How to dynamically render a tilemap

I am essentially attempting to render two tilemaps—one base map that is always shown, and a copy of that map that should “override” the base map within a circle.

My initial thought was two have two lighting layers such that each tilemap has their own lighting source, where the base map has a global light so it’s always visible and the override map has a spot light that reveals it dynamically.

The issue with this approach is that surfaces that are not illuminated by a light are rendered black. I essentially want surfaces that are not receiving any light to be transparent instead of black. This would allow the base map to still be displayed when the override map is not lit by the spot light.

If anybody has any thoughts on how to make this possible or any other ways to dynamically reveal a layered tilemap, I’m all ears! Things that could possibly help but that I’m not super familiar with include lighting mixing modes, layering cameras, and shaders. I’m starting to feel like I’ll need to write a custom shader for this… more to learn!

It would seem this person had a similar issue: Sprite is black when no light - Questions & Answers - Unity Discussions

Sounds like a job for a sprite mask, not lighting.

Here’s a thread discussing it https://forum.unity.com/threads/adding-spritemask-to-a-tilemap.989933/