Human Eye

OPTICAL INSTRUMENTS


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LIGHT AND DARK ADAPTATION IN HUMAN EYE


       We have already studied that the amount of light entering the eye through pupil is controlled by iris. But this adjustment takes some time. For example, our eyes cannot see everything clearly when we enter a dark room from a bright light. The reason for this is that in bright light the size of pupil of our eye is small. When we enter the dark room, due to small size of pupil, very little light enters our eyes. But after some time, the pupil expands and we become able to see things as more light enter our eyes now.

Movie Theatre


       In the same way, while coming out from a dark room to bright light, our eyes feel a glaring affect. This is due to the reason that in dark room the pupil is large so when we come out in bright light, a large amount of light enters our eyes and we feel glare. But after sometime, the pupil contracts and we become able to see clearly as less light enters our eyes now.


Test Your Understanding and Answer These Questions:




  1. What is dark and light adaptation?

  2. What happens to our eyes when we enter a dark room from bright sunlight?

  3. What happens to our eyes when we go out suddenly in bright light from a dark room?