Question

what does happen to pupil of our eyes when we switch the lamp on?

Answer 1

the iris of our eyes is sensitive to brigt and dim light when we switch on the lamp the iris muscles contract and form a lower gap to allow the light into the lens

Answer 2

As we switch the lamp on, the pupil shrinks in order to avoid damage to cornea. As the light entering into the eyes were initially dim but as strong light (from the lamp) entered the eyes, iris changed the size of the pupil, just to protect the cornea. This happens in just few fractions of second but it is very important.