Why Do Smartphones Automatically Brighten or Dim?

Smartphones use a little sensor called an ambient light sensor to know how bright or dark it is around them. When you walk outside in the sun, the screen gets brighter so you can see better, just like when you turn on a lamp in a dark room. Inside, it dims down so your eyes aren’t tired from looking at a super-bright screen. It’s like having a tiny detective inside your phone that watches how much light there is and changes the screen to match.