Dr. Corey Leroy
"Roy" Sanders

* National Research Council (NRC) of Canada (1951-1953)
* Ph.D., Imperial College, London

Memories of Roy's NRC friends and colleagues:
Clarence Dodd    Graham Fielder    Alan Robertson    Gary Schofield

Roy was Physicist who worked in the Applied Physics division of the Canadian government's National Research Council (NRC). (See a list of the titles and positions that he held.) He began his career there as on May 18, 1950, and retired in 1979. 

When Roy first began at NRC in 1950 he joined its Photometry and Colorimetry section and worked in its laboratories at 100 Sussex Dr., Ottawa. (See image at right.) 

Between early 1953 and late 1955, he took a leave of absence from NRC to obtain his doctorate in physics in the Department of Technical Optics (Colour) at the University of London's Imperial College in Britain. (See image below.)  While there, Roy continued to receive his NRC salary (although it was reduced by 50%).

Roy's Ph.D. thesis, completed in 1955, was called "The colour rendering properties of illuminants, and their assessment by colour tolerance determinations."  At Roy's memorial service, one of his NRC colleagues, Dr. Alan Robertson, spoke about the novel approach to the physics of "colour rendering" which Roy's thesis promoted.  Roy's early research in this technical field is still being remembered in scientific journals. For instance, his work was discussed in the journal Lighting Research & Technology in a paper called "Memory and preferred colours and the colour rendition of white light sources."

Roy's thesis at Imperial College was completed under the guidance of Dr. W.D.Wright, left, who was a world-renowned physicist in the field of colorimetry. His work forms the basis of the international standard for measuring colour.

While living in London, Roy and Sylvia befriended Professor Wright's other Ph.D. students.  See photo, right, with some of these students, including Nasser (Egypt), Sanders (Canada), Moreland (UK), De (Pakistan), Coug (Spain).  In the front row are Mrs. Moreland, Sylvia (with Heather) and Mrs De.  (Interestingly, Nasser was closely related to Gamal Abdel Nasser who led the overthrow the Egypt's monarchy in 1952 and was that country's president from 1956 to 1970.)

During his NRC career, Roy produced technical reports and published over two dozen papers in leading scientific journals. (See below.)  He led work in NRC's photometry and radiometry lab and was responsible for maintaining and developing Canadian standards for light and radiation. His work applied physics to practical things from fluorescent lights, car signals and the flashing lights on emergency vehicles, to colour TV monitors and standardising the exact shade of red for Canada's flag. (See some 1960s NRC reports mentioning his work.) 

Through his work, Roy also deeply involved with the International Bureau of Weights and Measures (BIPM) and International Commission on Illumination (CIE).  In 1962 he began chairing the BIPM's Working Group on the Primary Standard of Light, a position he held until 1971. In 1963, Roy was also awarded the distinction of being made a Fellow of the Optical Society of America. That was also the year that he began his four-year term as the president of the CIE's Canadian National Committee. Roy remained on this committee until his retirement in 1979 and was its vice president between 1972 and 1975.

Through the CIE, Roy met and worked with scientists from around the world, including physicists from both western and eastern Europe His work at the international level included chairing the CIE's Subcommittee on Spectroradiometry between 1967 and 1971. And, as a leader in the field, Roy was appointed to chair the the CIE's Technical Committee on Photometry and Radiometry from 1971 until his retirement in 1979. In that role, he coordinated the work of international scientists in this field. 

During the 1970s, Roy was in charge of photometric standards and calibrations at NRC.  His work formed an important basis for establishing the relationship between the world’s fundamental units of light (the candela) and power (the watt)Read a short summary of some of this work, which Roy wrote in his late 80s.

