Charles Proteus Steinmetz.

Radiation, light and illumination; a series of engineering lectures delivered at Union College by Charles Proteus Steinmetz online

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RADIATION, LIGHT AND ILLUMINATION




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RADIATION. LIGHT AND
ILLUMINATION



A SERIES OF ENGINEERING LECTURES
DELIVERED AT UNION COLLEGE



BV

CHARLES PROTEUS STEINMETZ, A.M., PH.D.



COMPILED AND EDITED BY
JOSEPH LEROY HAYDEN



THIRD EDITION
FIFTH IMPRESSION



McGRAW-HILL BOOK COMPANY, INC.

NEW YORK: 370 SEVENTH AVENUE

LONDON: 6 A 8 BOUVERIE ST., E. C. 4

1918



COPYRIGHT, 1909, 1918, BY THE
McGRAW-HILL BOOK COMPANY, INC.



PBINTED IN THE UNITED STATES OF AMERICA



AUTHOR'S PREFACE.



THE following lectures were given as a course of instruction to
the senior students in electrical engineering at Union University.

They are however intended not merely as a text-book of
illuminating engineering, nor as a text-book on the physics of
light and radiation, but rather as an exposition, to some extent,
from the engineering point of view, of that knowledge of light
and radiation which every educated man should possess, the
engineer as well as the physician or the user of light. For this
purpose they are given in such form as to require no special
knowledge of mathematics or of engineering, but mathematical
formalism has been avoided and the phenomena have been de-
scribed in plain language, with the exception of Lectures X and
XI, which by their nature are somewhat mathematical, and are
intended more particularly for the illuminating engineer, but
which the general reader may safely omit or merely peruse the
text.

The lectures have been revised to date before publication, and
the important results of the work of the National Bureau of
Standards, contained in its recent bulletins, fully utilized.

CHARLES PROTEUS STEINMETZ.

SCHENECTADY, September, 1909.



ill

725190



COMPILER'S PREFACE.



A SERIES of eight experimental lectures on " Light and Radia-
tion" were delivered by Dr. Steinmetz in the winter of 1907-8
before the Brooklyn Polytechnic Institute. Unfortunately no
stenographer was present and no manuscript prepared by the
lecturer. A far more extended course of experimental lectures
was however given by Dr. Steinmetz at Union University in the
winter of 1908-9, on "Radiation, Light, Illumination and Illu-
minating Engineering," and has been compiled and edited in
the following.

Two additional lectures have been added thereto by Dr. Stein-
metz to make the treatment of the subject complete even from
the theoretical side of illuminating engineering: Lecture X on
"Light Flux and Distribution" and Lecture XI on "Light
Intensity and Illumination." These two lectures give the
elements of the mathematical theory of illuminating engineering.

With the exception of the latter two lectures the following
book contains practically no mathematics, but discusses the
subjects in plain and generally understood language.

The subject matter of Lecture XII on "Illumination and
Illuminating Engineering" has been given in a paper before the
Illuminating Engineering Society; the other lectures are new
in their form and, as I believe, to a considerable extent also in
their contents.

In describing the experiments, numerical and dimensional
data on the apparatus have been given, and the illustrations
drawn to scale, as far as possible, so as to make the repetition
of the experiments convenient for the reader or lecturer.

Great thanks are due to the technical staff of the McGraw-Hill
Book Company, which has spared no effort to produce the book
in as perfect a manner as possible.

JOSEPH L. R. HAYDEN.

SCHENECTADY, September, 1909.



CONTENTS.



PAGE

LECTURE I. NATURE AND DIFFERENT FORMS OF RADIATION.

1. Radiation as energy. 1

2. Measurement of the velocity of light. 2

3. Nature of light. 4

4. Difference of wave length with differences of color. Meas-

urement of wave length and of frequency. Iridescence.
The ether. 6

5. Polarization proving light a transversal vibration. Double

refraction. 7

6. The visible octave of radiation. Ultra-red and ultra-violet

radiation. 9

7. The electric waves. 15

8. The spectrum of radiation covering 60 octaves. 16



LECTURE II. RELATION OF Bo OILS TO RADIATION.

