Light Switch Solver

Light Switch Solver — Step by Step

Click squares to switch on the lights of your puzzle, choose the switch shape, then press Solve. Or play a generated puzzle and send it here with one click.

Light Switch Solver: rules, how to use it, tips

Each press flips a square and its neighbours — find the presses that switch every light off.

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.

Using the 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.

Tips

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.

The full guide, with a worked example and common mistakes: How to play Light Switch.

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.