why does our pupils shrink we we see light but become big when we see the dark ?

Question: why does our pupils shrink we we see light but become big when we see the dark ?
- Keywords:
  dark,
  light,
  pupil,
  vision
Asked by anon-188380 to Paul, Nadine, Alex on 16 Nov 2018.
- Nadine Mirza answered on 16 Nov 2018:
  
  The shrinking and contracting of our pupils actually controls how much light we allow into our light. When there’s lots of it our pupils go small because there’s so much of it getting in. But when there isn’t any at all our pupils expand to let in whatever light they possibly can!

Question: why does our pupils shrink we we see light but become big when we see the dark ?