Light and Dark Adaptation and the Perception of Color*

A description is given of an apparatus which has been constructed for the purpose of investigating, by means of the binocular matching technique, the changes in color perception which arise when the state of adaptation of the eye is altered.The changes in color perception, consequent upon changes in the intensity of the adapting light in seven steps from zero to 100 candles per square foot, have been investigated for two observers. The adapting field size was 60°; the test-field size was 20°.There was found a gradual decrease in the saturation of colors as the adapting light intensity was lowered. At low levels, the saturation increased with increasing test-color intensity; but at high levels, increasing test-color intensity caused most colors to become bluer. The sensation corresponding to dim light seen by the dark-adapted eye was found to be pale blue, and not colorless.A final section considers the problem of how the activity of a fourth “white” receptor mechanism might be reconciled with trichromatic matching, and in particular with the constancy of monocular color matches with changes in adaptation.