How do I make light shine over seams?

I’m making a procedurally generated game with tile-based floors, but spotlights seem to just stop at the edge.

Here is what I’m talking about

I have no idea what I could possibly do about it, and I don’t even know what words I’d use to google this problem.

This can happen when too many pixel lights (that is, real-time point and spot lights) are shining on a single object. Because real-time pixel lights can be very expensive to render, by default, the maximum number of real-time pixel lights that can shine on an object (before additional ones are ignored, as is happening here) are quite limited depending on graphics quality:

  • Fantastic: 4
  • Beautiful: 3
  • Good: 2
  • Simple: 1
  • Fast: 0
  • Fastest: 0

Note that on Fast and Fastest, all real-time pixel lights will be ignored entirely by default. These numbers can be changed in Edit → Project Settings → Quality; naturally, this is the easiest solution: just allow more pixel lights.

However, if at some point the large number of pixel lights causes performance problems, consider baking any lights that don’t have to move around at runtime, or changing large point/spot lights to directional lights, which do not count as pixel lights.