9. Electric waves of single frequency, light waves of mixed

frequency. 20

10. Resolving mixed waves into spectrum. Refraction. 21

11. Relation of refractive index to permeability and dielectric

constant. 24

12. Spectrum. 25

13. Continuous spectrum. Line spectrum. Band spectrum.

Combination spectra. 26

14. Reflection, absorption and transmission. 29

15. Conversion of absorbed radiation into heat and light. 30
46. Transmitted light. 31
^7. Opaque colors and transparent colors. 32
v!8. Objective color and subjective color. 33

19. Effect of excess and of deficiency of certain wave length
of the illuminant on the opaque and the transparent
colors. 34

vii



viii CONTENTS.

PAOB

LECTURE III. PHYSIOLOGICAL EFFECTS OF RADIATION.
Visibility.

20. The eye. 37

21. Dependence of sensitivity of the eye on the color. Mechan-

ical equivalent of light. Comparison of intensities of

different colors. 40

22. Sensitivity curves of eye for different intensities. 43

23. Change of shape of sensitivity curve with intensity. 45

24. Harmful effect of excessive radiation power. 48

25. Protective action of eye. 50
. 26. Specific high frequency effect beginning in blue. 51

^ 27. Perception of ultra-violet light. Harmful effects of ultra-
violet. 52
28. Arcs as producers of ultra-violet rays. 55

Pathological and Therapeutic Effects of Radiation.

Power effect and specific high frequency effect. 57

Light as germicide and disinfectant. 59

LECTURE IV. CHEMICAL AND PHYSICAL EFFECTS OF RADIATION.

Chemical Effects.

31. Indirect chemical action by energy of radiation. Direct

chemical action. 63

32. Chemical action of red and yellow rays in supplying the

energy of plant life. Destructive action of high frequency

on plant life. 64

Physical Effects.

A/. 33. Fluorescence and phosphorescence. 66

LECTURE V. TEMPERATURE RADIATION.

34. Production of radiation by heat. 70

35. Increase of intensity and frequency with temperature. 73

36. Efficiency and temperature. 76

37. Carbon incandescent lamp. 78

38. Evaporation below boiling point. Allotropic modifications

of carbon. 81

39. Normal temperature radiation. 84

40. Colored body radiation. 85

41. Measurement of temperatures by radiation. 89

42. Colored radiation and heat luminescence. 90



CONTENTS. ix

PAGE

LECTURE VI. LUMINESCENCE.
Fluorescence and Phorphorescence.

43. Radioluminescence. Electroluminescence. Thermolumi-

nescence. Physical phosphorescence. Chemical phos-
phorescence. Biological phosphorescence. 94

44. Pyroluminescence. Chemical luminescence. 96

45. Electroluminescence of gases and vapors. 98

Disruptive Conduction.

46. Geissler tube and spark. Disruptive voltage. 101

47. Change from spark to Geissler glow. 105

Continuous Conduction.

48. Nature of continuous or arc conduction. 106

49. Distinction between arc and spark discharge. Ill

50. Continuity at negative. 113

51. Rectification of alternating voltages by arcs. 117

52. Efficiency and color. 122

53. Most efficient light producer. 123

54. Electro-conduction from negative, long life, non-consuming

positive, limitation in the available materials. 125

55. Arc most efficient method of light production. 126

LECTURE VII. FLAMES AS ILLUMINANTS.

56. Hydrocarbon flames. 128

57. Effect of rapidity of combustion and of flame shape on

smokiness. 130

58. Effect of oxygen atom in the hydrocarbon molecule on

luminosity. 132

59. Mixture of hydrocarbon with air. 133

60. Chemical luminescence. 134

61. Flames with separate radiator. 135

LECTURE VIII. ARC LAMPS AND ARC LIGHTING.

