Seeing in the dark
In dim light it is hard for people to see. Many animals are nocturnal, which means they are active at night, and they see far better in the dark than we do. Cats, owls and the tarsier, a small night animal with huge eyes, can hunt when we can see almost nothing. Their large eyes let in more light. Every eye has a pupil, the dark opening in the middle that lets light in. In bright light the pupil gets small to protect the eye. In dim light it gets bigger to let in more light. Our pupils grow bigger too in the dark, and if you wait a few minutes in a dim room, you start to see more. Still, our eyes cannot match a cat’s or an owl’s. These are adaptations, not wishes, and they fit each animal’s way of life.
| Can it see well in very dim light? | Eye size | Result |
|---|---|---|
| person | medium | not very well |
| cat | large for its head | much better |
| owl | very large | much better |
Pupil check. Stand in a bright room (not outside in the sun) and look at your eye in a hand mirror (never use a torch near eyes). The pupil is the black circle. Now go to a dim room and wait three minutes, then look again. Is the pupil bigger or smaller? Draw both eyes in your notebook. Why is a big pupil useful in the dark?