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Newton: In the late 1600s, Isaac Newton started a scientific revolution, for example by a new cause-and-effect understanding of planetary motion. Newton worked out his mechanics in one leap, and it is difficult to imagine it being otherwise. His laws of motion assume that friction is extraneous: "...a body in motion tends to remain in motion..." Very well, that almost makes sense, but he needed to take the next step and say "if I suppose frictionless motion and F=ma, what does that explain?" And then "suppose that planets move without friction." And then, "well, what keeps them on track? How about gravity?" To complete the picture, he wrote an algebraic law for gravity. Then, by the way, F=ma looks simple, but a is the second derivative of displacement with respect to time, so he had to invent calculus. He had to make a revolution. He couldn't make one timid advance at a time, really. He had to put all of his bold ideas on the table.
Let us now be bold and try to describe Newton's approach:
Another view is this. The time was ripe
for Newton's ideas, but suppose that he had not appeared
and a group of lesser minds had made his discoveries.
They would still be geniuses, but maybe two
mathematicians and two astronomers, reading each other's
work. They would have had an extended period of
uncertainty and controversy while they shared their
ideas. They would have needed an atmosphere of patience
and tolerance for uncertainty. Today, some scientists
enjoy such a climate, but others
Big bang of engineering: The two centuries after Newton were a time of great progress for science in general and physics in particular. Engineering was systematic, but technologies were narrow. The 1800s were the age of steam. Also in that era, a funny thing happened. Great minds seemed to work harder and harder, and new ideas were formulated in detail by Gauss, Ohm, Faraday, Henry, Helmholtz, Hamilton, Boltzmann, Gibbs, and others. Using physics that was freshly made clear, Charles Proteus Steinmetz developed the concepts and wrote the textbooks of systematic electrical engineering. Then at the turn of the century, it was enough. You could call it the big bang of engineering, or maybe the ragtime singularity. Edison's electric lights (first patented in 1880) gave impetus and electrical engineers were ready to string their wires and electrify the world. With great new textbooks (plus slide rules and graph paper) engineers had the confidence to change the world. With their collection of ideas from the Ragtime Era, engineers could feel well-trained and even arrogant for a good 50 years. Even vacuum-tube amplifiers were mainly an application of 19th century physics. In the 1950s, transistors were a new paradigm but somebody had to wire them up, so traditional engineering remained vital.
While 19th century ideas were a legacy for engineers to study and apply, physicists in the ragtime era were moving on. 1905 was Albert Einstein's Annus Mirabilis, in which he published 4 groundbreaking articles on the photoelectric effect, Brownian motion, special relativity, and mass-energy equivalence. That was the starting bell for a new era in which physics moved beyond the great discoveries of the 19th century.
So?? So engineers had what they needed, neatly packaged. That was all very well. They took their legacy for granted, as people do. But if we stop to think about the legacy, we notice:
Now look for a creative period that
establishes the scientific understanding of lighting.
It has barely started. The traditional attitude is
mainly that light is good.
So, light is good, and there are
different kinds of light. That is very well. Artists
might begin to notice more, how lighting conditions
vary and how light interacts with objects. To
take us toward scientific understanding, we have
little legacy from ancient times, or from Galileo or
Newton, or even Maxwell. To begin to
understand lighting, we require the whole package of
classical physics, from Newton's insight that white
light is (usually) a mixture of all colors, to the
laws of optics, and the methods of radiometry and
photometry, plus some modern understanding of topics
like color mixture. Late innovations to enable
calibrated optical measurements were Grayson's ruling
engine for diffraction gratings, described in a 1917
publication, and work, including by Langley, on
measurement of optical power. (See below.)
Daylight is variable, but on a sunny day it comprises the rays from the sun's disk plus light from the rest of the sky dome. The sun covers only about 10-5 of the sky dome. ["Lighting quality and light source size," Journal of the IES 19(2):142-148 (Summer 1990). Web version.] Before electric lighting, artificial lights were flames: campfires, candles, oil lamps and so forth. At right is an interior view of Charles P. Steinmetz's summer cabin, showing among other things a kerosene lamp. (The cabin is preserved in a museum. The photo was taken by Nicholas J. Worthey in 2004.)
