Goal: Turn every light on the board off. Tapping a light flips that light and its neighbors directly above, below, left and right: a lit light turns off, and an unlit light turns on. Lights on an edge or in a corner have fewer neighbors, so only the lights that actually touch them are flipped. Tapping the same spot twice cancels itself out, and the order of your taps does not matter. Plan your taps so that all of the lights are dark at the same time. The puzzle is solved when every light is off.