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In ocular physiology, adaptation is the ability of the eye to adjust to various levels of darkness and light. == Efficiency == The human eye can function from very dark to very bright levels of light; its sensing capabilities reach across nine orders of magnitude. This means that the brightest and the darkest light signal that the eye can sense are a factor of roughly 1,000,000,000 apart. However, in any given moment of time, the eye can only sense a contrast ratio of one thousand. What enables the wider reach is that the eye adapts its definition of what is black. The eye takes approximately 20–30 minutes to fully adapt from bright sunlight to complete darkness and become ten thousand to one million times more sensitive than at full daylight. In this process, the eye's perception of color changes as well (this is called the Purkinje effect). However, it takes approximately five minutes for the eye to adapt to bright sunlight from darkness. This is due to cones obtaining more sensitivity when first entering the dark for the first five minutes but the rods take over after five or more minutes.〔"Sensory Reception: Human Vision: Structure and Function of the Human Eye" Encyclopædia Britannica, vol. 27, 1987〕 Dark adaptation is far quicker and deeper in young people than the elderly. 〔(Aging and dark adaptation - Jackson GR, Owsley C, McGwin G Jr. )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Adaptation (eye)」の詳細全文を読む スポンサード リンク
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