IEEE PULSE presents

Fundamentals of Solid-State Lighting: LEDs, OLEDs, and Their Applications in Illumination and Displays

Book Reviews March/April 2020
Author: Paul King

Edited by Vinod Kumar Khanna, CRC Press/Taylor & Francis Group, Boca Raton, FL, 2014, ISBN: 13-978-1-4665-6109-0, xxxix + 563 pages, US$163

 

Although this book is aimed primarily at electrical and electronics engineers, it can also be useful for all technical professionals who, in one way or another, are interested in lighting issues, especially those related to recent advances in light-emitting diode (LED) and organic-LED (OLED) technologies. This includes biomedical, civil, and industrial engineers, as well as architects, who may consider skipping some of the most specialized chapters of the book and focus on the (largely self-contained) sections devoted to LED and OLED lighting applications.

Part I (Chapters 1–4), on the history and basics of lighting, presents a brief historical survey of lighting technology as well as the fundamental concepts for conventional and LED lighting. Chapter 1 (Chronological History of Lighting) provides a brief but interesting history of lighting, from the Sun and fire to gas lighting, limelight, and incandescent lamps to fluorescent lamps and LEDs. The chapter includes a brief description of Haitz’s law, the counterpart to Moore’s law that projects the evolution of LEDs’ performance. Chapter 2 (Nature and Quality of Lighting) introduces general properties of light as derived from electromagnetic theory.  The physics of human vision and the main principles of photometry, colorimetry, and radiometry are discussed as well. This chapter is crucial for the analysis of optical sources and technologies in the following chapters and could prove a useful reference regarding the basics of vision and light measurement, despite some optical units being used in tables before they are presented in the main text. Chapter 3 (Conventional Light Sources) is devoted to the conventional light sources that LEDs have been replacing in recent years, or are expected to replace in the near future, such as incandescent filament bulbs, tungsten halogen lamps, mercury and sodium vapor lamps, and fluorescent tubes. Advantages and disadvantages of each illumination category, as well as (somewhat rough) sketches of the devices are provided. The fourth and last chapter of Part I (LED-Based Solid-State Lighting) introduces monochromatic LED lighting in terms of elementary band theory, as well as device structure. It also provides a general overview of the methods for light generation, as well as the main concepts, advantages, and disadvantages related to solid-state lighting.

Part II (Chapters 5–17) gives a detailed description of the science and engineering of inorganic LEDs. Light emission processes, specifically luminescence, as well as electron and hole recombination in semiconductors (both radiative and nonradiative) are presented in Chapter 5 (Physical Principles of Inorganic LEDs). The following two chapters, on homojunction and heterojunction LEDs, respectively, describe the main features of both types of devices as classified in terms of their structure, whereas Chapter 8 (Surface- and Edge-Emitting LEDs) is devoted to describing LEDs in terms of the orientation of the output light beam and also includes a section on superluminescent LEDs. Chapter 9 (Light Extraction from LEDs) analyzes the methods to overcome the total-internal-reflection problems arising at semiconductor–air interfaces, as well as substrate absorption of light, which constrains LED efficiency. This involves different choices to be made regarding structures, materials, and even textures.

The following few chapters emphasize the electronic-device nature of inorganic LEDs. Chapter 10 (Semiconductor Materials for Inorganic LEDs) is devoted to the relevant factors for choosing optoelectronic materials and the most important families to which they belong. Processes for LED manufacturing, including substrate fabrication, liquid-phase epitaxy, and metal organic chemical vapor deposition, as well as packaging techniques such as injection and molding and surface mounting, are introduced in Chapters 11 (Fabrication of Inorganic LEDs) and 12 (Packaging of LEDs). Chapter 12 also presents a few technologies borrowed from MEMS fabrication. Implications of these technologies in terms of thermal performance and reliability are also discussed. The above chapters provide the background for a discussion on LED performance parameters, which may be used to compare devices from different manufacturers, in Chapter 13. Thermal management of LEDs and related issues affecting a LED’s lifetime and performance are considered in Chapter 14.

Chapter 15 (White Inorganic LEDs) provides a detailed discussion about the general approaches for generating good-quality white light for lighting applications, which leads directly to the discussion on phosphor materials for LEDs in Chapter 16. These materials (usually ceramics, many of them containing rare earths but only occasionally containing phosphorus) provide additional wavelengths that permit the generation of white light from low-wavelength light sources. Part II ends with high-brightness LEDs in Chapter 17, which are those capable of high-luminance levels of the type required in extensive illumination, rather than in screens or indicators. This implies special design issues involving particular device architectures, thicknesses, and thermal management.

