Hello! I'm trying to put a sun light inside a cube, but the light stays out of a cube...Why?😅 How can I fix it?
Well, the main thing is, I think, that you are using a Sun Light and that is a light that doesn't have a position, only a direction. It makes no difference, whether you place it inside or outside of the cube. Try switching it to a Point Light for instance...
spikeyxxx Thank you! Another question: Is it possible to put hdri light inside the cube?
korneisgibnev098 Yes, but it's not going to be easy...
Here is an example of lighting Suzanne inside of a cube with an HDRI. 
Now, if you don't want the inside of the cube to be lit by the HDRI, but only the monkey, you will have to use a Mix Shader for the Cube and use an Input > Geometry > Backfacing as the Factor (between Transparant for the outside and anything you want for the inside.).
If you are going to see the outside of the Cube, you'll also have to use a Lightpath Node to make the Camera see the color you want, but make it Transparant for the World (the HDRI).
I warned you it's difficult, but you can do almost anything you want!
spikeyxxx Thank you! It's really difficult, but still possible 😄
spikeyxxx Thank you! It's really difficult, but still possible 😄