Dark and Light Adaptation: Psychophysics

In the most general sense, dark and light adaptation simply mean getting accustomed to lesser or greater levels of environmental illumination. The importance and efficiency of the mechanisms involved are not obvious subjectively because they function so well. Changes of average luminance by factors of 10, 100, or 1000 occur frequently and pass largely unnoticed; it is only when luminance changes by a much larger factor that we are seriously inconvenienced, either by the temporary blindness resulting from the slowness of regeneration of rhodopsin, or by the unpleasant glare resulting from our inability to reduce our pupil area to the same extent as the domestic cat. Psychophysical measurements show that, though we may not be vividly aware of them, great changes of visual performance nonetheless occur, and the main purpose of this chapter is to describe them.