Volt- Ampere Characteristics of the Arc.

62. Arc length and voltage. 137

63. General equations of the arc. 140
Stability Curves of the Arc.

64. Instability on constant voltage. 142

65. Equations of the vapor arc. 145
Arc Length and Efficiency.

66. Maximum efficiency length of carbon arc. 146

67. Maximum efficiency length of luminous arc. 148



X CONTENTS.

PAGE

LECTURE VIII. ARC LAMPS AND ARC LIGHTING (Continued).
Arc Lamps.

68. The elements of the arc lamp. 151

69. Differential arc lamp. 153

70. Series arc lamp. 157

71. Luminous arc lamp. 160

Arc Circuits.

72. Constant potential and constant current. The mercury

arc rectifier system. The arc machine. 160

73. The constant current transformer. The constant current

reactance. 163

LECTURE IX. MEASUREMENT OF LIGHT AND RADIATION.

74. Measurement of radiation as power. 166

75. Light a physiological quantity. 167

76. Physiological feature involved in all photometric methods. 169

77. Zero method photometers. 170

78. Comparison of lights. 172

79. Flicker photometer. 173

80. The luminometer. 175
* 81. Primary standards of light. 177
* 82. Proposed primary standards. 178

83. Illumination and total flux of light. Incandescent lamp

photometry. 179

84. Arc lamp photometry. 182

85. Discussion. Mean spherical, horizontal, downwards, maxi-

mum, hemispherical candle power. 184

LECTURE X. LIGHT FLUX AND DISTRIBUTION.

86. Light flux, light flux density, light intensity. 186

87. Symmetrical and approximately symmetrical distribution. 187

88. Calculation of light flux from meridian curve of symmetri-

cal radiator. 188

Distribution Curves of Radiation.

89. Calculation of distribution curves. Point or sphere of

uniform brilliancy. 190

90. Straight line or cylindrical radiator. 195

91. Circular line or cylinder. , 197

92. Single loop filament incandescent lamp as illustration. 200



CONTENTS. xi

PAGE

LECTURE X. LIGHT FLUX AND DISTRIBUTION (Continued).

Shadows.

93. Circular shade opposite and symmetrical to circular radia-

tor. 202

94. Calculation of the meridian curves of a circular radiator, for

different sizes of a symmetrical circular shade, and for
different distances of it. 206

95. Circular shade concentric with end of linear radiator. 210

.- Reflection.

96. Irregular reflection. 212

97. Regular reflection. 215

98. Reflector with regular and irregular reflection. 218

^Diffraction, Diffusion and Refraction.

99. Purpose of reducing the brilliancy of the illuminant. 221

100. Effect of the shape of the diffusing globe on the distribu-

tion curve. 223

101. Prismatic refraction and reflection. 224



LECTURE XI. LIGHT INTENSITY AND ILLUMINATION.

Intensity Curves for Uniform Illumination.

102. Calculation of intensity distribution of illuminant for

uniform total, horizontal and vertical illumination. 226

103. Uniform illumination of limited area. 229

Street Illumination by Arcs.

104. Discussion of problem. 234

105. Combined effect of successive lamps. 238

Room Illumination by Incandescent Lamps.

106. Distribution curve of lamp. Calculation of resultant total

intensity of direct light. 242

107. Reflection from walls and ceiling. 246

108. Total directed and diffused illumination. 251

~- Horizontal Table Illumination by Incandescent Lamps.

109. Location of lamps. 253



xii CONTENTS.

PAGUI

^LECTURE XII. ILLUMINATION AND ILLUMINATING ENGINEERING.

