Why do pupils constrict?

Pupils shrink when it’s bright outside so your eyes can see better.

Imagine you’re playing with a flashlight in a dark room. When you turn on the light, it's easy to see everything. But if you suddenly go outside into the sun, it becomes too bright, and you might squint or even close your eyes a little, that’s what happens when pupils get smaller.

Think of your eye as a house, and your pupil is like the front door. When it's dark outside, the door opens wide so more light can come in, you see better. But when it’s bright, like during the day or when you're outside on a sunny afternoon, the door closes a little, that’s why your pupils get smaller.

Your eyes have special helpers called iris (like a colored curtain), and they control how big or small the pupil gets. If there's too much light coming in, the iris tightens up, making the pupil shrink, just like closing a curtain to block some sunlight from entering the room.