within the next 10 years, the majority of these bulbs will be light emitting diodes (LEDs). This is because LEDs can provide efficiency dozens of times higher than incandescent light bulbs. They can be as efficient as the theoretical limit for electricity to light conversion set by physics. This book is all about the practical aspects of LEDs and how you can make practical lighting designs using them.

WHAT IS AN LED?

The purpose of this book is to tell you practical things about LEDs. So in this section, we’re not going to regale you with jargon about “direct bandgap GaInP/GaP strained quantum wells” or such. Let’s directly address the question, What is an LED?

The name “light emitting diode” tells you a lot already. In the first place, the noun tells you that it’s a diode. A diode conducts current in one direction and not the other. And that’s what an LED does. While we’ll explore the details of its electrical behavior in Chapter 4, the only thing to note for the moment is that it has a much higher forward voltage than the diodes usually used in electronics. While a 1N4148 has a drop of about 700 mV, an LED may drop 3.6 V. This is because LEDs are not made from silicon, but from other semiconductors. But other than that, an LED’s electrical characteristics are very much like those of other diodes.

The words “light-emitting” tell you a lot more. Now all diodes emit at least a little bit of light. You can open up an integrated circuit (IC) and use a scanner to see which parts of the circuit are emitting light. This tells you which parts are conducting current. IC designers use this to help debug their ICs. However, the amount of light emitted by ICs is very small. Since the purpose of LEDs is to emit light, they have been carefully designed to optimize this performance. That’s why, for example, they have a much higher forward voltage than normal, rectifier diodes. Rectifiers have been optimized to minimize their forward voltage while maximizing reverse breakdown voltage. LEDs are optimized to produce the most light of the right color at the lowest power, and things such as forward voltage (by itself) don’t matter. Of course, forward voltage does enter into how much power the LED dissipates, and we’ll see in Chapter 5 how to characterize the light emitted versus the power dissipated.

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!