Then in the age of flame lighting, what did Edison invent? An incandescent lamp, with a filament that was relatively bright and compact and had the color of a flame. With present knowledge we can confirm that the filament was an approximate blackbody radiator and indeed had a spectrum similar to that from a flame. Edison probably understood as much--took it for granted.
In short, incandescent lights were a small step away from the world of flames for lighting. In the year 1912, a person could be an illuminating engineer, but he had mainly one source to work with. The engineering had to do with
The true illumination engineering lies in the steps that go beyond electricity and wiring: positioning the lamps and designing lenses, reflectors and the sources themselves. Electricity can power not only carbon arcs and filaments, but other lights which do not mimic flames at all. Before vapor discharge lamps were common, it was understood how strange they could be. US Patent 1025932, granted to C. P. Steinmetz in 1912 explains: "Hence it appears that an arc between electrodes, at least one. of which is formed of mercury, should be an extremely efficient light-giving arrangement, and this is indeed the fact, but the mercury arc is, unfortunately, of an extremely disagreeable color., It gives a discontinuous spectrum containing the Fraunhoefer lines 4047; 4359; 5461; 5769 and 5790, and some fainter intermediate lines. The sodium line, 5890, sometimes appears faintly, but this is probably due to the action of the glass or the presence of some impurity."
A scientific approach would give some thought to idiosyncratic lights, even hypothetical ones, and how they might affect vision of objects. Herbert Ives's passing remark in a 1912 article, discussed at right, calls our attention to a uniquely strange hypothetical light, a white light that comprises just two narrow bands, a blue and a yellow.
Ives's example was hypothetical but not impossible and its strangeness is echoed in 20th century technologies such as high-pressure mercury vapor lights, and even everyday fluorescent lights.
What does not live on is Ives's spirit of inquiry. His example, a kind of ideally bad light, does not speak to the physics of plasma discharges, but to the way the eye has evolved, with highly overlapping sensitivities in the red and green receptors. By the logic of the two-bands example, our vision of red-green object contrasts is uniquely at risk. But discussions of lighting and color seldom deal with these facts.
The two-band light is an extreme example for lighting and color. For the issue of light source size and placement, an extreme example would be that an object is lighted from all sides, as when it is in an integrating sphere. The discussion can then easily move to examples of compact sources (with small area) and the range in between. Other issues would call for other extreme examples.
A scientific approach would explore the cause-and-effect meaning of each issue and its extreme possibilities. In the 20th century, there was a problem that hypothetical sources remained hypothetical. It was not possible, on a reasonable budget, to build an apparatus that allowed an experimenter to manipulate a parameter such as light source spectrum in a systematic way. The exception that proved the rule was Edwin Land's experiments with projectors, cited at right. The experiments stood out in that the experimenter could turn knobs and adjust the lights. It appears that the setups used considerable lab space and some money, but for a lighting experiment (rather than the interesting experiment that was done), even more projectors might be needed. (For readers who are not native speakers of English: "the exception that proves the rule" is an old expression meaning an exception or extreme case that tests a rule.) In principle, Land showed the way to new lighting experiments, but the apparatus was cumbersome and nobody extended his method to other kinds of experiments.
To learn more about the experiments with projectors as light sources, see http://mccannimaging.com/Retinex/Home.html , then visit the topics Color, Retinex, and Color Constancy .
21st century technology, especially LEDs, will give new possibilities for systematic experiments. It will still take some money and electronics skills.
|Since 500 million years ago.||Evolution of creatures with 2
eyes, including our mammalian ancestors:
Illustration developed by Nicholas Worthey. Chimpanzee photo by Thomas Lerch.
