First of all, make a light object. After that, you would see a layer called lighting where it will darken it. If you are saying that you should go to a lower area to affect the light, it is simple.
In the events, first when you are are on top, make a hitbox so that itbwould hide the layer.
When you go to lower area make another hitbox so that it would show the layer. That way, this is how you could do it. And sometimes, make your object a obstacle forblight. Good luck with that! Time is running out. Be fast! I will check on how you will accomplish soon!
