Lights Out
A parity puzzle: pressing a cell flips it and the cells directly above, below, left and right. Switch every light off. Every board is generated from a known set of presses, so each one can be solved.
Turn every light off. Pressing a cell flips it and the cells directly above, below, left and right.
FreeOn this device
Solved on this device: 0 · move challenges met: 0. A hint marks the run as assisted.
Controls
- Tap or click a cell to press it.
- With the keyboard, Tab to the grid, move with the arrow keys and press Enter or Space.
- Undo takes back one press, Reset returns to the start, Hint shows a press that is part of a solution from where you are now.
The rules
- A press flips the pressed cell and its in-bounds orthogonal neighbours: corners flip 3 cells, edges 4, the middle 5.
- The puzzle is solved when every light is off.
- Pressing the same cell twice cancels out, and the order of presses never matters.
Scoring, saving and limits
Your press count is shown as you play. When the fewest possible presses has been proved — by checking every solution, which is possible for all boards here — it is shown after you finish, and the move challenge asks you to match it. Some boards have several solutions; none is called the only one.
Your current board, which puzzles you have solved and your move-challenge results are kept on this device only. Download a backup to move them; Clear this game deletes only Lights Out's data.
A run where you used a hint is marked as assisted and does not count as solved in your records.
Questions
- Can every board be solved?
- Every board here, yes: each is made by pressing a set of cells on a dark board, so pressing those same cells again solves it. Not every arbitrary pattern of lights is solvable on every size of board — that is why the boards are made this way.
- What does the hint actually tell me?
- One press that belongs to a fewest-presses solution of the board as it is now, worked out from the current lights rather than the original puzzle. Using it marks the run as assisted.
- Is the 'fewest possible' number a guess?
- No. The solver finds one solution and then tries every other solution the board has (on a 5×5 board there are four), keeping the shortest. If that check could not be completed the game would say “a solution”, not “the fewest”.