Wilhelm von Leibniz
||"Lagrange was one of the
creators of the calculus of variations, deriving the
Euler–Lagrange equations for extrema of functionals. He
also extended the method to take into account possible
constraints, arriving at the method of Lagrange
multipliers. ... In calculus, Lagrange developed a novel
approach to interpolation and Taylor series. He studied
the three-body problem for the Earth, Sun and Moon (1764)
and the movement of Jupiter’s satellites (1766), and in
1772 found the special-case solutions to this problem that
yield what are now known as Lagrangian points. " [Wikipedia,
article on Lagrange.]
||Did famous experiments in
which electricity caused a dead frog's leg to twitch, 1780. In one experiment,
the frog's leg was in contact with dissimilar metals,
which sufficed to make it twitch. That experiment was
subject to interpretation, but led to the invention of
batteries and the concept of a steady electric current as
opposed to static electricity. By shocking body parts into
action, Galvani inspired the fictional Dr. Frankenstein.
||Starting from Galvani's
observations, Volta realized that when it was contacted by
an arc of two dissimilar metals, the frog's leg was
serving two purposes. It was in effect the electrolyte of
a battery and also the detector of electricity. Volta then
experimented with salt water as the electrolyte, and with
various metals, developing primary batteries and the
electrochemical series, 1800.
On 2015 Feb 18, Google published this animation to celebrate Volta's 270th birthday:
||Introduction to Wikipedia
article on Pierre-Simon Laplace:
"Pierre-Simon, marquis de Laplace (//; French: [pjɛʁ simɔ̃ laplas]; 23 March 1749 – 5 March 1827) was a French mathematician and astronomer whose work was pivotal to the development of mathematical astronomy and statistics. He summarized and extended the work of his predecessors in his five-volume Mécanique Céleste (Celestial Mechanics) (1799–1825). This work translated the geometric study of classical mechanics to one based on calculus, opening up a broader range of problems. In statistics, the Bayesian interpretation of probability was developed mainly by Laplace.
Laplace formulated Laplace's equation, and pioneered the Laplace transform which appears in many branches of mathematical physics, a field that he took a leading role in forming. The Laplacian differential operator, widely used in mathematics, is also named after him. He restated and developed the nebular hypothesis of the origin of the solar system and was one of the first scientists to postulate the existence of black holes and the notion of gravitational collapse."
||Gauss is best known as a
mathematician, but wrote "Gauss's Law," a fundamental
equation in electricity that become one of Maxwell's
|Georg Simon Ohm||1789–1854||Published Ohm's law in Georg Simon Ohm, Die galvanische Kette, mathematisch bearbeitet, Berlin, Riemann, 245 pp., 1827 .|
||One summary from Wikipedia: "His demonstrations established that a
changing magnetic field produces an electric field; this
relation was modelled mathematically by James Clerk Maxwell as Faraday's law,
which subsequently became one of the four Maxwell equations, and
which have in turn evolved into the generalization known
today as field
theory. Faraday would later use the principles he
had discovered to construct the electric dynamo,
the ancestor of modern power generators and the electric
In 1839, he completed a series of experiments aimed at investigating the fundamental nature of electricity; "
||"He also discovered mutual inductance
independently of Michael Faraday,
(1791-1867), though Faraday was the first to publish his
on Joseph Henry.]
||Hamilton is remembered in
particular for the Hamiltonian approach to mechanics. The
Hamiltonian formulation can be applied to more complicated
systems, when direct application of F=ma is
not helpful. He invented quaternions. Modern
vector methods are an alternative for many applications,
but quaternions are still used, particularly to calculate
|Hermann von Helmholtz
||"In physiology and psychology, he is known
for his mathematics of the eye, theories of vision, ideas
on the visual perception of space, color vision research,
and on the sensation of tone, perception of sound, and
empiricism. In physics, he is known for his theories on
the conservation of energy, work in electrodynamics,
chemical thermodynamics, and on a mechanical foundation of
thermodynamics." [Wikipedia, Introduction
to article on Helmholtz.]
