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`INTRODUCTION
`TO OPTICS
`__ SecondEdition
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`Second Edition
`
`FRANK L. PEDROTTI, S.J.
`Marquette University
`Milwaukee, Wisconsin
`
`Vatican Radio,
`Rome
`
`LENO S. PEDROTTI
`Center for Occupational
`Research and Development
`Waco, Texas
`
`Emeritus Professor of Physics
`Air Force Institute of Technology
`Dayton, Ohio
`
`Introduction
`to Optics
`
`Prentice Hall, Upper Saddle River, New Jersey 07458
`
`

`

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`fl
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`Library of Congress Cataloging-in-Publication Data
`Pedrotti, Frank L., (date)
`‘ oe to optics/Frank L. Pedrotti, Leno S. Pedrotti.—
`ind
`ed.
`cm.
`.
`forbade bibliographical references and index.
`ISBN 0-13-501545-6
`1. Optics.
`I. Pedrotti, Leno S., (date).
`QC355.2.P43
`1993
`535—dc20
`
`Il. Title.
`92-33626
`cIP
`
`Acquisitions Editor: Ray Henderson
`Editorial/Production Supervision
`and Interior Design: Kathleen M.Lafferty
`Cover Designer: Joe DiDomenico
`Prepress Buyer: Paula Massenaro
`Manufacturing Buyer: Lori Bulwin
`Proofreader: Bruce D. Colegrove
`
`© 1993, 1987 by Prentice-Hall, Inc.
`UpperSaddle River, NewJersey 07458
`
`All rights reserved. No part of this book
`may be reproduced, in any form or by any means,
`without permission in writing from the publisher.
`
`————
`
`iil
`
`ISBN 0-13-501545-6
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`

`of the beam is also the radiance of the source, at the initial point of the beam, or
`Ly = L, = Lo.
`Suppose, referring to Figure 2-6, that we wish to know the quantity of radiant
`powerreaching an elementof area dA> on surface S$, due to the source element dA,
`on surface S;. The line joining the elemental areas, of length r;2, makes anglesof 0,
`
`
`
`Figure 2-6 Generalcase ofthe illumination of
`one surface by another radiating surface. Each
`elemental radiating area dA, contributes to each
`elementalirradiated area dA>.
`and @, with the respective normals to the surfaces, as shown. The radiant poweris
`d’®,», a second-orderdifferential because both the source and receptor are elemen-
`tal areas. By Eq. (2-7) or Eq. (2-8),
`
`2-3 PHOTOMETRY
`
`d’*®, =
`
`LdA;dAz cos 6; cos @>
`ry2
`
`and the total radiant poweratthe entire second surface due to the entire first surface
`is, by integration,
`
`(2-9)
`DO, = | | Sco2 ee
`ey
`Masa
`ri2
`By adding powersrather than amplitudesin this integration, we have tacitly assumed
`that the radiation source emits incoherentradiation. We shall say more about coher-
`ent and incoherentradiationlater.
`
`L cos 6; cos 62 dA; dA
`
`Radiometry applies to the measurementofall radiant energy. Photometry, on the
`other hand, applies only to the visible portion of the optical spectrum. Whereasra-
`diometry involves purely physical measurement, photometry takes into account the
`response of the humaneye to radiantenergy at various wavelengths and so involves
`psycho-physical measurements. Thedistinction rests on the fact that the human eye,
`as a detector, does not have a “flat” spectral rsponse; that is,
`it does not respond
`with equalsensitivity at all wavelengths. If three sources of light of equal radiant
`powerbut radiating blue, yellow, and red light, respectively, are observed visually,
`the yellow source will appearto be far brighter than the others. When we use photo-
`metric quantities, then, we are measuring the properties of visible radiation as they
`appear to the normal eye, rather than as they appear to an “unbiased” detector.
`Sincenot all humaneyesare identical, a standard response has been determined by
`the International Commission on Illumination (CIE) and is reproduced in Figure
`2-7. The relative response or sensation of brightness for the eye is plotted versus
`wavelength, showing that peak sensitivity occurs at the “yellow-green” wavelength
`of 555 nm. Actually the curve shownis the luminous efficiency of the eye for pho-
`topic vision, that is, when adapted for day vision. For lower levels of illumination,
`when adapted for night or scotopic vision, the curve shifts toward the green, peaking
`at 510 nm.Itis interesting to note that humancolorsensation is a function ofillumi-
`
`Sec. 2-3
`
`Photometry
`
`13
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`

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`400
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`450
`
`500
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`550
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`600
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`650
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`700
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`750
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`Figure 2-7 CIE luminousefficiency curve. The luminous flux corresponding to
`1 W of radiant powerat any wavelength is given by the product of 685 Im and the
`luminousefficiency at the same wavelength: ®,(A) = 685V(A) for each watt of ra-
`diant power.
`
`lower levels of illumination. One way to
`nation and is almost totally absent at
`confirm this is to compare the color of stars, as they appearvisually, to their photo-
`graphic images made on colorfilm using a suitable time exposure. Another, very
`dramatic way to demonstrate human color dependenceonillumination is to project a
`35-mm color slide of a scene onto a screen with a low current in the projector bulb.
`Atsufficiently low currents, the scene appears black and white. As the currentis in-
`creased, the full colors in the scene gradually emerge. On the other hand, very in-
`tense radiation may be visible beyond the limits of the CIE curve. Thereflection of
`an intense laser beam of wavelength 694.3 nm fromarubylaseris easily seen. Even
`the infrared radiation around 900 nm from a gallium-arsenide semiconductor laser
`can be seen as a deep red.
`Radiometric quantities are now related to photometric quantities through the
`luminousefficiency curve of Figure 2-7 in the following way: Correspondingto a ra-
`diant flux of 1 W at the peak wavelength of 555 nm, where the luminousefficiency
`is maximum,
`the luminous flux is defined to be 685 lm. Then, for example, at
`A = 610 nm, in the range where the luminousefficiency is 0.5 or 50%, 1 W ofradi-
`ant flux would produce only 0.5 X 685 or 342 lm of luminous flux. The curve
`showsthat again at A = 510 nm, in the blue-green, the brightness has dropped to
`50%.
`
`Photometric units, in terms of their definitions, parallel radiometric units. This
`is amply demonstrated in the summary and comparison provided in Table 2-1. In
`general, analogous units are related by the following equation:
`
`
`
`photometric unit = K(A) X radiometric unit
`
`(2-10)
`
`where K (A) is called the /uminous efficacy. If V(A) is the luminous efficiency, as
`given on the CIE curve, then
`
`14
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`Chap. 2
`
`Production and Measurementof Light
`5/5
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