This is pretty cool, but I think the light world is completely unnecessary from a mechanic point of view. It's basically a tutorial level for the actual game, and right now you have it set up where someone can just completely skip the actual interesting mechanics and just have a really generic experience. Though, I imagine that it was great dev and design practice, so yay for that! You could really throw out the entire light world, though, and the game might be a bit stronger for it.

Also, you have a couple elements in the various rooms that feel a bit cheap. For example, in the light world, you have a series of spikes that pop out of the ground, but the player has no way to see them until they're already up, and there's no way to see the indicator of when they're going to come up. 

In the dark world, bats can camp out right at the area where the rooms change, forcing you to take damage before you've even seen what the room is. Adding some breathing room to some of the more damaging game elements, at least when you first enter the room, would go a long way to feeling a bit more fair.