On the science of the eye and vision, "His main publication, entitled Handbuch der Physiologischen Optik (Handbook of Physiological Optics or Treatise on Physiological Optics), provided empirical theories on depth perception, color vision, and motion perception, and became the fundamental reference work in his field during the second half of the nineteenth century." [Wikipedia, article on Helmholtz, section entitled 'Ophthalmic optics.']
Notice that even Maxwell's mathematical
formulation of electricity and magnetism can be
construed as an elaboration of earlier work by Faraday
and others. The modern presentation of Maxwell's
Equations as a set of 4 formulas in alternate
forms is itself an extension of Maxwell's original
||Hering is famous for his
opponent-color theory of color vision, which he proposed
[Wikipedia, introduction to article
on Ewald Hering].
Many sources (such as Wikipedia) may emphasize the dispute between Hering's opponent color theory and that of Thomas Young, James Clerk Maxwell, and Hermann von Helmholtz, who emphasized 3 primary colors, red, green and blue. The Wikipedia article on Hering says "But nowadays we know that if the human possesses indeed 3 types of receptors as proposed by Young, Maxwell and Helmholtz they are then combined in 3 opponent channels as proposed by Hering. In their way both Hering and Helmholtz were right."
Wikipedia is correct that both Hering and Helmholtz were right. In this case, I (James Worthey) suggest that opponent colors is a bedrock idea that fits various kinds of evidence:
||Langley is famous for his
aviation developments before the Wright brothers's first
manned flight. He invented the bolometer, "an instrument
for measuring infrared radiation," according to Wikipedia.
His 1881 paper, The Bolometer and Radiant Energy, became
a scientific classic. [Wikipedia article
on Samuel Pierpont Langley.] Although I am frankly
not finding more detail right now, I believe that
Langley's work was pivotal in that he measured light by
its heating effect, leading to related methods with "flat
spectral response," as we would now say. Such objective
measurements of radiation in the visible wavelength range
were a prerequisite for measurements on humans leading to
the 1924 Vλ
function and the 1931 color-matching functions.
|Thomas Alva Edison
||Filed for his first electric
light patent in 1879 and it was granted in 1880, U.S.
patent 223,898 ,
|Charles Proteus Steinmetz
||Steinmetz was a mathematician
and engineer. He held over 200 patents and studied
lightning. But he also stands out as the man who literally
wrote the book for 20th-century electrical
equations are powerful but abstract. Ohm's law is
simple, V=IR , but if V is
time-varying, it does not apply to capacitors and
inductors. Engineers often work with special cases in
which V and I vary as sine waves.
Steinmetz called on his mathematical training to simplify
the algebra needed for such "AC circuits." He was a
pivotal figure, establishing the terminology and methods
so that electrical engineers can design systems and
communicate with each other. Many of Steinmetz's writings
can be found through archive.org and Google Books,
and Calculation of Alternating Current Phenomena
Looking at Steinmetz's contributions to AC circuit theory, we can say that the ideas were inevitable. For example, consider a capacitor (called a condenser in Steinmetz's day I believe) as an element in a circuit. Physics teaches that the current is proportional to the time derivative of voltage, I = C dV/dt . If applied voltage is a sinusoid, then you may write something like V = V0 sin(2πft) and I = 2πfCV0 cos(2πft) and so forth. The current is out of phase from the voltage. The current through a resistor is in phase with the voltage, and then if you add those currents you are adding a sine and a cosine with different amplitudes and some kind of trigonometric identity comes into play. An engineer would notice that he is doing much tedious algebra with great similarities from one problem to the next. Steinmetz realized that the repetitive steps could be written more easily and compactly using complex numbers. In effect, sine and cosine waves add as perpendicular vectors, while differentiation reduces to complex multiplication, and so forth. Because he worked quickly and wrote actual textbooks, his ideas must have gone in a short time from being unexpected and odd to being the iron-clad rules of self-confident engineers. History tends to celebrate tangible gadgets and not the books that the inventor read or wrote. However, it does appear that Steinmetz showed up at the right moment and was a smashing success as a textbook author, among his other accomplishments.
