Answer:
When you open yours eyes in a brightly lighted area to a dark room (such as a cinema hall), you experience difficulty in seeing objects for a short while slowly, your vision is improved. This improvement is called dark adaptation. This change is due to (a) regeneration of the visual purple (or rhodopsin), the pigment of the rods, which was earlier broken down due to bright light, and (b) dilation of the pupil permitting more light to enter the eyes.
