© Springer Nature Switzerland AG 2020
R. Shamey, R. G. KuehniPioneers of Color Sciencehttps://doi.org/10.1007/978-3-319-30811-1_58

58. Kohlrausch, Rudolf Hermann Arndt 1884–1969

Renzo Shamey1   and Rolf G. Kuehni1  
(1)
Color Science and Imaging Laboratory, North Carolina State University, Wilson College of Textiles, Raleigh, NC, USA
 
 
Renzo Shamey (Corresponding author)
Email: rshamey@ncsu.edu
 
Rolf G. Kuehni
Email: rolf_kuehni@ncsu.edu
58.1 Helmholtz–Kohlrausch Effect
References
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Portrait © Jürgen Killmann and Universität von Tübingen, 1969

Arnt Kohlrausch was born on October 30, 1884, in Hannover, Germany, a member of an extended family of scientists from the early nineteenth century to the present. His father was professor of electrical technology at the Technical College of Hannover. Arnt Kohlrausch studied medicine at the universities of Marburg, München, and Rostock, graduating in 1911. In 1918, he became lecturer in physiology at the University of Berlin. In 1926, he moved to the University of Greifswald, today in the German province of Mecklenburg. In 1928, he became chair of physiology at the University of Tübingen, where he remained until his retirement in 1951. Kohlrausch was active in several fields of physiology. Perhaps his best-known work is Körperliche und psychische Lebenserscheinungen (Bodily and psychological phenomena of life) [1]. He also did research in visual perception and was one of the founders of the journal Die Farbe (Color). A peculiarity of low-level brightness perception, the Kohlrausch-Knick (bend) is named after him. It refers to a bend in the curve of absolute luminance threshold versus time during dark adaptation, the bend being due to the crossover of absolute thresholds of rods and cones at a certain time after light offset. The perceptual effect to an observer is that a very dim scene suddenly appears brighter as the rod sensitivity rises enough to dominate the visual signal. In English, it is known as the “rod-cone break.” Kohlrausch died on July 13, 1969 [2].

58.1 Helmholtz–Kohlrausch Effect

In 1923, Kohlrausch published an article Über den Helligkeitsvergleich verschiedener Farben, Theoretisches und Praktisches zur heterochromen Photometrie (comparing brightness of different colors, theoretical and practical aspects of heterochromic photometry) [3] in which he investigated in detail the effect of hue on perceived brightness, mentioned earlier by Helmholtz [4]. This was followed in 1935 by the article Zur Photometrie farbiger Lichter (Photometry of colored lights) [5]. As reported by Judd [6], in 1939, J. Urbanek and E. Ferencz introduced the term Helmholtz–Kohlrausch effect for the phenomenon, a term still in use today [7]. Figure 58.1 shows some examples. The six circles have luminance values identical to that of the achromatic surround. To most observers, the circles appear to various degrees, lighter than the gray.
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Fig. 58.1

Examples of the Helmholtz–Kohlrausch effect. All circles have the same colorimetric lightness values as the gray surround

Helmholtz used the term glühend (glowing) to describe the appearance of the chromatic colors compared to the achromatic surround. The strength of the effect varies by hue. Quantitative investigations of the Helmholtz–Kohlrausch effect (HKE) based on the CIE colorimetric system were performed by Wyszecki and Sanders in 1964 [8], the basis of the inclusion of the HKE in the lightness formula of the Optical Society of America Uniform Color Scales [9].