The secure-square problem is this:
Suppose you have a square with mirror edges. In these square, you choose two points, one as a light source and the other as a target. On these square, you can place light-blocking points. The square is called secure, if every ray of light from the source to the target will hit a light-blocking point.
There is a nice solution which states that 16 points are enough to make a square secure.
Can this be extended to triangles, pentagons and other polygons? Are there references on this subject?