Journal of Statistical Physics, Vol. 90, Nos. 1/2, 1998. p. 453-466.
The technique of unfolding a polygonal billiard table is used to answer certain questions concerning the illumination problem. The main problem addressed is how many point obstacles would suffice to block any billiard path between two points of the polygon. The answer can then be generalized from point obstacles to small e-neighborhoods of points.