M. Alpern [1]
Stiles attended Burlington (Preparatory) School and St. George’s Higher Grade School. In 1912, he entered the Polytechnic Day School, London, as a student of the Technical Secondary School. In 1918, he won an Andrews Entrance Scholarship (Science) to University College, London and started as a Chemistry student but after one year switched to physics under the influence of Professor Porter. He left University College in 1922 and contemplated whether to continue his higher education in mathematics, medicine, or physics. He decided to study mathematics at St. John’s College, Cambridge. Due to poor health and financial problems, after three terms and having completed no postgraduate research, Stiles left Cambridge and became lecturer in physics and mathematics in the Municipal College, Portsmouth, in the spring of 1923. After a year, he joined the Royal Naval Signal School in Portsmouth as a Junior Scientific Officer. There he developed a sensitive audio-frequency amplifier for electrode signaling. In 1925, he transferred to the National Physical Laboratory (N.P.L.) of Great Britain in Teddington, where he remained until retiring in June of 1961. In his first year, he worked on thermionic emission and on general photometric problems.
Stiles was created OBE (Officer of the British Empire) in 1946 for his wartime work on visibility, visual search, and the defensive use of dazzle. He was elected to the (British) Royal Society in 1957 and was awarded the Tillyer Medal of the Optical Society of America in 1965. He served as General Secretary of the Commission Internationale de l’Éclairage from l928 to 1931, was Chairman of the Color Group of Great Britain from 1949 to 1951, and was President of the (British) Illuminating Engineering Society from 1960 to l961.
73.1 Stiles–Burch Observer
Stiles’ earlier work with B. H. Crawford introduced the concept of veiling glare, a subject of particular importance in street lighting and other applications of illuminating engineering. His name is perhaps best known in the Stiles–Crawford effect, the reduction in sensitivity of the retina as the angle of incidence of the light becomes increasingly different from normal.
In the late 1950s, he spent much time and effort in constructing a visual colorimeter for redetermining the color-matching functions of the average observer. This work, involving measurements on over 50 observers, provided the major basis for what became the CIE 1964 supplementary standard colorimetric observer for field sizes of 10°. The study also included experiments with a two° fields which confirmed the validity of the CIE 1931 standard colorimetric observer, apart from the well-known deficiency in sensitivity at the short-wavelength end of the spectrum. This work also addressed the phenomenon of rod intrusion: the fact that in fields of 10º size, some input from the rods can be added to that of the cones.
Much of his later work was devoted to the study of increment thresholds: the magnitude of the just noticeable amount of a stimulus of one wavelength when superimposed on a uniform field of another wavelength. From these studies, he identified a series of basic visual mechanisms, which he identified as π mechanisms, the significance of which has been a matter for considerable discussion.
Toward the end of his life, he collaborated with Gunter Wyszecki in the writing of Color Science, concepts and methods, quantitative data and formulas, published by Wiley in 1967, with a second edition in 1982. This work still provides an enormous amount of useful data and information on color science.
He was dedicated to traditional psychophysical experimental methods, regarding it as very necessary to avoid arguments founded on introspective descriptions of sensations, which he regarded as notoriously difficult to interpret correctly. He therefore had no contact with the area of magnitude estimation pioneered by S. S. Stevens and further developed subsequently by other workers in color science.
- 1.
G. Wyszeck, W. Stiles, Color Science, Concepts and Methods, Quantitative Data and Formulae, 2nd edn. New York: Wiley (2000).
- 2.
W.S. Stiles, B.H. Crawford, The luminous efficiency of rays entering the eye pupil at different points. Proc. R. Soc. (London) B112, 428–450 (1933)
- 3.
W.S. Stiles, The directional sensitivity of the retina and the spectral sensitivities of the rods and cones. Proc. Roy. Soc. (London) B127, 64 (1939)
- 4.
W.S. Stiles J.M. Burch, Interim report to the Commission Internationale de l’Eclairage, Zurich, 1955, on the national physical laboratory’s investigation of color matching, Optica Acta 2, 168 (1955)