Lights Out – Free Logic Puzzle

How to play Lights Out

The board is a grid of lights, some switched on. Tapping a light flips it and the lights directly above, below, left and right of it: on becomes off and off becomes on. Your goal is to turn every light off. It sounds simple, but every press affects up to five lights, so a careless tap can undo your work.

There are 16 levels, starting on a 3×3 board and growing to 7×7. Each level shows a par: the smallest number of presses that solves that board, worked out by the game. Match par for three stars. Finishing a level unlocks the next; New board gives a fresh random layout at the same level and Restart resets the current one.

Every board can be solved

Not every pattern of lights can be switched off on every board size. To avoid impossible boards, each puzzle is created by pressing random squares on a dark board, so a solution always exists. The par value comes from solving the board as a system of equations modulo 2, the method mathematicians use for this puzzle.

Tips and strategy

• Order does not matter. Pressing A then B gives the same result as B then A.
• Never press twice. Pressing the same light twice cancels out, so each light is either pressed once or not at all.
• Chase the lights down. Working from the top row, press the square directly below every lit light. This clears all rows except the last; the pattern left in the bottom row tells you which top-row squares to press before chasing again.
• Use the hint when stuck: it highlights one press from a shortest solution.

History

Lights Out was released as a handheld electronic game by Tiger Electronics in 1995 with a 5×5 grid. The idea of toggling neighbouring cells is older and has been studied in linear algebra, where it is a well-known example of solving equations over two values.

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