Throughout the 1960s and 1970s, Roy's work for NRC took him to high-level scientific conferences in many countries These trips were sometimes combined with holidays with his wife Sylvia and their younger children. Through his connections with scientists in Britain, France, Hungary, Czechoslovakia, Poland, the USSR, Japan, India and South Africa, Roy and Sylvia developed not only working relationships but some long-lasting friendships. These international work-related friendships included leading scientists from East and West.  For instance, American friends, like Luke Thorington (the lead engineer at America's largest light manufacturer, Duro-Test Corp.) visited the Sanders cottage in Quebec in the early 1970s.  On the other side of the Cold War divide, Roy and Sylvia were treated to the hospitality of Soviet physicist Dr. Vera E. Kartachevskaia, who headed the Photometry Lab at the Mendeleev Institute of Métrology. During a work trip there in the late 1960s she had taken Roy and Sylvia on a tour of Leningrad. About 20 years later, they visited her there again.  (Learn more in the subsection called "1985 April 25 - May 18.  'Adventure Peace Tour to the Soviet Union,'" in the "Travels" section.) You can also read more about these friendships in "Mixing Business and Pleasure, Both East and West" and in the "Travel: For Work and Pleasure" section on his "Biography" page. Other details about Roy's many work-related trips can also be found in the "Travels" section. 

Roy's interest in light was diverse.  He was for instance eager that the world move away from fossil fuels and nuclear power to the use of the sun's power.  Roy was ahead of his time in seeing solar radiation as a major potential source of energy which is safe, reliable and sustainable. He became a member of the Solar Energy Society of Canada as early as 1975 and installed an old, now almost antique, solar panel at the Sanders cottage. He was also involved in researching many other impacts of light and helped establishe the CIE's Study Group on the Non-Sensory Effects of Optical Radiation. This involved studying effects as diverse as the ability of solar radiation to kill moulds and bacteria, as well as the role of sunlight in causing cancer.

As part of this work, Roy and fellow NRC scientist David Makow patented an "Ultraviolet Radiation Dosimeter" in 1976. This invention was "a method and apparatus using liquid crystals for indicating and measuring the exposure of objects to radiation especially ultraviolet light radiation." (See NRC photo of Makow, left, in 1958.)

Although Roy retired in 1979 from his position as
a Senior Research Officer at NRC, he did have occasion to keep in touch with some of his closest colleagues.  For example, in 1994 he attended a retirement party for Clarence Dodd who had started work for NRC in 1956 as a technician in the labs run by Roy and two other physicists at NRC.

In 2013, at age 89, Roy was still thinking about physics. At that time he devised a cosmological hypothesis to debunk "Big Bang" theory.  Roy challenged the prevailing scientific narrative by arguing that the belief in a supposed "Big Bang" is caused by false assumptions based on a Doppler-like optical illusion.  This illusion, he argued, was caused by the journey of light through dark matter and dark energy.  Read about his antiBig-Bang ideas here.

Roy's 90th birthday party in 2014, was attended by several of his NRC colleagues and replacements.
In the following year, when the government was celebrating the 50th anniversary of Canada's maple-leaf flag, a ceremony was held at NRC to remember its work in stabilizing and defining the flag's colour. (See photo at left NRC retirees: Ron Burton, Roy and Clarence Dodd.)

At this ceremony, after being honoured for his part in that scientific process, Roy was asked to say a few words.  As Alan Robertson recalled at Roy's Memorial Service:

"After receiving a plaque commemorating the work, Roy was photographed in front of the flag and asked about his feelings. His main comment in response was that he hoped that the flag would never be used to march behind into war."

"In conclusion," Alan said, "Roy was a modest man, an excellent and innovative scientist, an unconventional thinker, and a good friend."

Scientific papers authored and co-authored by
C.L. ("Roy") Sanders (between 1951-1979)

His papers were published in a variety of scientific journals
including Applied Optics, Illuminating Engineering, Metrologia, Motion Imaging (Society of Motion Pictures and TV Engineers), National Bureau of Standards, Optical Society, Planetary and Space Science, Revue d'Optique, and Nature. Some of Roy's pioneering research is still being cited in scientific journals such as Lighting Research & Technology (2015).

The absolute spectral diffuse reflectance of magnesium oxide

By Middleton, W. E.K.; Sanders, C. L.

Journal of the Optical Society of America, ISSN: 0030-3941, Volume: 41, No.6; Publication date: June 6, 1951, Pages: 419–424


The published values of the spectral diffuse reflectance of magnesium oxide indicate that it should reflect more highly in the red than in the blue. Using a modification of the method described by Preston, we have measured the absolute value of this quantity between λ=0.24μ and λ=0.85μ. A very carefully prepared surface of MgO on silver has a reflectance of about 0.98 at λ=0.54μ, where there is a very flat maximum. The reflectance of a fresh surface falls to less than 0.96 at 0.4μ, but exposure to strong ultraviolet light bleaches it, the final result being a reflectance increasing continuously from the near-infrared to about 0.4μ, where it begins to fall sharply, reaching 0.96 at about 0.25μ. A sphere lined with such a bleached surface raises the color-temperature of Planckian radiation a little, and the observed color agrees well with that predicted from the new results. It is believed that these results are reliable to ±0.002 from λ=0.4μ to λ=0.7μ, but different surfaces prepared with equal care may differ in reflectance by at least 0.005.

