check out layers. each level would be on its own layer and each light within that level visible only on that layer. or maybe instead you could put invisible light occluders between each level?

yeah here you go

been learning #Godot the past few weeks, and early days but i like it a lot. GDscript feels limited at times but hasn't forced a move to C# yet.
cool things: built-in plugin installs (like unity), everything's a node, free and open-source, multiple renderers, good default keyboard shortcuts

FYI, seems to be an error on your site.