Steinmetz's writings covered DC and AC machines and more. I emphasize AC circuit theory to show how 20th century engineering came to be. By 1900, physics reached a plateau of completeness, a basis for design and analysis of practical machinery. Then a transition was needed, to take from physics a subset of ideas that can be applied again and again to analyze practical systems. In the electrical realm, Charles Proteus Steinmetz personified that transition and what it means to create a body of practical methods based on valid science.
||British-born Australian who
made fine ruling engines for the production of diffraction
gratings. While a prism can separate the colors of the
spectrum, diffraction by a grating establishes wavelength
in absolute distance units. Grayson developed a ruling
engine for gratings. "In 1913 he
was working full time on the grating project... . Grayson
wrote an article on the engine in the Proceedings
of the Royal Society of Victoria (1917)
and was awarded the David
Syme research prize in 1918." [Australian Dictionary
of Biography, article
on Grayson by H. C. Bolton]
||Ives invented a method for
full-color photographs that was "commercially
available in England by late 1897 and in the US about a
year later." [ Wikipedia
article on F E Ives] The method was based explicitly
on the trichromatic theory of color, as he explained:
These writings are available by searching
on the web, or by contacting James Worthey.
That statement, and the detailed
explanation that goes along with it, lays out an idea
that now can be called "The Maxwell-Ives Criterion."
Today we see have the concepts of block diagrams and
linear algebra, so a modern statement is Michael Brill's
termed Einstein's Annus Mirabilis, he published 4
groundbreaking papers on
his father Frederic Eugene Ives, Herbert was an expert on
color photography. In 1924, he transmitted and
reconstructed the first color facsimile, using color
separations." He was
president of the Optical Society of America in 1924-25. [
article on H E Ives ] Of particular interest
for this chronology of quantitative color is Herbert
Ives's role in the development of the 1924 Luminosity
Function, and an observation that he made about lighting
and color. See the next item, concerning one volume of a
journal about lighting.
of the Illuminating Engineering Society, Vol. 7.
Transactions of the IES, Volume 7, is available on Archive.org as one big file. Click the link above to download it. You will have 3 articles by Herbert E. Ives and other writings which reveal how lighting was understood, or not, 100+ years ago.
||Transactions of the
Illuminating Engineering Society, Volume 7,
from the year 1912,
contains 3 articles by Herbert E. Ives. Of particular
The first article is on the topic that we
might call "lighting and color," or "color rendering,"
although Ives's title is clear in itself. In that
article he observed "It is, for instance, easily possible
to make a subjective white, as by a mixture of
monochromatic yellow and blue light. A white surface
under this would look as it does under "daylight" but
hardly a single other color would." Although Ives does not
explain at length, he supplies a graph. We can assume
that the monochromatic blue is at about 450 nm, and the yellow
is at about 580. See below, near
the end of this timeline, how Thornton and Chen in 1978 revived Herbert
Ives's 1912 idea of
a white light that comprises a blue narrow band plus a
yellow narrow band. Worthey drew the connection of the
Thornton and Chen work to that of Ives. [James A. Worthey,
"Limitations of color constancy," J. Opt. Soc. Am. A
2, 1014-1026 (1985). ]
Red, yellow and green hues will not be distinguished if the light contains narrow-band yellow, but no red and no green. Herbert Ives was pointing out, in 1912, the issue that leads to "color rendering" problems, however you want to say it. And where did he publish this insight? In the Transactions of the Illuminating Engineering Society, the predecessor publication to the Journal of the IESNA, still put out by the same society. Of course the famous color-rendering document was first published by the CIE (Commission Internationale de L'Eclairage) in 1965. Did they acknowledge Ives's insight? No, not then and not now. Thornton and Chen called attention to the issue in 1978 (citation below). Worthey first used opponent colors as an approach to the same issue in 1982 (citation below). Opponent-colors thinking led to Vectorial Color. (Citations below.)
