PLAYING GUIDE
Every press affects a cross
Pressing a square toggles that light and its horizontal and vertical neighbours. Corners affect three squares, edges usually four, and an interior square five. A light turning on after a move is not necessarily a mistake: the objective concerns the final board.
Two identical presses cancel
Press a square twice and all of its affected lights return to their previous state. The order of presses also does not change which lights are toggled overall. Use these properties to reason about a sequence instead of trying random moves whenever the board looks worse.
Work down the board
After choosing a pattern of presses for the first row, inspect that row. Press directly below any remaining lit square to turn it off. Continue downward. Later presses cannot change a row more than one row above, so this gives a systematic way to test a starting pattern.
When the bottom row will not clear
An uncleared bottom row means that starting pattern did not solve the board. Restart and try a different first-row pattern, rather than undoing the whole method with scattered presses. New boards are made with legal toggles from a solved state, so a solution exists; the fewest-move solution is a separate challenge.
Updated 26 September 2026 · Our editorial method