The eye needs to respond to different light intensities in a wide range over seven orders of magnitudes. In addition to the adjustment of the pupil, this wide range of intensities is also accomendated by two different types of receptors, the rods for night (dark, scotopic) vision and the cones for daylight (bright, photopic) vision, and the adaptations of the cones.
Dark adaptation: The transition from all-cone photopic vision to all-rod scotopic vision which takes about 20-25 minutes.
Light adaptation: The transition from all-rod scotopic vision to all-cone photopic vision which takes about 5-10 minutes.
The cones can further adapt to several orders of magnitudes of light intensity.