Vectorial Color is the answer to more than one problem, but look at the figure above, where narrow bands at 450 and 580 nanometers were laid into Ives's drawing. 580 is indeed yellow. Also in the drawing it is roughly the wavelength where the red and green sensitivities cross. That emphasizes that it stimulates both systems, so it "makes sense." But the point where those functions cross depends on the scale of the functions, so it's arbitrary. In his work under the heading of "Matrix R," Jozef Cohen revealed a deeper truth about color mixing that does not depend on the way the sensitivities are scaled, or added and subtracted. Vectorial color combines Cohen's insights with the opponent-color formulation.
At left are the red, green, and blue receptor sensitivities based on the CIE 1931 observer. We can imagine a 2-bands light drawn in here, again at 450 and 580 nm.
At left is a self-explanatory figure based on the (x, y) diagram and a 2-bands light slightly different from the one above.
Notice that lightmeter sensitivity, the y-bar function graphed below, is near its peak at yellow wavelengths of 570 to 580. So Ives's example is one that cheats on an illuminance requirement. It stimulates the lightmeter but deprives the user of red-green contrasts. Ives did not give a practical example, but fluorescent lamps (introduced about 1939) do this exact thing, presenting a 2-band spectrum, but with a broad yellow band so that red-green contrasts are not totally eliminated.
So that's color rendering. Traditional 4-foot or 8-foot fluorescent tubes have another failing. That is, the surface luminance is much lower than the luminance of a tungsten filament. The lower luminance source has a greater area, causing loss of shading, shadows and highlights, and converting the highlights to veiling reflections. Traditional fluorescent lights do everything wrong at once.
|Transactions of the Illuminating Engineering Society, Vol. 7.||1912||In the same volume of Trans.
Illum. Eng. Soc., the second Ives article deserves a
"Heterochromatic photometry, and the primary standard of light," pp. 376-387.
||2-degree observer data
published, along with the XYZ system for color algebra. 1931
introduced. Sources differ on the date, but they went
commercial in about 1939.
||Claude E. Shannon, "A
Mathematical Theory of Communication," Bell System
Technical Journal, Vol. 27, pp. 379–423, 623–656, 1948. Scans of the
original articles are available:
However, an updated and reformatted
version is linked at: http://cm.bell-labs.com/cm/ms/what/shannonday/paper.html
James Gleick's book The Information,
cited below, puts information theory in context and
explains its importance. Imaging, lighting, and vision
itself are about the transmission of information.
Contrasts are the stimulus to vision.
||The National Television
System Committee was first established by the United
States Federal Communications Commission in 1940 to
establish a standard for analog black-and-white
television. The committee was reconstituted in 1950 to
standardize color television. [Wikipedia, article
on NTSC.] As a standards committee, the NTSC was not
necessarily a creative or scientific body. But the 1953
NTSC standard was based on analytical ideas about vision
and color. It was a point of reference for applied color
discussions and what works--what actually fools the eye. A
textbook discussion of the fundamental color matching
experiments may seem abstract and complicated. But every
pixel of a TV picture is an example of additive color
mixing. (Analog TV had bandwidth limitations, but not
pixels as such.)
|Hans E. J. Neugebauer
||H. E. J. Neugebauer, “Quality
Factor for Filters Whose Spectral Transmittances are
Different from Color Mixture Curves, and Its Application
to Color Photography,” J. Opt. Soc. Am. 46(10):821-824
Application of the Maxwell-Ives principle.