The bleaching is presumed to be caused by the decomposition of small amounts of magnesium nitride.

The absolute spectral diffuse reflectance of magnesium oxide in the near infrared

By Sanders, C. L.; Middleton, W. E.K.

Journal of the Optical Society of America, ISSN: 0030-3941, Volume: 43, Issue: 254; Publication date: January 1, 1953, Pages: 58

An improved sphere paint

By Middleton, W. E.K.; Sanders, C. L.

Journal of the Illuminating Engineering Society, ISSN: 0019-2333, Volume: 48, Issue: May, Publication date: 1953, Pages: 254–256

First paragraph
In 1950 Miescher and Rometschl reported a very high and uniform reflectance for plates of compressed barium sulphate, either alone or with gelatine as a binder, and suggested its use as a standard of whiteness. In this laboratory we attempted to reproduce their results, following their very clear and detailed instructions with the greatest care, but in several attempts we were unable to obtain nearly as good a white as they claim to have produced, even without the gelatine. Our best result, by an absolute method due to Taylor and confirmed by direct comparison in a recording spectrophotometer, showed the com-pressed BaSO4 to be somewhat yellower than magnesium oxide, its absolute reflectance being measured as 0.963 at
λ = μ, and 0.989 at 0.7μ. It is, of course, possible that our preparation was in some way at fault, but at least it can safely be stated that the use of barium sulphate as a standard white seems too difficult a procedure for ordinary use.

The primary standard of luminous intensity at the National Research Council of Canada [letter]

By Sanders, C. L.; Stevens, B. A.; Middleton, W. E.K.

Journal of the Optical Society of America, ISSN: 0030-3941, Volume: 44, Issue: 88; Publication date: January 1, 1954, Pages: 88–89


Read the letter here.

Le Pouvoir emissif d'un corps noir cylindrique

By Sanders, C. L.; Stevens, B. A.

Revue d'Optique, Volume: 33, Issue: 179, Publication date: 1954

A method given by Gouff
é, to calculate the emissive power of a cavity, cannot be used for a long cylander such as the primary standard for luminous intensity. Yamauti gives a correct result which is 1 – 2 X 10−8 for a cylinder 25 times longer than its radius.

Errata: The Primary Standard of Luminous Intensity at the National Intensity at the National Research Council of Canada

Correlate for lightness in terms of CIE-tristimulus values. Part I

By Sanders, C. L.; Wyszecki, G. W.

Journal of the Optical Society of America, ISSN: 0030-3941, Volume: 47, Issue: May 5, Publication date: 1957, Pages: 398–404 


In order to establish a correlate for lightness in terms of CIE-tristimulus values, a simple experiment was performed using Munsell samples of value 5/. The observers compared each sample with a lightness scale and estimated the value of the neutral which would appear equally light. Analysis of the data by the least-squares method showed that a correlate for lightness may be calculated with good approximation from the tristimulus values by means of a second-degree equation, which, for constant lightness, may be interpreted geometrically as an hyperboloid in the CIE-color space. From this, it is concluded that the CIE method of calculating luminous reflectance and using it as a lightness index does not conform with the visual sensation.

It has been established that although the coefficients of the second-degree equation vary with field size and depend upon the individual observer, characteristic features of the results are maintained in each case.

With respect to color vision theory the nature of the results seems to indicate that the contribution of the violet receptor to the sensation of lightness decreases with field size.

A correlate for lightness in terms of CIE-tristimulus values. Part II

By Wyszecki, G. W.; Sanders, C. L.

Journal of the Optical Society of America, ISSN: 0030-3941, Volume: 47, Publication date: September 9, 1957, Pages: 840–842 

A triangulation technique was used to check the definition of lightness as applied in the previous paper. The results indicate that the procedure of defining lightness in terms of the luminous reflectance of neutral samples is satisfactory.

