How to play Light Switch
Each press flips a square and its neighbours — find the presses that switch every light off. Also known as Switch-off-the-lights puzzle, Flip grid.
The rules
- The board is a grid of lights, some on and some off.
- Pressing a square flips it and its neighbours: above, below, left and right (or all eight around it, on the 3×3 block setting).
- The puzzle is solved when every light is off.
Playing Light Switch on Puzzle Solvers
- Choose a board, a switch shape and a difficulty, then press New Puzzle.
- Tap a square to flip it and its neighbours. Hover to preview what a press will flip.
- Pressed squares get a small green dot — pressing a square twice undoes it.
- Hint tells you the next press on the shortest way from where you are.
Using the Light Switch solver
- Choose the board size and switch shape, and click to set the lights (or press Sample).
- Press Solve: you get the shortest set of presses, one at a time, with the board after each press.
A worked example
On a 3×3 board with only the centre light on, pressing the four corners does it: each corner flips the centre’s neighbours… try it and see why the centre needs an odd number of presses around it.
Chasing on 5×5: if row 1 has lights at C2 and C4, press R2C2 and R2C4. Row 1 goes dark; now chase row 2 the same way.
Strategies
- Twice is nothing. Pressing a square twice undoes it, so never press the same square twice in a solution.
- Order doesn’t matter. The result depends only on which squares you press, not the order — so you can plan the whole solution as a set.
- Chase the lights. Work down from the top: for each light on in a row, press the square directly below it. The top rows go dark.
- Fix the bottom. After chasing, a pattern is left in the bottom row. Each pattern matches certain top-row presses; press those, then chase again.
- Use the maths. Each light gives an equation: the presses around it must add up to its state, counting mod 2. Solving those equations gives the shortest answer.
Common mistakes
- Pressing the same square twice — it cancels out.
- Chasing upwards instead of down, which undoes earlier work.
- Assuming every pattern can be solved — on some boards a few patterns are impossible.
Where it comes from
Switch puzzles like this go back to the 1980s, and became famous as handheld electronic games in the 1990s. Mathematicians love them because they are solved by linear algebra over the numbers 0 and 1.
Frequently asked questions
Can every pattern be switched off?
On some boards, yes; on others (5×5 with plus-shaped switches, for example) only about a quarter of all patterns can. Every puzzle the game makes is solvable.
What do the green dots mean?
They mark the squares you have pressed an odd number of times — handy for spotting double presses.
What is the shortest solution?
The solver finds the fewest presses by solving the light equations mod 2 and trying the few free choices.
How do I solve one from a book?
Open the Light Switch Solver, set the lights and press Solve.
Keep going
- Play Light Switcha fresh puzzle every time
- Light Switch Solverstep by step, every move explained
- Binary PuzzleFill the grid with 0s and 1s: never three the same in a row, half of each in…
- NimTake turns removing objects; play the right move and you can always win — the…
- Magic PathFind every number that fits the rule and join them all in one continuous path.
All guides: How to play every puzzle and game.