Question

when you enter from a bright sunshine here into a dark room you are not able to see clearly for some time why

Answer 1

Reason:
when you enter from a bright sunshine into a dark room you are not able to see clearly for some time because the focal length of eye lens is completely dependent on the intensity of light .
in first case , when you were in the sunlight ,then the focal length of your eye lens were small in size in order to make you see each and every part.
But in the second case, when you enter in the dark room,then in order to make you see the object present in the room, the focal length has to be large.
therefore , it takes some time to clear the images present in the room.