The investigation has been further extended to show a systematic dependence of lightness index on background color. As might be expected, the lightness index of colors similar to the background is decreased and the lightness index of complementary colors is increased relative to the lightness index obtained using a black background. This effect is due to the change in chromatic adaptation of the eye.

L/Y ratios in terms of CIE-chromaticity coordinates

By Sanders, C. L.; Wyszecki, G. W.

Journal of the Optical Society of America, ISSN: 0030-3941, Volume: 48, Publication date: June 6, 1958, Pages: 389–392 


In previous papers a correlate for lightness (L) was found in terms of CIE-tristimulus values for colors of approximately constant luminous reflectance (Y). L could be expressed by a second degree equation with X, Y, Z as variables. In the present study about 100 samples were selected to cover the gamut of existing surface colors. The lightness-equivalent neutrals were estimated by three observers for these colors under the same conditions as described in a previous paper. The original type of equation could not be used to fit the observational data because of the large differences in luminous reflectance among the samples. However, the L/Y ratios could be expressed by a second degree equation with chromaticity coordinates x, y as variables. This type of equation appears to be valid for all reflecting surface colors.

The assessment of color rendition under an illuminant using color tolerances for natural objects

By Sanders, C.L.

Journal of the
Illuminating Engineering Society, Volume: 54 (10) Publication date: 1959. Pages: 640-646.

Consideration of the color rendering properties of illuminants and of
the methods previously suggested for assessing them indicates the desirability of a more subjective assessment. This paper suggests a proceedure which uses the color tolerance ellipses obtained by subjective judgements of the color rendition of several natural objects.

Color Preferences for Natural Objects

By Sanders, C.L.

Journal of the Illuminating Engineering Society, Volume: 54, Publication date: 1959. Pages: 452-456

First paragraph
Since the advent of artificial sources of light, and in particular the fluorescent lamp, certain difficulties have been experienced in selecting illuminants with energy distributions which make the color of objects appear normal, that is, as they appear in daylight. Although the colors of many objects may be rendered poorly by fluorescent lamps, common natural objects are generally the subjects of complaint. it was thought that these objects might have peculiar spectral reflectance curves or fluorescence which could cause the difficulty. These properties were investigated for tea, butter, the human complexion, potato chips and raw beefsteak, because these objects are known to evoke complaints of bad color rendition.

The Primary Standard of Light

By Sanders, C.L.

Read before the meeting of the  Illuminating Engineering Society on June 12, 1959.

A high-precision photoelectric photometer

By Jones, O. C.; Sanders, C. L.

Journal of the Optical Society of America, ISSN: 0030-3941, Volume: 51, Issue: 105; Publication date: January 1, 1961, Pages: 105–108


During work on the primary standard of light a photometer has been developed which possesses desirable qualities. The detector used is a Gillod-Boutry vacuum photocell with cesium-bismuth cathode surface having a basic sensitivity of 25 μA/lu. The photocurrent is measured by a simple circuit, using balanced electrometer tubes, similar to circuits which have been described frequently over a long period of time in the literature [e.g., C. H. Sharp and H. A. Smith, Trans. IES 23, 434 (1928), and O. C. Jones, R. S. Maddever, and J. H. Sanders, J. Sci. Instr. 36, 24 (1959)] except in one rather important respect which is described fully. The photometer is compact and portable. Battery replacement is only necessary every three months. Differences between successive readings and zeros repeat to ±2/104 when measuring a steady incidence of 10−4 lu. Zero drift is small, necessitating readings only every 15 min. Circuit stability is good, so that the simple balance adjustment need not be used more than twice daily, provided that the triodes are suitably matched. Due to undetermined causes day-to-day variations in sensitivity of 0.5% sometimes occur. 

A photocell linearity tester

By Sanders, C. L.

Applied Optics, ISSN: 0003-6935, Volume: 1, Issue: 207; Publication date: May 3, 1962, Pages: 207–211


Illumination provided by an apparatus with nine pairs of apertures may be used conveniently to test the linearity of photometers. The apertures increase in area from one pair to the next by a factor of two. Thus the range covered is 512 to 1. The apertures are selected individually or in pairs by holes in a rotatable disk. The photometer reading on each illumination level in a pair is determined, and the numerical sum of these is compared with the reading on the two together. The ratio can be used to correct the photometric scale of the receiver. The advantage of this apparatus is the straightforward method of selecting illumination levels, the wide range of illumination, and the easily arranged equipment.

