A reversed tower defense? Honestly, I don't think I have ever played a game like this. The game itself is simple but I think there are tons of potential to turn this concept into a whole puzzle game. You can make more types of light sources like helicopters that are mobile but have very short range. You can also make more types of ships and boats like a reckless motorboat that rushes forward even in the dark or a cargo ship that may get stuck in the canal if it's not being illuminated constantly while making a turn.