Why does it take sometimes to see objects in a cinema hall when we just enter the hall from bright sunlight?

Why does it take sometimes to see objects in a cinema hall when we just enter the hall from bright sunlight? Explain in brief.

The pupil regulates and controls the amount of light entering the eye. In bright sunlight, the size of the pupil is small and when we enter the cinema hall it takes sometime for the pupil to expand in size due to dim light.