The problem of realizing the primary standard of light

By Sanders, C. L.; Jones, O. C.

Journal of the Optical Society of America, ISSN: 0030-3941, Volume: 52, Issue: 731; Publication date: July 7, 1962, Pages: 731–746


Although the accuracy required of a primary standard of light is of the order of 0.1%, there is a spread of 1% in the size of the candelas derived from the primary standards constructed at several national laboratories. In this paper, the standard has been critically appraised: Some of the suspected weaknesses have been studied experimentally, others are discussed at length.

A tantalum susceptor, used around the crucible containing the platinum to absorb the induced currents and heat the platinum indirectly, increased the photometric precision by an order of magnitude. The technique unfortunately introduced excessive contamination of the platinum.

Since none of the modifications has created the desired improvement in accuracy, other types of light standard may need to be reconsidered. 

Correlate for brightness in terms of CIE Color matching data

By  Sanders, C.L.; Wyszecki, G. W.

International Commission on Illumination (CIE) Proceedings, 15 Session Vienna, Austria, 1963, Paper no. P.63.6

Twenty observers with normal color vision made heterochromatic brightness matches on 96 test colors. A 10° bipartite photometric field with a white surround was used. All test colors and the surround has a luminance of 20 cd/m2. Each observer adjusted the luminance of the achromatic comparison field until it matched the test color in brightness. The luminance (B) of the equally bright achromatic field was compared with the luminance (Y) of the colored test field. Values of log10 (B/Y) generally showed a linear increase with saturation. The data have been used to establish an average observer for heterochromatic luminance matching.

Use of a radioactivated light source for the absolute calibration of two-colour night airglow photometer


An experimental procedure is described for the absolute calibration of a low intensity radioactivated light source against a standard lamp. This light source then could be used periodically to check and calibrate the night airglow photometer which uses two filters to isolate a line emission from the continuum in the night airglow spectrum.

The two filter problem is treated analytically and an expression is derived for calculating the spectral line intensity. Then it is shown that with certain assumptions a simple formula can be evolved and used with the experiment observations obtained with the two colour photometer to obtain the emission rate of photons for a certain wavelength (i.e. in a spectral line).

A versatile spectroradiometer and its applications

By Sanders, C. L.; Gaw, W.

Applied Optics, ISSN: 0003-6935, Volume: 6, Issue: October 10, Publication date: 1967, Pages: 1639–1647


A spectroradiometer is described which is designed to make measurements of spectral radiance, irradiance, transmittance, and reflectance. In one minute the Hilger D300 monochromator is set to the next wavelength to be measured and a measurement is made of (a) the dark current of the photomultiplier, (b) the photocurrent produced by the reference source, (c) a voltage indicating the wavelength, and (d) the photocurrent produced by a test source. An integrating digital voltmeter with a 10-sec gate is used. The data are recorded on punched cards and analyzed by a digital computer. Experimental results are given to illustrate the performance. The applications described include calibration of standards of spectral radiance and irradiance from a blackbody at the freezing point of platinum and the developmet of a color temperature scale.

Thermodynamic considerations in realizing the primary standard of light

By Sanders, C. L.

Metrologia, ISSN: 0026-1394, Volume: 3, Publication date: October 4, 1967, Pages: 119–129

The thermal and spectral radiation characteristics of the cylindrical enclosures used in the primary standard of light are studied in detail. The temperatures at the walls and base of the cylindrical ceramic sight-tubes are calculated on the basis of thermo-dynamic equilibrium. The effect of the spectral emissivity of the ceramic on the apparent spectral emissivity of the base is studied. Changes of about one percent in the luminance of the base can occur with the sight-tubes that have commonly been used. The effect of a temperature gradient in the surrounding ingot is also considered. A practical design is suggested which should permit realization of the primary standard of light with a luminance error, caused by the sight-tube, of not more than 0.1%.

Sanders, C. L.  Gaw, W  Wyszecki, G.

