The measurement and analysis of colour adaptation phenomena

Abstract

The effects of light adaptation have been measured by first matching a test color, as viewed by the right eye, against a mixture of 3 primaries derived from a trichromatic colorimeter, as viewed by the left eye. The right eye then gazes at a third and more intense patch of light until it is adapted to the higher intensity level, when the test color is viewed again. The effect of the adaptation is measured by re-matching the primaries against the test color and successive matches give the course of recovery of the initial state of adaptation. The left eye thus acts as a standard of reference against which the changes pro-duced by various conditions of adaptation have been measured; for different intensities and color and for varying times of adaptation; and for various wave-lengths and intensities of test color. The analysis of the results shows that there is a main process of adaptation that operates through the regeneration of a photosensitive substance at a constant rate. The instantaneous response aroused by a stimulus is found to be directly proportional to the magnitude of the latter, but owing to the process of adaptation, the response is rapidly reduced to an approximately constant level. This is shown to be the true interpretation of the constancy of the Fechner fraction, as opposed to the suggestion that the response is proportional to the logarithm of the stimulus. By locating the 3 hypothetical stimuli in the color triangle corresponding to those sensations that can be modified in intensity but not in color, no matter what the color of the adaptation may be, it has been possible to determine the fundamental response or excitation curves. The curves obtained do not differ very greatly from Konig''s "fundamental sensation curves." Measurements on the effect of varying the wave-length of adaptation show that there is a specific effect on each response as well as a general depression of sensitivity, and the results indicate the probability that the incident light reacts with one photo-sensitive substance to produce 3 different products, rather than with 3 distinct photo-sensitive substances. Experiments with high intensities of adaptation show that with retinal illuminations above about 15,000 photons, one or more of the visual processes break down and abnormal effects are introduced.