LIGHT CALCULATIONS AND MEASUREMENTS

Transcription

1 LIGHT CALCULATIONS AND MEASUREMENTS

2 PHILIPS TECHNICAL LIBRARY LIGHT CALCULATIONS AND MEASUREMENTS An introduction to the system of quantities and units in light-technology and to photometry H.A.E. KEITZ SECOND REVISED EDITION MACMILLAN

3 N.V. Philips' Gloeilampenfabrieken, Eindhoven (The Netherlands), 1971 Softcover reprint of the hardcover 2nd edition 1971 All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission. Published by MACMILLAN AND CO LTD London and Basingstoke Associated companies in New York, Toronto, Melbourne, Dublin, Johannesburg and Madras ISBN ISBN (ebook) DOI / PHILIPS Trademarks of N.V. Philips' Gloeilampenfabrieken No representation or warranty is given that the matter treated in this book is free from patent rights; nothing herein should be interpreted as granting, by implication or otherwise, a licence under any patent rights

4 FOREWORD Since the first edition of this book appeared 14 years ago, it has been widely used in lighting practice and as a textbook, and appears to have received an enthusiastic response from users. It was therefore possible to leave the form and content of the book basically unchanged in this second edition. A new section on Dourgnon and Fleury's quasi-central projection has been added to the chapter on the representation of light distributions. A section on the determination of the reflection properties of road surfaces in the chapter on reflection, absorption and transmission has completely been revised. Finally, a new section on the special measures to be taken when measuring the properties of gas-discharge lamps, with or without fittings, appears in the chapter on the measurement of luminous flux. The absorption of colour filters has also been dealt with in somewhat greater detail than in the first edition. Measuring techniques have become much more mechanized and automated of recent years; electronics, and in particular digital techniques, are widely used in this connection. Such methods, which are also widely used for lighting measurements, belong to the field of electronics rather than that of lighting proper. They have therefore not been discussed in detail in this book, which is mainly concerned with basic photometric methods. The author has made grateful use of the remarks and suggestions received from many readers since the appearance of the first edition. The whole text and the illustrations have also been carefully revised, and it is hoped that this second edition will also be of service to its readers in the practical and educational fields. Thanks are due to all who have helped in the production of this book, and in particular to Prof. Dr. H. W. Bodmann of the University of Karlsruhe (until recently attached to the Philips' Lighting Laboratory in Aachen) who read the entire revised second edition through, and to whom many improvements in the text are due. H. A. E. Keitz

5 CONTENTS Page PART I Chapter I I LIGHT CALCULATIONS Introduction The nature of light.... Light as a wave-phenomenon Polarisation Photometry; the photometric system of Lambert The development of lighting engineering Subjects dealt with in this book. I Chapter II Solid Angle Solid angle, steradian... Some special solid angles. Significance of the conception ruinating engineering Small solid angles 5. Table of solid angles "solid angle" in illu Chapter III III-I Chapter IV IV-I. Luminous Flux, Luminous Intensity, Quantity of Light Luminous flux; luminous intensity Units of luminous intensity and luminous flux Formulae giving the relationship between luminous intensity and luminous flux Horizontal, spherical luminous intensity... Luminous efficiency Quantity of light, lumen-second, lumen-hour Light Distribution, Rousseau and Zonal Luminous Flux Diagrams Light distribution, the Rousseau diagram... Construction of the Rousseau diagram.. Derivation of the Rousseau diagram with the aid of the infinitesimal calculus Determination of the efficiency of a lighting fitting from the Rousseau diagram