SMPTE Motion Imaging Journal, Volume: 77, Issue: 6, Publication date: June 1968, Page: 622 - 623

The color calibrator permits an observer to compare the color of the peak-white video level on a TV monitor with the standard white provided by filtered light from a lamp in the calibrator. The standard white chromaticity is equal to that from CIE Illuminant D6500. The design, construction, calibration and application of the instrument are discussed. Control of the chromaticity of the peak white from various studios and stations using such an instrument should improve the quality of color television.


Design of glass filter combinations for photometers

By Wright, H.; Sanders, C. L.; Gignac, D. S.

Applied Optics, ISSN: 0003-6935, Volume: 8, Issue: December 12, Publication date: 1969, Pages: 2449–2455


Two nonlinear curve-fitting computer programs have been developed for designing subtractive glass filter combinations for use in photoelectric photometers. One program adjusts the filter thicknesses to minimize the sum of squares of errors at each wavelength and is thus useful in designing a general purpose instrument. The second program minimizes the errors in the photometric measurements of preselected light sources. Filters for correcting various photoelectric detectors to the CIE luminous efficiency function are specified. Several spectral response functions have been utilized including S-4, S-10, S-11, S-20 types, and those of typical silicon diodes, and selenium cells. Practical photometer designs with predicted measurement errors of less than 0.1% are presented.

Photometry: Tasks, problems and organizations

By Sanders, C. L.

Applied Optics, ISSN: 0003-6935, Volume: 10, Issue: December 12, Publication date: 1971, Pages: 2589–2591


This paper discusses some of the tasks and problems of photometry. It describes some of the international and national committees, organizations, and laboratories that carry out these tasks and define and resolve these problems.

The purpose of this editorial is to acquaint nonphotometrists with some of the problems of photometrists and with some of the organizations that are involved in defining and solving these problems. Of course some of these problems go back a very long time as you will find from reading Middleton's' article in this issue. Still I cannot help feeling that if vision had been discovered at the same time as the hologram or the laser, vision would have rightly attracted much more public attention and financial support than either of the others. Therefore, the use of a little space in Applied Optics on the mundane subject of photometry can be justified.

Light may be defined as radiant energy which is capable of stimulating the eye, and photometry is concerned with the measurement of such radiations in respect of their ability to stimulate the eye. Following this definition given by Wright in an excellent extensive treatment of the problem of photometry and knowing the visual phenomena involved, the photometrist must decide which radiometric quantities are important, measure them, and convert them to visual quantities using appropriate factors. If the photometrist must also decide the weighting factors and the acceptable limits of the results, he will need to have knowledge of psychology, statistics, and physiology. Many of the factors for converting radiometric quantities have been accepted by international committees, and it is only necessary that the photometrist know which to use in the case at hand.

The visual phenomena to be considered will include brightness or lightness, glare, resolution or acuity, the functions of photopic, scotopic, and mesopic vision, effect of field size, position, color, movement, duration, shape, observer differences, effect of adjacent and distant sources, additivity (or nonadditivity), and adaptation. Some knowledge is required about the required accuracy and precision of measurement. The extent of observer differences give some indication of required accuracy.

Since radiant energy in the visible region of the spectrum also affects processes other than the human visual mechanism, these radiant quantities may be measured and reported by some scientists for other than photometric use. (In some cases, such as in photographic sensitometry, one finds photometric quantities used because of the absence of more appropriate spectral weighting functions.) These scientists, serving a wider purpose than the production of visual quantities, may be called radiometrists or spectroradiometrists.

Photometric measurements are made at the International Bureau of Weights and Measures (BIPM) in Svres, France, national standards laboratories, commercial standardizing laboratories, industrial laboratories, and universities and by illuminating engineers. The end result of all these measurements is to ensure that in the living environment people are able to see adequately and comfortably.

Read the full text of this paper here

Accuracy of Luminous Flux Measurements of Flourescent Lamps

By Sanders, C. L.; J. Bak; W. Gaw

This article (found in Roy's papers) matches a similarly titled paper by the same three authors which was made at the International Conference on Photometry and Colorimetry. It was organised by the Bulgarian Academy of Sciences and held in Varna, Bulgaria, on 25-30 June 1973. The paper presented at that conference was called:

Corrections of Luminous Flux of Fluorescent Lamps for Sphere Selectivity and Imperfect Receivers.  It was published in the Proceedings of the Conference on Photometry and Colorimetry, Varna, Bulgaria, 1973, pp. 81-86.

