I absolutely love the premise of this game, and I think there's really only two things I'd like to point out with it.
Firstly, when Light walks off the left side of the screen, an invisible wall stops them, but there's nothing on the right side. So when Light walks off the right side, they vanish and can't come back.
Secondly, this same mechanic means Shadow can just loop around the screen when Light gets close and always win. There might be a counter I haven't found, but that's what it looks like.
I love the idea, it's a great concept for a game that I wish I thought of myself! I've never seen a game play off of visibility like this, very well done.