110. Physical and physiological considerations. 256

111. Light flux density. Illumination. Brilliancy. 259

112. Physical problems. Ceilings and walls. Reflectors, diffus-

ing globes, diffracting shades, etc. 260

113. Objective illumination. Subjective illumination. Con-

traction of pupil. Intrinsic brilliancy. Direct and in-
direct lighting. 261

114. Fatigue. 263

115. Differences in intensity and in color. Control of color

differences. Shadows and their control. Directed and
diffused light. 265

116. Direction of shadows. 267

117. Color sensitivity in relation to required intensity of illu-

mination. 269

118. Domestic lighting. 270

119. The twofold problem of domestic lighting: daylight and

artificial light. 271

120. Street lighting. 272

121. Defects of present street lighting. 273

122. Tower lighting. 274

LECTURE XIII. PHYSIOLOGICAL PROBLEMS OP ILLUMINATING
ENGINEERING.

123. Physical side of illuminating engineering. Physiological

problems. 277

124. Physiological difference between diffused and directed

light. 278

125. Indefiniteness of diffused light. Shadows cast by diffused

daylight. Equivalent diffusion near light source of
large extent. 279

126. Equivalent diffusion by using several light sources. 281

127. Unequal diffusion in different directions. Complex

shadows. 282

128. Physiological light distribution. 283

129. Physiologically, light not a vector quantity. 284

130. Resultant effect of several light sources. 287



BADIATION, LIGHT, AND
ILLUMINATION



LECTURE I.
NATURE AND DIFFERENT FORMS OF RADIATION.

1. Radiation is a form of energy, and, as such, can be produced
from other forms of energy and converted into other forms of
energy.

The most convenient form of energy for the production of rad-
iation is heat energy, and radiation when destroyed by being
intercepted by an opaque body, usually is converted into heat.
Thus in an incandescent lamp, the heat energy produced by the
electric current in the resistance of the filament, is converted
into radiation. If I hold my hand near the lamp, the radiation
intercepted by the hand is destroyed, that is, converted into heat,
and is felt as such. On the way from the lamp to the hand, how-
ever, the energy is not heat but radiation, and a body which is
transparent to the radiation may be interposed between the
lamp and the hand and remains perfectly cold. The terms
"heat radiation" and "radiant heat," which are occasionally
used, therefore are wrong: the so-called radiant heat is not heat
but radiation energy, and becomes heat only when, intercepted
by an opaque body, it ceases to be radiation ; the same, however,
applies to any radiation. If we do not feel the radiation of a
mercury lamp or that of the moon as heat, while we feel that of a
coal fire, it is merely because the total energy of the latter is very
much greater; a sufficiently sensitive heat-measuring instrument,
as a bolometer, shows the heat produced by the interception of
the rays of the mercury lamp or the rays of the moon.

The most conspicuous form of radiation is light, and, therefore,
it was in connection with this form that the laws of radiation
were first studied.

1



2 RADIATION, LIGHT, AND ILLUMINATION.

2. The first calculations of the velocity of light were made by
astronomers in the middle of the eighteenth century, from the
observations of the eclipses of the moons of Jupiter. A number
of moons revolve around the planet Jupiter, some of them so close
that seen from the earth they pass behind Jupiter and so are
eclipsed* at every revolution. As the orbits of Jupiter's moons
were al cute ted from their observations by the law of gravita-
tion, the' time at -Vhidfi the moon M should disappear from sight,



N
\

\



FIG. 1.

when seen from the earth E, by passing behind Jupiter, 7 (Fig. 1),
could be exactly calculated. It was found, however, that some-
times the moon disappeared earlier, sometimes later than cal-
culated, and the difference between earliest and latest disappear-
ance amounts to about 17 min. It was also found that the
disappearance of the moon behind Jupiter occurred earlier when
the earth was at the same side of the sun as Jupiter, at A, while
the latest disappearance occurred when the earth was on the
opposite side of the sun from Jupiter, at B. Now, in the latter
case, the earth is further distant from Jupiter by the diameter
ASB of the orbit of the earth around the sun S, or by about
195,000,000 miles and the delay of 17 J min. thus must be due to
the time taken by the light to traverse the additional distance
of 195,000,000 miles. Seventeen and one-third min. are 1040
sec. and 195,000,000 miles in 1040 sec. thus gives a velocity of

light of 195>OQ ^ Q( - > or 188,000 miles per sec.

