What are illuminated regions?

Illuminated regions are areas that glow because they’re being lit up by something else.

Imagine you're playing with a flashlight in your bedroom at night. When you turn it on, the parts of the room that the light reaches become bright, those are the illuminated regions. The rest of the room is still dark, but where the light goes, things shine.

Now think about a sunny day outside. The ground under the tree is in the shade, but the part of the playground that’s directly under the sun is bright and warm, that's another illuminated region, lit up by the sun.

Just like your flashlight or the sun, other things can light up areas too. A lamp in a room makes an illuminated region on the floor and walls. Even your phone screen lights up a small part of your face when you're looking at it, that’s a tiny illuminated region!

So whenever something is lit up by a light source, that spot is an illuminated region, just like the parts of the room your flashlight reaches.