First Page
In 1967 we investigated a number of methods of measuring the luminous flux from fluorescent lamps in an integrating sphere using incandescent lamps as standards. The theory behind these methods was given by Bak. The measurements were not reported at that time because it was not possible to achieve the desired reproducibility or the desired agreement between the methods. Since then further measurements indicate the source of some of the problems and it now seems worthwhiIe to report the results and our conclusions.

In the earlier measurements a selenium (barrier layer cell) made by Weston with a Viscor filter was used as the physical photometer. Spectroradiometric measurements on the same lamps were made with the same integrating sphere during separate lightings of the lamps. Four types of 20-W fluorescent lamps were used, i.e., warm white, white, cool white and daylite. The incandescent standard lamp was a flux standard at a colour temperature of 2788 K for all methods. Its spectral distribution was assumed to be Planckian. The methods used were corrected for the spectral transmittance of the sphere and of the sphere window as measured by the NRC spectroradiometer.

Accurate measurements of and corrections for nonlinearities in radiometers

By Sanders, C. L.

Journal of Research of the National Bureau of Standards (NBS). Section A. Physics and Chemistry, ISSN: 0022-4332, Volume: 76A, Issue: 5, Publication date: June 7, 1972, Pages: 437–453

The methods described in the literature for accurately measuring photocell linearity are surveyed and assessed. The effect of not measuring photocell linearity under the conditions used in the final apparatus are considered. Some of the conditions necessary for accurate assessment of the nonlinearity under working conditions are specified. The use of the NRC ″Photocell Linearity Tester″ to measure and correct for the nonlinearity of various receivers is described.

Read the full text of this paper here

The above paper was presented at a conference held at the NBS on March 22-24, 1972, in Gaithersburg, Maryland, USA.  The paper was therefore also published in the proceedings of this conference in a book called Accuracy in spectrophotometry and luminescence measurements, NBS Special Publication 378 NBS Special Publication 378.  His paper appears on pages 63-79.

Required and Achieved Accuracy in Photometry and Radiometry

By Sanders, C. L.

Proceedings of the Conference on Photometry and Colorimetry, Varna, 1973. Pages: 1-12.

This paper was presented to the International Conference on Photometry and Colorimetry organised by the Bulgarian Academy of Sciences and held in Varna, Bulgaria, on 25-30 June 1973.

Accuracy is distinguished from short and long term standard deviation since a small standard deviation may be obtained in measurements containing a large error. A block diagram is given indicating the kinds of quantities to be measured in photometry and radiometry. The quantities include total (and spectral) irradiance, radiance and radiant flux, luminous fluxes luminous intensity and luminance. Lists are given of the methods, auxiliary standards and relationships which are required to compare one kind of quantity to another. Lists are given of the information require about sources, methods, auxiliary standards and relationships if an enlightened choice is to be made regarding the optimum procedures and sources to be used. The accuracy achieved in various intercomparisons is given. Reasons for limited achieved accuracy are suggested. Suggestions are given for improving the accuracy, particularly in measurements outside the national laboratories.

CIE interlaboratory comparison of measurements of photocell spectral sensitivity

By Budde, W.; Sanders, C. L.

Applied Optics, ISSN: 0003-6935, Volume: 12, Publication date: September 9, 1973, Pages: 2099–2107 


The results of an interlaboratory comparison of measurements of relative spectral sensitivity of vacuum photocells are summarized. The comparison was part of the work of the CIE Photometry and Radiometry Committee (TC-1.2). Nine laboratories measured two cells each. The results were corrected for the drifting of relative spectral sensitivity of each cell. The standard deviation of an individual measurement on a cell without filter was less than 2% from 450 nm to 620 nm, increasing to 5% at 390 nm and 690 nm. The standard deviation was larger for a V(lambda) corrected cell, being less than 2% in the range 490-600 nm and increasing to 5% at 475 nm and 660 nm. The largest errors were probably caused by wavelength and bandwidth errors.

Interlaboratory comparison of measurements of the spectral irradiance from fluorescent and incandescent lamps: a report

By Sanders, C. L.; Jerome, C. W.