Later, the velocity of light was measured directly in a number
of different ways. For instance, let, in Fig. 2, D be a disk per-
forated with holes at its periphery. A lamp L sends its light
through a hole H in the disk to a mirror M located at a con-
siderable distance, for instance 5 miles ; there the light is reflected



NATURE AND DIFFERENT FORMS OF RADIATION. 3

and the mirror is adjusted so that the reflected beam of light
passes through another hole H v of the disk into the telescope T.
If the disk is turned half the pitch of the holes the light is blotted
out as a tooth stands in front of both the lamp and the telescope.
Again turning the disk half the pitch of the holes in the same



5_MOES




FIG. 2.

direction the light reappears. If the disk is slowly revolved, alter-
nate light and darkness will be observed, but when the speed in-
creases so that more than from 10 to 20 holes pass per second, the
eye is no longer able to distinguish the individual flashes of light
but sees a steady and uniform light; then increasing the speed
still more the light grows fainter and finally entirely disappears.
This means when a hole H is in front of the lamp, a beam of
light passes through the hole. During the time taken by the light
to travel the 10 miles to the mirror and back, the disk D has
moved, and the hole H v which was in front of the telescope
when the light from the lamp passed through the hole H Q , has
moved away, and a tooth is now in front of the telescope and
intercepts the light. Therefore, at the speed at which the light
disappears, the time it takes the disk to move half the pitch of a
hole is equal to the time it takes the light to travel 10 miles.

Increasing still further the velocity of the disk D, the light
appears agiin, and increases in brilliancy, reaching a maximum
at twice the speed at which it had disappeared. Then the light
reflected from the mirror M again passes through the center of
a hole into the telescope, but not through the same hole H i
through which it would have passed with the disk stationary, but
through the next hole H 2 , that is, the disk has moved a distance
equal to the pitch of one hole while the light traveled 10 miles.
Assume, for instance, that the disk D has 200 holes and makes



4 RADIATION, LIGHT, AND ILLUMINATION.

94 rev. per sec. at the moment when the light has again reached
full brilliancy. In this case, 200 X 94 = 18,800 holes pass the
telescope per second, and the time of motion by the pitch of one

hole is OAA sec., and as this is the time required by the light



to travel 10 miles, this gives the velocity of light as 10 -s- -

18,800

or 188,000 miles per sec.

The velocity of light in air, or rather in empty space, thus is
188,000 miles or 3 X 10 10 cm. per sec.

For electrical radiation, the velocity has been measured by
Herz, and found to be the same as the velocity of light, and there
is very good evidence that all radiations travel with the same
velocity through space (except perhaps the rays of radioactive
substances).

3. Regarding the nature of radiation, two theories have been
proposed. Newton suggested that light rays consisted of
extremely minute material particles thrown off by the light-
giving bodies with enormous velocities, that is, a kind of bom-
bardment. This theory has been revived in recent years to ex-
plain the radiations of radium, etc. Euler and others explained
the light as a wave motion. Which of these explanations is
correct can be experimentally decided in the following manner:
Assuming light to be a bombardment of minute particles, if we
combine two rays of light in the same path they must add to
each other, that is, two equal beams of light together give a beam
of twice the amplitude. If, however, we assume light is a wave
motion, then two equal beams of light add to one of twice the
amplitude only in case the waves are in phase, as A l and B l in
Fig. 3 add to C r If, however, the two beams A 2 and B 2 are not
in phase, their resultant C 2 is less than their sum, and if the
two beams A z and B 3 in Fig. 3 happen to be in opposition
(180 degrees apart), that is, one-half wave length out of phase
with each other, their resultant is zero, that is, they blot each
other out.

