We address the perpetual grid exploration by a swarm of autonomous, asynchronous, myopic, and luminous robots. We first show that it is impossible for the robots to explore the grid regardless of their number and the number of colors they can take if their visibility range is one. We also show that PGE is impossible with three oblivious robots that have a visibility range of two hops. We then present three optimal algorithms solving the problem. The first algorithm uses four oblivious robots with a visibility range of two, but assumes they agree on a common chirality. For the two other algorithms, no common chirality is assumed. The former uses three robots that have a visibility range of two and a two-color light. The latter uses three oblivious robots under visibility range three.