Final answer:
The size of the pupil changes to regulate the amount of light entering the eye in different lighting conditions.
Step-by-step explanation:
The diameter of the pupil changes based on the amount of light entering the eye. In normal room light, the pupil will be larger to allow more light to enter the eye.
When the lights are turned off and the room is dark, the pupil will dilate even further to let in as much light as possible. When the lights are turned back on, the pupil will constrict to reduce the amount of light entering the eye.
These changes in the size of the pupil help the eye adjust to different lighting conditions.