Assuming now we take a plain glass plate A (Fig. 4) and a
slightly curved plate B, touching each other at (7, and illuminate
them by a beam of uniform light as the yellow light given by
coloring the flame of a bunsen burner with some sodium salt
a part of the light 6, is then reflected from the lower surface of



NATURE AND DIFFERENT FORMS OF RADIATION. 5

the curved glass plate B, a part c, passes out of it, and is reflected
from the upper surface of the plain glass plate A. A beam of




FIG. 3.

reflected light a, thus is a combination of a beam b and a beam c.
The two beams of light which combine to a single one, a, differ
from each other in phase by twice the distance between the two
glass plates. At those points d v d 2 , etc. at which the distance




FIG. 4.



between the two glass plates is i wave length, or j, J, etc., the
two component beams of a would differ by J, f , -, etc. wave
lengths, and thus would blot each other out, producing darkness,



6 RADIATION, LIGHT, AND ILLUMINATION.

while at those points where the distance between the glass plates
is \, 1, Ij, etc. wave lengths, and the two component beams a
thus differ in phase by a full wave or a multiple thereof, they
would add. If, therefore, light is a wave motion, such a structure
would show the contact point C of the plates surrounded by
alternate dark rings, d, and bright rings, y. This is actually the
case, and therefore this phenomenon, called " interference"
proves light to be a wave motion, and has lead to the universal
acceptance of the Eulerian theory.

Measuring the curvature of the plate B, and the diameter
of the dark rings d, the distance between the plates B and A at
the dark rings d, can be calculated and as this distance is one-
quarter wave length, or an odd multiple thereof, the wave
length can be determined therefrom.

The wave length of light can be measured with extremely high
accuracy and has been proposed as the absolute standard of
length, instead of the meter, which was intended to be 10~ 7 of
the quadrant of the earth.

4. It is found, however, that the different colors of light have
different wave lengths; red light has the greatest wave length,
and then in the following order: red, orange, yellow, green, blue,
indigo, violet, the wave length decreases, violet light having the
shortest wave length.

If in experiment (Fig. 4) instead of uniform light (monochro-
matic light), ordinary white light is used, which is a mixture of
all colors, the dark and bright rings of the different colors appear
at different distances from each other, those of the violet near-
est and those of the red the furthest apart, and so superimpose
upon each other, and instead of alternately black and light rings,
colored rings appear, so-called interference rings. Wherever a
thin film of air or anything else of unequal thickness is inter-
posed between two other materials, such interference colors thus
appear. They show, for instance, between sheets of mica, etc.
The colors of soap bubbles are thus produced.

The production of such colors by the interference of rays of
light differing from each other by a fractional wave length is
called iridescence.

Iridescent colors, for instance, are those of mother-of-pearl,
of opal, of many butterflies, etc.

Light, therefore, is a wave motion.



NATURE AND DIFFERENT FORMS OF RADIATION. 1

The frequency of radiation follows from the velocity of light,
and the wave length.

The average wave length of visible radiation, or light, is about
l w = 60 microcentimeters,* that is, 60 X 10~* cm. (or about
? oooo in -) an( l since the speed is 8 = 3 X 10 l cm. the frequency

S
is / = = 500 X 10 12 , or .500 millions of millions of cycles per

LW

second, that is, inconceivably high compared with the frequencies
with which we are familiar in alternating currents.

If, as proven, light is a wave motion, there mast be some thing
which is moving, a medium, and from the nature of the wave
motion, its extremely high velocity, follow the properties of this
medium: it has an extremely high elasticity and extremely low
density, and it must penetrate all substances since no vacuum can
be produced for this medium, because light passes through any
vacuum. Hence it cannot be any known gas, but must be essen-
tially different, and has been called the "ether."

Whether the ether is a form of matter or not depends upon
the definition of matter. If matter is defined as the (hypotheti-



Online LibraryCharles Proteus SteinmetzRadiation, light and illumination; a series of engineering lectures delivered at Union College by Charles Proteus Steinmetz → online text (page 1 of 24)