I didn't really get the concept at first, but once making it to the split path with the (temples?) dark and light areas, the game mechanics clicked!
A lot of stuff felt a bit trial and error until I understood that things functioned like a "power-on and off" state rather than a "swap forms" state. Once I realized that, the game became much more fun. I really like this as a concept, though a few of the platforming challenges felt rough (most notably the fast platforms in the light area where the orb couldn't catch up to the player). This seems like it could be a really good concept given more time and polish!
The art looks very nice. Everything was clear, and I like the little sun and moon man.
Great job overall!