Applied Optics, ISSN: 0003-6935, Volume: 12, Publication date: September 9, 1973, Pages: 2088–2098


A comparison of spectroradiometric measurements has been completed for the wavelength region from 300 nm to 800 nm. The measurement procedures and results obtained in eighteen laboratories are described. The results are considerably better than those in earlier comparisons. Conclusions regarding procedures to be avoided are given. Without special precautions 45° illumination on the diffuse receiver may cause serious errors. Normal illumination on a plane or a spherical receiver is better. The power in the spectral lines was inaccurately measured by Rossler’s method.

Suggestions sur le partage des responsabilités entre le CCPR, le BIPM et la CIE

By Sanders, C. L.

Afin d'assurer l'accomplissement de toutes les tâches nécessaires et afin de prévenir le chevauchement des programmes de travail du CCPR, du BIPM et de la CIE, on doit préciser le partage des responsabilités. Les suggestions ci-dessous, après discussion , pourraient éventuellement mener  un règle de conduite adoptée mutuellement par le CIE (TC-1.2) et le CCPR et suivie dans l'avenir.

May 1975. Pages: 35-37.  Presented to the
Comité Consultatif de Photométrie et Radiométrie at the BIPM, 8th Session, September 3-5, 1975.

Read it in the preceedings here

Possible comparisons arising from survey of calibration facilities

By Sanders, C. L.

May 1975. Pages: 35-37.  Presented to the Comité Consultatif de Photométrie et Radiométrie at the BIPM, 8th Session, September 3-5, 1975.

Read it in the preceedings here


By Heller, J.W., Low, R.M., Mertz, D.C., Sanders, C.L., Schaefer, A.R., Subotlch, Z.S.

Journal of the Illuminating Engineering Society, Volume: 5, Issue 3, Publication date: April 1976

International directory of calibration services in the field of photometry and radiometry

By Sanders, C. L.

Technical Report,
National Research Council, 1977. 125 pages. Information on 26 laboratories in 16 countries. Published on behalf on the CIE's Technical Committee on Photometry and Radiometry.

The directory was compiled by the Optics Section, Division of Physics, National Research Council of Canada, at the request of the International Commission on Illumination, Technical Committee on Photometry and Radiometry (CIE TC-1.2). It is published as NRC Physics Division Report No. PO-121.

The directory gives information on the calibration services available from 26 laboratories in 16 countries. It is divided into three parts: the calibration of sources, the calibration of receivers or measuring devices and the calibration of reflecting or transmitting materials.

It is hoped that this information will improve the dissemination of photometric and radiometric calibrations throughout the world.

A "Technical Note" describing the directory was published in the journal Metrologia,
Volume: 13, Issue: 55, Publication date: 1977.

Additive colour properties and colour gamut of cholesteric liquid crystals

By Makow, D. M.; Sanders, C. L.

Nature, ISSN: 0028-0836, Volume: 276, Issue: November 2, 5683, Publication date: 1978, Pages: 48–50

Liquid crystals are organic compounds in a state of matter intermediate between the isotropic liquid and crystaline solid. They are fluid but at the same time they exhibit molecular order. Depending on the ordering one distinguishes the smectic, the nematic and the cholesteric liquid crystals (CLC). In the latter, the rod-like molecules are arranged in layers with their long axes parallel to each other. In each successive layer the direction of the long axis is rotated by an angle of 10-20 arc min; the molecules then form a helical structure. The spacing between layers differing by an angle of 360° is called the pitch, p. Due to the periodicity of molecular orientation, reflections from all layers separated by p/2 interfere constructively, if the reflected wavelengths equal the product of the pitch and the refractive indices seen by the wave. This condition is met for a band of wavelength that is relatively narrow and steep and appears as a highly saturated colour. The width of the band equals the product of the pitch and the difference of the two refractive indices of birefringence. Colours produced by such constructive interference, sometimes described as irridescent colours, have also been observed in certain beetles, birds and butterflies4. We report here results of experiments showing that colours of superimposed CLC coatings add like coloured lights and produce a colour gamut greater than that obtained with inks, dyes and pigments.

Photometric and colorimetric measurements on a number of flashing lamp systems for emergency vehicles

By Sanders, C. L.; Gignac, D. S.

Technical Report, National Research Council, February 1979

By C. L. Sanders · G. W. Wyszecki · W. J. Gaw

Article, date unknown

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