6 VIII CONTENTS 5. The zonal luminous flux diagram The area enclosed within the luminous intensity curve is not a measure of the luminous flux emitted Average luminous intensity calculated from the Rousseau diagram Russel angles The long-base Rousseau diagram for narrow beams of light Detailed example: determination of a 1000-lm curve for a symmetrical lighting fitting Classification of lighting fittings according to their light distibution 58 Chapter V!If ethods of Representing Light Dt:stribution V-1. Luminous intensity table; polar and rectangular light distribution diagrams 60 The isocandela diagram. 60 Spherical co-ordinates. 62 Sinusoidal projection Transformation of spherical co-ordinates The azimuthal projection Comparison of the sinusoidal and the azimuthal projections Quasi central projection The application of preferred numbers in isocandela diagrams Examples of isocandela diagrams of a fitting...76 Chapter VI VI Chapter VII VII-1. Illumination Illumination; foot-candle; lux The inverse square law... Illumination with oblique incidence. Horizontal and vertical illumination Other units of illumination.,.. Illumination Calculations and Diagrams Introduction The lumen method; coefficient of The point-by-point method... utilization

7 CONTENTS Illumination diagrams The rectangular illumination diagram. 6. The solid of illumination The plane isolux diagram The polar isolux diagram Determination of the luminous flux from the plane isolux diagram The isolux diagram in quasi central projection IX Chapter VIII Luminance and Luminous Emittance VIII-I. Luminance; the stilb, candelas per sq. in Lambert's law The luminous flux of uniform diffusers Luminous flux of a uniformly diffuse cylinder Luminous emittance Emittance and luminance of uniformly diffusing surfaces Units of luminance, based ~m the emittance of uniform diffusers Chapter IX Non-Faint Sources IX-1. Luminous intensity of non-point sources The inverse square law in another form Universal formula for the illumination produced by uniformly diffuse circular light sources Alternative derivations of the formula E = :rcl sin Luminance of light beams Comparison between the illumination values obtained from equations E = Lw and E = :rcl sin Some special applications of the formula E = :rcl sin2 8 = Ija Illumination produced by a uniformly diffuse circular light source in planes parallel to the source Illumination produced by linear light sources Comparison of illumination values of linear light sources as obtained by exact calculation with those obtained by means of the inverse square law Other kinds of non-point source The significance of the foregoing considerations as applied to practical forms of light source

8 X CONTENTS Chapter X X Chapter XI Reflection, Absorption, Transmission Reflection, absorption, transmission.... Regular reflection :.... Reflection factors of non-conductive materials Reflection factor of conductive materials Diffuse reflection Uniform diffuse reflection Luminance factor The luminance factor as a constant of the material 162 Gloss Reflection from road surfaces 168 II. Transmission Density Diffusion factor.. 1 Mvltiple reflection 15. Absorption Absorption of coloured filters 17. Colour of reflected light.. Properties of Optical Systems XI-I. Introduction Relationship between luminance and refractive index; Abbe's law Luminance of images formed by lenses and mirrors, and of the lenses and mirrors themselves Optical systems as light sources; the exit pupil of optical systems Determination of the exit pupil of an optical system; entrance pupil Object at the focus of a lens; angle of divergence The exit pupil of lens systems; vignetting The luminous flux of optical systems. Aperture of lens and mirror systems Some remarks on mirror systems Drum lenses Cylindrical mirrors Facetted mirrors Optical systems for the projection of images Diascopic projection

9 CONTENTS XI 15. Slide projection Standard-film projection Sub-standard film projection The luminous flux emitted by projection systems Episcopic projection Chapter XII XII-I The Photometric Measuring-units System Introduction.... The Luminance criterion... Luminance of coloured light. The relative luminous efficiency The summation law... of radiation Definitions of photometric quantities and units based on v,\ Vision at high and low luminance levels; Purkinje effect Equivalent luminance Minimum perceptible luminance difference and sensitivity to luminance difference PART II Chapter XIII XIII-I. MEASUREMENT OF LIGHT General C on.sider at ions Introduction. Principles of visual and physical photometry Standard light sources Simultaneous and substitution methods. 268 Some practical hints Chapter XIV XIV-I. Visual Photometry and Photometers Principle of the visual photometer Forms of photometer field Methods used in photometers for obtaining the variation of luminance Photometer bench. Some examples of visual photometers

