While moving from a dark environment into a very light environment, the visual system experiences a change in sensitivity. Light adaptation involves primarily the cone system, and usually takes less than a minute. These multiple hookups result in very poor visual acuity. However, since each nerve ending serves a relatively large portion of the visual field, the rod system is more likely to detect changes such as motion or flicker. There is no color response with the rod system.
Rods produce a black and white response, which is actually a reaction to variations in luminance.
Moving from a very light environment into a dark environment results in a change in sensitivity of the visual system due to dark adaptation. Dark adaptation is not completely achieved until about 1 hour after light is removed. The initial rapid phase of dark adaptation is due to low-level cone action, while the remaining portion of dark adaptation is due to slower rod action. Scotopic or rod vision occurs when the eye has been dark adapted and only the rods are functioning. When both rods and cones are functioning, the visual system is said to be operating in the mesopic range.