|Michael J. Crowe
||Michael J. Crowe, A
History of Vector Analysis (Notre Dame, Indiana:
University of Notre Dame Press, 1967);
(New York: Dover, 1994). Vectors are a freshman topic and
we take vector algebra for granted. But if you stop to
think, the modern understanding is complicated:
Crowe's book reveals the struggles
leading to this intricate schema. See a
|Jozef B. Cohen
|William A. Thornton
In the 4th item, “What
is visual clarity?” Thornton and Chen revive Herbert
Ives's suggestion (above) that a specified white can be
matched by a mixture of 2 narrow bands. Their Fig. 1:
are a set of standards developed by the Advanced
Television Systems Committee for digital television
transmission over terrestrial, cable, and satellite
networks. The ATSC standards were developed in the early
1990s by the Grand Alliance, a
consortium of electronics and telecommunications companies
that assembled to develop a specification for what is now
known as HDTV. ATSC formats
also include standard-definition
formats, although initially only HDTV services were launched
in the digital format. " [Wikipedia
See the discussion above on the 1953 NTSC standard. The newer standards for high-definition TV are another reference point for thinking about analytical methods and what works for humans. Television standards are about delivering visual stimuli to users. "High Definition" implies high black-white and color contrasts (as appropriate to the original scene) with sharp edges.
Lighting systems control black-white and color contrasts that potentially exist in a scene. Lighting that pleases users will imbue a scene with the same virtues that are valued in high-definition video. In a way that is obvious and has been understood for decades. However
| George E. Smith
||George E. Smith, “The vis
viva dispute: A controversy at the dawn of
dynamics,” Physics Today, October 2006, pp. 31-36. In
freshman physics, we learn that kinetic energy = E
= ½mv2 and momentum
= p = mv. Both measures are conserved, but
the conservation laws obviously differ in their details.
Great minds struggled over which was the true measure of
motion, mv or mv2
< The vis viva dispute is one topic in the pictorial timeline at the top of this page. >
||"Opponent-colors approach to color rendering,"
J. Opt. Soc. Am. 72(1):74-82 (1982).
A. Worthey, "Vectorial color," Color Research and Application, 37(6):394-409
A. Worthey, "Applications of vectorial color," Color Research and
Application, 37(6):410-423 (December 2012).
|Michael H. Brill
Michael took responsibility for the final
editing of Jozef B. Cohen's book, Visual Color and
Color Mixture, published posthumously. See above.
|James Gleick||1954-||James Gleick, The Information: A History, a Theory, a Flood. New York: Pantheon Books, 2011.|
||Sean F Johnston, A
History of Light and Colour Measurement, Bristol:
Institute of Physics Publishing, 292 pages, 2001.
Johnston notes (at length) the peculiar beginnings of the profession of Illumination Engineering. The initial challenge was to quantify light. In the preface, p. ix: "The measurement of brightness came to be invested with several purposes. It gained sporadic attention through the 18th century. Adopted alternately by astronomers and for the utilitarian needs of the gas lighting industry from the second half of the 19th century, it was appropriated by the nascent electric lighting industry to ‘prove’ the superiority of their technology. By the turn of the century the illuminating engineering movement was becoming an organized, if eclectic, community promoting research into the measurement of light intensity."
|James K. Bowmaker
||James K. Bowmaker, "Evolution
of vertebrate visual pigments," Vision Research 48(20):2022-2014,
September 2008. This
review article is one reference for the pictorial on the
evolution of the visual system, specifically the claim
that trichromatic vision in simians evolved 35 million
years ago. Many mammals have dichromatic vision, and a few
are trichromatic, as Bowmaker explains in detail.
We found Bowmaker's interesting article free of charge: http://www.sciencedirect.com/science/article/pii/S004269890800148X . Our search began with the powerful PubMed online index: http://www.ncbi.nlm.nih.gov/pubmed . PubMed indexes materials that are free and ones that are not free, but many interesting items are free.
There is a free textbook called Webvision that is hosted by National Library of Medicine and also by University of Utah:
http://www.ncbi.nlm.nih.gov/books/NBK11530/ or http://webvision.med.utah.edu/ .
In Webvision, the emphasis is on anatomy, but some other topics are included.