10 XII CONTENTS 5. Homochromatic and heterochromatic photometry Choice of observer Chapter XV XV-I Physical Photometers and Photometry Principles of physical photometers and photometry 295 Photo-emissive cells Photo-voltaic cells Bolometers and thermo-couples 313 Photographic photometry Physical photometers for heterochromatic photometry 315 Chapter XVI Measttrement of Luminous Intensity XVI-I. Principle of luminous intensity measurement. 321 The photometer bench Apparatus for measurement of light distribution 324 Measurements on projectors Photometer with Maxwellian view Chapter XVII Measurement of Luminous Flux, Quantity of Light and Luminous Emittance XVII-I. The Ulbricht sphere photometer Illumination of the sphere window in the "ideal" integrating photometer Illumination of the window of a non-ideal integrating photometer Measures to be taken with non-ideal integrating photometers to approximate to the ideal sphere The measurement of the luminous flux of fluorescent lamps and the appropriate fittings Determination of luminous flu~ from the light distribution or from an isolux diagram Measurement of quantity of light Measurement of luminous emittance. 357 Chapter XVIII XVIII-I. Jfeasttrement of Illumination Introduction Measurement by means of laboratory photometers 360 Visual illumination photometers

11 CONTENTS Physical illumination photometers 5. Calibration of illumination photometers. XIII Chapter XIX AI easurement of Luminance XIX-I. Direct visual measurement of luminance Visual and physical luminance measurements tained from measurement of illumination Measurement of luminance distribution ob- Determination of the size of the exit pupil of lenses 380 Chapter XX ]I,J easurement of Reflection, Transmission and Absorption XX-I. Measurement of reflection factor 381 Measurement of transmission factor. 388 Measurement of absorption Measurement of luminance factors and glos~ 391 APPENDIX International co-operation in Illuminating Engineering 403 Table I Table II - Table of solid angles Values of cos31x cos3 p for a number of values of the angles IX and p Table III - Values of tanp /cos IX for a number of values of the angles IX and P Table IV - Units of illumination and their mutual conversion factors Table V - The units of luminance and their mutual conversion factors Table VI - International relative luminous efficiency of radiation for photopic vision Table VII - International relative luminous efficiency of radiation for scotopic vision Light distribution and zonal luminous flux diagrams for a number oflighting fittings 417 Index 426

12 TABLE OF MOST IMPORTANT SYMBOLS USED IN THE TEXT ex ~ y 8 7J >. 1-' v 7T p a T 'I' 'P w J e E <P 1 b c d I g h i l n r r, R t u v E H I K>. L L M Q s T V>. V>,' alpha beta gamma delta epsilon eta lambda mu nu pi rho sigma tau phi psi omega delta theta s1gma phi Plane angle, absorption factor Plane angle, luminance factor Plane angle Plane angle Emission factor Efficiency of fittings, coefficient of ultilization Wavelength Micro Frequency Reflection factor Diffusion factor, transmissive exponent of diffusing media Transmission factor Plane angle Plane angle Solid angle Small part. of a quantity Half-aperture angle of light beams Sum of a number of quantities Luminous flux Transmissive exponent of transparent media Geographical latitude Velocity of light Distance Focal distance Optical limit distance of photometry, gloss number of Harrison Height Angle of incidence Geometrical longitude, length Refractive index Angle of refraction Radius Time Object distance Image distance Illumination, energy (power) Luminous emittance Luminous intensity Luminous efficiency of radiation at wavelength >. Luminance Equivalent luminance Mechanical equivalent of light, linear magnification Quantity of light Area, density Periodic time International relative luminous efficiency of radiation for photopic vision at wavelength >. International relative luminous efficiency of radiation for scotopic vision at wavelength >.

13 LIGHT CALCULATIONS AND MEASUREMENTS