I think, that during the sleep, our brain works almost the same as when awake, except it doesn't receive any sense preceptions from organs and creates its own instead. Lucid dreaming is just learning how to improve and control the emulation.

Btw a cool trick for changing the night into a day Close your eyes and pull the sun up on the sky just like opening the garage door or something like that. You should feel that you're actually pulling some weight and your eyelids should ligten up. When you open your eyes, the sun is high in the sky The feeling is really great