Part III (Chapters 18–20) presents organic LEDs and is one of the most notable contributions of the book, given the relative scarcity of college-level books on this relatively new technology and the increasing importance of OLEDs in new consumer products. Chapter 18 (Organic Semiconductors and Small-Molecule LEDs) provides a general overview on OLED materials, as well as the typical molecules and structures used for light production and their optical properties as arising from the interaction of molecular orbitals. Polymer LEDs are presented in Chapter 19 (Polymer LEDs), including the differences arising from using large organic molecules instead of the shorter ones presented in the previous chapter. Several tables are used to compare the different types of LEDs and may be useful when making decisions about the adoption of these technologies. Chapter 20 (White Organic LEDs) describes different approaches for the generation of light with organic materials, including excimers and electromers, among others. Structural approaches for device construction, such as the use of vertical or horizontal RGB stacks combining red, green, and blue light sources, are also discussed.

Part IV (Chapters 21 and 22), on LED driving circuits, focuses on voltage sources for LEDs, with DC sources such as batteries, regulators, and switch-mode power supplies discussed in Chapter 21 and AC sources, such as bridge rectifiers and buck converters, in Chapter 22. The emphasis in these chapters is on electrical circuits to drive LEDs, but some important issues, including power factor and total harmonic distortion, are also discussed.

Part V (Chapters 23–28) is devoted to applications of LEDs. Chapter 23 (LEDs in General Illumination) goes beyond general lightings (retrofit LED lamps, LED tube lights, and street illumination) to discuss such important niches as LED bulbs for cars, as well as performance parameters, including spectral distributions. The use of distributed light sources covering substantial areas, as opposed to point sources of light, is presented in Chapter 24 (Large-Area OLED Lighting). This includes topics such as OLED tiles and panels and flexible OLED devices, as well as remaining challenges related to short circuits, heat generation, and nonuniform light emission. Chapters 25 and 26 are devoted, respectively, to inorganic and organic LED displays. Such well-known devices as the 7- and 14-segment displays and LED arrays are a prelude to LED screens used in many flat TV sets nowadays. Passive matrix OLED (PMOLED) and active matrix OLED (AMOLED) displays are contrasted in terms of their particular advantages and disadvantages before the introduction of thin-film transistor (TFT) backplane technologies. Chapter 27 (Miscellaneous Applications of Solid-State Lighting) includes such topics as traffic lights, fiber optic, and optical wireless communications, as well as horticultural applications; it also includes a brief section on medical applications of LEDs that many biomedical engineers will find interesting, at least as a leader to more advanced sources of information. Finally, the use of sensors and control devices to adapt lighting to changing requirements (as may be necessary in, say, night illumination or when considering security issues) is discussed in Chapter 28 (Smart Lighting).

Lastly, Part VI (Chapters 29 and 30) treats the future of lighting. In particular, chapter 29 (Opportunities and Challenges of Solid-State Lighting) provides a series of projections and technology forecasts that illuminate us about where the future markets for solid-state lighting may be, as well as current difficulties that may need to be overcome. Although the book was written in 2014, it also includes predictions for beyond 2020. Chapter 30 discusses the theory and operation principles of laser diodes (LDs), puts them in contrast with LEDs, and discusses how LDs may be used as illumination sources in the short and long terms.

The book also includes two appendixes on mathematical notation, one providing the nomenclature for English-alphabet symbols and another one for Greek-alphabet symbols. A third appendix provides the formulas and names of the chemical elements and compounds used in the text.

There are some areas for improvement for this book. The book could profit from improving the quality of its images, many of which seem to have been prepared with rather primitive graphics editors. The citation scheme of some references, particularly web pages with very long URL names, could be modified to enhance readability in some chapters.

Nevertheless, this book also has several strengths. Numerous quantitative examples are presented throughout the book to show the determination of relevant parameters for each device or for the solution of application problems. There is a discussion and conclusions section in each chapter that allows the student to focus on the most relevant points to remember, and most chapters include ingenious verses providing relaxation as well as useful opportunities for enhanced understanding and recall. Moreover, each chapter ends with a series of review exercises to permit further analysis of the key concepts and ideas.

A very useful feature of this textbook is its inclusion of learning objectives at the beginning of every chapter, which allows both students and instructors to identify the most relevant portions of the book to read according to their particular needs. Its division into short sections enhances its readability, while allowing for an in-depth coverage of the relevant topics. All in all, this may be a quite useful textbook for undergraduate students in their junior or senior years, as well as first-year graduate students.

—Review by José R. Alvarez-Bada, Universidad Anáhuac México, North Campus

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