Circle adjusted to work better but now I think hirdrac was right that it's easier to just calculate a distance from center and use that to determine light levels rather than a whole dpath.

lights.hpp

@@ -10,7 +10,7 @@ namespace lighting {
 
   struct LightSource {
     int strength = 0;  // lower is better
-    int distance = 1;  // higher is farther, in squares
+    float radius = 1.0f;  // higher is farther, in squares
   };
 
   const int MIN = 50;