How to play Lights Out
The game is played on a 5 by 5 grid of lights. At the start of each level some of the lights are on. Your aim is to turn every light off.
Pressing a square flips that light and the lights directly above, below, left and right of it. Lights that were on go off and lights that were off come on. Diagonal neighbours are not affected, and squares on the edge of the board simply have fewer neighbours to flip.
- Level: each new level is built by pressing a set of random squares on a dark board, so it can always be solved. Level 1 uses three presses, and every level after that adds one more, up to a maximum of sixteen.
- Moves: counts how many presses you have made on the current level.
- Lit: shows how many lights are still on.
- Best: the highest level you have cleared, saved in this browser.
Clear the board to see how many moves you took, then press Next level. Use Reset level to restore the starting pattern and your move count, or Start over to go back to level 1. The Hint button highlights one square that is part of a working solution from the current position.
Controls
| Desktop | Click a light to press it. After clicking the board, the arrow keys move a highlight and Space or Enter presses the highlighted light. |
|---|---|
| Mobile | Tap any square on the grid to press it. Use Hint if you get stuck, and Reset level to try the same puzzle again. |
Tips and strategy
Order does not matter
The most useful fact about this puzzle is that the order of presses makes no difference to the final result. Pressing A then B gives exactly the same board as pressing B then A. It also follows that pressing the same square twice cancels out completely. So a solution is really just a set of squares, each pressed once.
Chase the lights down
A simple method that always makes progress is called chasing:
- Look at the top row. For every light that is on, press the square directly below it in the second row. This turns the top row completely off.
- Now do the same for the second row by pressing squares in the third row, and continue down the board.
- When you finish, only the bottom row may still have lights on.
Fixing the bottom row
The pattern left in the bottom row tells you which squares of the top row to press before chasing again. Some useful pairs, reading the bottom row from left to right, where X is a lit light:
- X X X . . : press the second square of the top row.
- X X . X X : press the third square of the top row.
- X . X X . : press the fifth square of the top row.
- . X . X . : press the first and fourth squares of the top row.
After pressing those top squares, chase the lights down once more and the board will clear. It is not always the shortest route, but it is reliable.
Look for shortcuts
Early levels are made from only a few presses, so look for tell-tale plus shapes. A cross of five lit squares means one press in its centre will clear it. Spotting these shapes lets you finish in far fewer moves than chasing.
About Lights Out
Lights Out is a well-known type of grid puzzle in which each button toggles itself and its neighbours. The idea appeared as a handheld electronic game in the 1990s, and the puzzle has been studied by mathematicians ever since, because it can be described neatly using linear algebra where every value is simply on or off.
That mathematics explains some surprising facts. On the 5 by 5 board, not every pattern of lights can be switched off, and every pattern that can be solved has four different solutions. Pressing any square an even number of times is the same as not pressing it at all.
Our browser version creates every level by pressing squares on a dark board, which guarantees the puzzle can be solved. It is built from scratch for PlayNook and runs entirely on your device.
Frequently asked questions
Can every level be solved?
Yes. Each level is created by pressing random squares on an all-dark board, so undoing those presses will always turn every light off.
How does the Hint button work?
It highlights one square that belongs to a solution from your current position. Press the highlighted square and ask again for the next one if needed.
Does it matter what order I press the squares in?
No. The final board depends only on which squares were pressed an odd number of times, not on the order of the presses.
What does Reset level do?
It restores the level to its starting pattern and resets your move count to zero, so you can try for a cleaner solution.
