The foveal light adaptation process

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Abstract
The author''s binocular trichromatic apparatus was improved to determine the sensitivity of the light adapted eye before any appreciable recovery occurred, measured relative to the opposite dark-adapted eye. The use of rotating mirrors and shutters to illuminate, or occlude light from, the eyes obviated the previous delay in observation necessitated by the moving of the observer''s head from adapting to comparison eyepieces; and the now possible fixation of the head by a mouthpiece made possible greater accuracy of comparison. For white adaptations, the sensitivity of the red and green responses was inversely proportional to adaptation intensity, and the recovery curves were linear; the blue response was reduced less than the others, and the recovery curves resembled those given by a mono- or bi-molecular reaction, indicating that the rate of blue recovery may be proportional to the concn. of photochemical substance present. With red adaptations, the red recovery was non-linear, the sensitivity varied as above with the adaptation intensity; the green recovery was linear, and the sensitivity reduced to a lesser extent than the red as adaptation intensity was increased. With green adaptations, the reverse occurred. Yellow adaptations produced some non-linearity in the red and green recovery curves. Differences in the area of the adaptation field had no effect on the sensitivity. All the above results are from tests on the author; but a series of other tests with white adaptations, made with a simpler apparatus, showed about half of those tested to have similar adaptation functions. Interpretation of the results requires the 3 response paths of the Young-Helmholtz theory, but indications of a general luminosity reaction, and of linkages between the blue and yellow, and the red and green responses suggest Hering''s theory. Applications to clinical purposes, and the importance of an "adaptation factor" if the visual efficiency of light sources is to be detd., are discussed.

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