Image from Brian Crawford obituary, written by D. A. Palmer, published in the newsletter of The Colour Group (Great Britain), Volume 17, Number 1, February 1992
Brian Hewson Crawford was a British physicist who made important contributions to the science of vision, colorimetry, lighting, and color rendering. He was born on March 26, 1906, in Hornsey, London, to Andrew Crawford and Marian Hewson (Fairweather) Crawford. He was married to Margarethe Bettina “Marga” Nagel, who was a native German from Darmstadt. He died on May 5, 1991, in London, England.
Crawford went to University College London, graduating with first-class honors in physics at the age of 19. After a brief spell at the Rodenside Laboratory of the photographic company, Ilford, he joined the staff of the National Physical Laboratory (NPL) in 1927.
He continued to work in the conservation department of the National Gallery long after officially retiring from NPL. He also made investigations on color in the laboratories of the University of Edinburgh, the Paint Research Association, Imperial College, and the Institute of Ophthalmology. He went on publishing original papers until the age of 79, thus refuting the idea that scientific research is only for young people.
Crawford’s interests were very wide and included languages, painting, and music. His attitude to life was well illustrated by his remark after breaking his wrist in a fall from a bicycle that it had reset at a more convenient angle for playing the viola. While not one to hanker after honors, he was proud of his Doctorate of Science from the University of London and his Newton Medal from the Colour Group (Great Britain), of which he was a past Chairman and Honorary Member.
76.1 Crawford–Stiles Effect and Other Contributions
Joining the NPL in 1927 resulted in a most fruitful association with Walter Stanley Stiles, under the beneficent aegis of John Walsh. A brilliant series of papers followed in the Proceedings of the Royal Society, on such new topics as equivalent backgrounds, increment thresholds, and above all, in 1933, the directional sensitivity of the retina to light and color. These Stiles–Crawford effects [1] comprise the reduction of brightness (the first kind) and the change of hue and saturation (the second kind) of stimuli entering the periphery of the iris compared to stimuli entering the center of the iris. These effects were discovered during attempts to build a visual photometer based on pupillometry. The then “usual assumption that the apparent brightness of an object is proportional to the pupil area” was soon demolished.
Such serendipity was characteristic of both scientists, but important discoveries fall only to those who deserve them. Crawford would say that you only had to search about in any field and you were bound to find out something interesting. No doubt, this was so in his case. His 1947 Proc. Roy. Soc. paper on “Visual Adaptation in Relation to Brief Conditioning Stimuli” [2] is not obviously inspired by temporary blinding effects of gunfire flashes during the Second World War, but that was how “Crawford Masking” was discovered. This is the effect whereby a bright stimulus can be perceived prior to a later less bright stimulus.
It is interesting to compare and contrast the large-field colorimeters, which Stiles and Crawford had each constructed in adjacent laboratories. Stiles’ machine was workshop-built to the highest NPL precision and endowed with such facilities as a meteorology station of hygrometers, barometers, and thermometers, to monitor changes in the refractive index of the air. Crawford’s apparatus belonged to the string and sealing wax tradition, with corks for nonslip knobs and strips of graph paper for scales. Both instruments served their respective purposes admirably.
Perhaps, one explanation of the successful early partnership and later divergence was a creative tension between opposite natures. To draw an analogy from art, Stiles’ science was classic; like Nicolas Poussin, he had neglected nothing. Crawford was romantic; he was fond of quoting Maxwell’s dictum that it is always worth playing a trombone to a petunia at least once, you never know what might happen. But Crawford could work to the highest NPL precision and accuracy when required, as he did in determining the average scotopic spectral response of the human eye, by recording scotopic brightness matching; this led to the international standard for spectral luminous efficiency for scotopic vision (the V’(λ) function), which forms the basis of the present CIE definition. Not least was the difficulty of eliminating the effects of minute amounts of stray light and simultaneously discrediting data produced by several investigators who had not been so careful.
He also showed that color-matching functions made when matching monochromatic stimuli were different from those made when matching white stimuli. An explanation of this phenomenon is still awaited.
Crawford’s last years at NPL were occupied with a study of the color rendering properties of artificial light sources, and he made a great breakthrough in convincing suspicious experts in art galleries and hospitals that certain fluorescent lamps were suitable for their exacting requirements. Typical of Crawford was his finding that combinations of tungsten filament lamps and “Radar Blue” fluorescent lamps could imitate almost perfectly any phase of natural daylight. The resultant equipment was essential in providing a transportable reference illuminant for the darker corners of the Victoria and Albert Museum and the Sheffield Royal Infirmary.
With the kind permission of the Colour Group (Great Britain), this account is based largely on the obituary written by Dr. D. A. Palmer and published in its newsletter, Volume 17, Number 1, February 1992.