Illumination Engineering

Design with Nonimaging Optics

R. John Koshel, R. John Koshel

• Publisher: Wiley-IEEE Press
• Year: 2012
• ISBN:
  9781118462454
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

This book brings together experts in the field who present material on a number of important and growing topics including lighting, displays, solar concentrators.The first chapter provides an overview of the field of nonimagin and illumination optics. Included in this chapter are terminology, units, definitions, and descriptions of the optical components used in illumination systems. The next two chapters provide material within the theoretical domain, including etendue, etendue squeezing, and the skew invariant. The remaining chapters focus on growing applications.

This entire field of nonimaging optics is an evolving field, and the editor plans to update the technological progress every two to three years.The editor, John Koshel, is one of the most prominent leading experts in this field, and he is the right expert to perform the task.

CHAPTER 1

INTRODUCTION AND TERMINOLOGY

John Koshel

This chapter introduces the reader to a number of terms and concepts prevalent in the field of illumination optics. I establish the units basis that is used throughout this book. The fields of nonimaging and illumination optics have a fundamental basis on these units; therefore, it is demanded that the reader be well versed in units and how to design, analyze, and measure with them. Next, I give an overview of the field and important parameters that describe the performance of an illumination system. The next chapter on étendue expands upon this treatment by introducing terms that are primarily focused on the design of efficient illumination systems.

1.1 WHAT IS ILLUMINATION?

Until recently the field of optical design was synonymous with lens or imaging system design. However, within the past decade, the field of optical design has included the subfield of illumination design. Illumination is concerned with the transfer of light, or radiation in the generic sense,* from the source(s) to the target(s). Light transfer is a necessity in imaging systems, but those systems are constrained by imaging requirements. Illumination systems can ignore the “imaging constraint” in order to transfer effectively the light. Thus, the term nonimaging optics is often used. In the end, one may classify optical system design into four subdesignations:

• Imaging Systems. Optical systems with the imaging requirement built into the design. An example is a focal-plane camera.
• Visual Imaging Systems. Optical systems developed with the expectation of an overall imaging requirement based upon integration of an observation system. Examples include telescopes, camera viewfinders, and microscopes that require human observers (i.e., the eye) to accomplish imaging.
• Visual Illumination Systems. Optical systems developed to act as a light source for following imaging requirements. Examples include displays, lighting, and extend to the illuminator for photocopiers.
• Nonvisual Illumination Systems. Optical systems developed without the imaging criterion imposed on the design. Examples include solar concen­trators, optical laser pump cavities, and a number of optical sensor applications.

The latter two systems comprise the field of illumination engineering. Imaging systems can be employed to accomplish the illumination requirements, but these systems are best suited for specific applications. Examples include critical and Köhler illumination used, for example, in the lithography industry, but as this book shows, there are a number of alternative methods based on nonimaging optics principles. This book focuses on these nonimaging techniques in order to transfer light effectively from the source to the target, but imaging principles are used at times to improve upon such principles. Additionally, I place no requirement on an observer within the system, but as you will discover, most illumination optics are designed with observation in mind, including the human eye and optoelectronic imaging, such as with a camera. To neglect the necessary visualization and its characteristics often has a detrimental effect on the performance of the illumination system. This last point also raises the subjective perception of the illumination system design. This factor is not currently a focus of this book, but it is discussed in order to drive the development of some systems.

I use the remainder of this chapter to discuss:

• A short history of the illumination field
• The units and terminology for illumination design and analysis
• The important factors in illumination design
• Standard illumination optics
• The steps to design an illumination system
• A discussion of the difficulty of illumination design, and
• The format used for the chapters presented herein.

Note that I typically use the terms illumination and nonimaging interchangeably, but, in fact, illumination is a generic term that includes nonimaging and imaging methods for the transfer of light to a target.

1.2 A BRIEF HISTORY OF ILLUMINATION OPTICS

The history of the field of illumination and nonimaging optics is long, but until recently it was mostly accomplished by trial and error. Consider Figure 1.1, which shows a timeline of the development of sources and optics for use in the illumination field [1]. Loosely, the field of illumination optics starts with the birth of a prevalent light source on earth—the Sun. While the inclusion of the Sun in this timeline may at first appear facetious, the Sun is becoming of increasing importance in the illumination and nonimaging optics communities. This importance is borne out of daylighting systems, solar thermal applications, and solar energy generation. The use, modeling, and fabrication of sources is one of the largest components of the field of illumination design. Increasingly, LED sources are supplanting traditional sources since LEDs provide the potential for more efficient operation, color selection, long lifetimes, and compact configurations. It is only in the past 60 years that nonimaging optical methods have been developed. The illumination industry, both in design and source development, is currently burgeoning, so vastly increased capabilities are expected in the next few decades.

Figure 1.1 A timeline of the history of illumination and nonimaging optics. On the left is the approximate date of inception for the item on the right. Items listed in blue are illumination optic design concepts, those leading with LED are new solid-state lighting sources, and the remainder is other types of sources.

1.3 UNITS

As with any engineering or scientific discipline, the use of units is imperative in the design and modeling of illumination systems. It is especially important to standardize the system of units in order to disseminate results. There are essentially two types of quantities used in the field of illumination:

• Radiometric Terms. Deterministic quantities based on the physical nature of light. These terms are typically used in nonvisual systems; and
• Photometric Terms. Quantities based on the human visual system such that only visible electromagnetic radiation is considered. This system of units is typically used in visual systems.

Radiometric and photometric quantities are connected through the response of eye, which has been standardized by the International Commission on Illumination (Commission Internationale de L′Éclairage; CIE) [2, 3]. Both of these set of terms can be based on any set of units, including English and metric; however, standardization at the Fourteenth General Conference on Weights and Measures in 1971 on the metric system is defined by the International System (Système Internationale; SI) [4]. The units for length (meter; m), mass (kilogram; kg), and time (second; s) provide an acronym for this system of units: MKS. There is an analogous one that uses the centimeter, gram, and second, denoted as CGS. This book uses the MKS standard for the radiation quantities, though it often makes use of terms, especially length, in non-MKS units, such as the millimeter. In the next two subsections, the two set of terms are discussed in detail. In the section on photometric units, the connection between the two systems is presented.

1.3.1 Radiometric Quantities

Radiometry is a field concerned with the measurement of electromagnetic radiation. The radiometric terms as shown in Table 1.1 are used to express the quantities of measurement* [5]. The term radiant is often used before a term, such as radiant flux, to delineate between like terms from the photometric quantities; however, the accepted norm is that the radiometric quantity is being expressed if the word radiant is omitted. Additionally, radiometric quantities are often expressed with a subscript “e” to denote electromagnetic. Omission of this subscript still denotes a radiometric quantity.

TABLE 1.1 Radiometric Terms and their Characteristics

Radiometric quantities are based on the first term in the table, radiant energy (Q...

Table of contents

• COVER
• IEEE PRESS
• TITLE PAGE
• COPYRIGHT PAGE
• DEDICATION
• PREFACE
• CONTRIBUTORS
• GLOSSARY
• CHAPTER 1 INTRODUCTION AND TERMINOLOGY
• CHAPTER 2 ÉTENDUE
• CHAPTER 3 SQUEEZING THE ÉTENDUE
• CHAPTER 4 SMS 3D DESIGN METHOD
• CHAPTER 5 SOLAR CONCENTRATORS
• CHAPTER 6 LIGHTPIPE DESIGN
• CHAPTER 7 SAMPLING, OPTIMIZATION, AND TOLERANCING
• INDEX