Lightmap looks blotchy. Rings of light.

I’m developing for android and I just started using lightmaps. In this particular scene the walls just use the cube mesh that comes with Unity. I put the lightmap resolution up all the way to 250, but it still looks like this:

As you can see, rings of light are visible. I suspect it might have something to do with texture settings but I can’t be sure.

I found the problem. In the lightmap settings, the textures were set to be compressed. I unchecked this option and that fixed the problem.