Answer:
Light
Explanation:
When it comes to the amount of light that enters the eyes, we should know that this amount must be within certain limits, thus being constant. The pupil controls light in and out, so it has openings that contract in bright places and dilates in dimly lit places. So this work done by the pupil is called light adaptation. An example of this is when you wake up in the morning and squint at the light as you open your eyes, but in just a few seconds you can open your eyes all the way, even though the room is brightly lit.
