If the light dazzles, the diameter of the pupil decreases. In dark viewing conditions, it widens to allow as much light as possible to reach the retina.
Very high light intensities can sometimes cause our receptors to become overstimulated: those affected are blinded and often have to avert their gaze.
Temporal course of adaptation of the eye to dark conditions.
Brightness adaptation, i.e. adaptation to well-lit environments, works within seconds. Dark adaptation on the other hand is a slow process; it can take 30 minutes for the eyes to adapt to dark conditions.