Lights Out Solver | Copy the Board to See Which Lights to Press (Minimum Moves), 3×3 to 10×10, 2 or 3 Colours, 8-Neighbour Mode, Light Chasing Chart, Solvable Share and Minimum Moves for an All-Lit Board
The Lights Out Solver answers questions such as “which lights do I press to clear this Lights Out?”, “how many moves does the all-lit 5×5 take?” and “is this board even solvable?”. Copy the board from a game puzzle or an electronic Lights Out by tapping cells, and every cell you need to press gets a red circle, along with the minimum number of moves and their positions (A1, C3 and so on). The answer is recalculated after every press, so you can use it from the middle of a puzzle. Unsolvable boards (three quarters of all 5×5 patterns) are marked as unsolvable, so you can spot copying mistakes. Boards from 3×3 to 10×10 are supported (rows and columns from 2 to 10 separately), toggling either the plus shape (up, down, left, right) or all 8 neighbours, with 2 colours (on and off) or 3 colours that advance with each press. There is a mode for playing random puzzles, plus undo, a hint (press one move) and a light chasing button that pushes the lights down from the top row. For solving by hand it includes the chart of “pattern left on the bottom row → cells to press on the top row” (7 patterns for 5×5), a table of nullity, the share of solvable boards and the minimum moves to clear an all-lit board by size (15 for 5×5), and an explanation of the terms and how it works.
Lights Out solver
Tap to copy your puzzle's board and the cells to press to clear it (in the fewest moves) appear straight away. You can also play random puzzles.
Board size
Cells that change when pressed
Number of colours
Minimum moves left
1
Lit cells
5 / 25
Moves made
0
Ways to press
4
Nullity 2
Cells to press (moves: 1): C3
You can press them in any order. Columns are A, B, C… from the left and rows are 1, 2, 3… from the top.
Light chasing chart (solving by hand)
The classic way to solve by hand without the answer. ① Working down from the top row, press the cell directly below each lit cell to push the lights to the bottom row. ② Find the pattern left on the bottom row in the table below and press the red cells on the top row. ③ Push down once more and every light goes out.
| Lights left on the bottom row | Cells to press on the top row |
|---|---|
This table is for 5×5 (2 colours, plus shape). If the bottom-row pattern is not in the table, the board cannot be solved. The table is rebuilt when you change the board size.
Solvable share and minimum moves by board size
Calculated with the number of colours and toggling pattern you have chosen. With a nullity of 0, every board can be solved.
| Size | Nullity | Share of solvable boards | Minimum moves from all on |
|---|---|---|---|
| 3×3 | 0 | All | 5 |
| 4×4 | 4 | 1/16 | 4 |
| 5×5 | 2 | 1/4 | 15 |
| 6×6 | 0 | All | 28 |
| 7×7 | 0 | All | 33 |
| 8×8 | 0 | All | 40 |
| 9×9 | 8 | 1/256 | 25 |
| 10×10 | 0 | All | 44 |
Terms and how it works
- Lights Out
- A puzzle where pressing a cell toggles it and the cells above, below, left and right of it. You win when every light is off. It comes from an electronic game released by Tiger Electronics in 1995 and turns up as a puzzle in many video games
- Order of presses
- Does not matter. Whatever order you press in, the board ends up the same as long as each cell is pressed the same number of times
- The same cell twice
- Pressing twice undoes it, so an answer only has to say whether to press each cell or not (0 to 2 times with 3 colours)
- Light chasing
- Working down from the top row, press the cell directly below each lit cell to push the lights down. Only the bottom row is left, so press the top row as the chart says and push down again
- Nullity
- How much freedom there is in choosing an answer. At 0, every board can be solved in exactly one way. 5×5 has 2, so only 1/4 of boards are solvable, and each solvable board has 4 ways to press
- Quiet patterns
- Sets of presses that leave the board unchanged (they exist when the nullity is 1 or more). Adding one to an answer still gives an answer, so the tool picks the one with the fewest presses
The answer comes from solving a system of linear equations, with the number of presses on each cell as the unknowns, by Gaussian elimination (arithmetic modulo 2 for 2 colours and modulo 3 for 3 colours). When there are several ways to press, all of them are compared and the one with the fewest presses is shown.
ABOUT
About Lights Out Solver | Copy the Board to See Which Lights to Press (Minimum Moves), 3×3 to 10×10, 2 or 3 Colours, 8-Neighbour Mode, Light Chasing Chart, Solvable Share and Minimum Moves for an All-Lit Board
The Lights Out Solver shows which cells to press, and the minimum number of moves, to turn off every light once you copy a Lights Out board. It supports 3×3 to 10×10, 2 or 3 colours, and plus or 8-neighbour toggling, and tells you when a board cannot be solved.
How to use Lights Out Solver | Copy the Board to See Which Lights to Press (Minimum Moves), 3×3 to 10×10, 2 or 3 Colours, 8-Neighbour Mode, Light Chasing Chart, Solvable Share and Minimum Moves for an All-Lit Board
- 1Choose the board size (5×5, etc.), which cells change when you press (plus shape or all 8 neighbours) and the number of colours
- 2With “Enter the board (copy the puzzle)” selected, tap the lit cells until the board matches your puzzle (with 3 colours, each tap advances the colour)
- 3Press the cells with red circles and every light goes out. The cells to press are also listed by position (A1, C3, etc.) with the minimum number of moves
- 4To try it for real, switch to “Press to play”. You can also go one move at a time with “Hint (press one move)”
- 5To practise solving by hand, press “Push down (light chasing)” and look up the pattern left on the bottom row in the chart
Great for
- When a Lights Out style puzzle in a video game has you stuck
- Finding the answer to an old electronic Lights Out game or a Lights Out app
- Checking whether the board you copied can really be solved (or whether you copied it wrong)
- Finding the minimum moves for classic boards such as the all-lit 5×5
- Practising solving by hand without the answer, using the light chasing chart
- Using it as teaching material for systems of linear equations and matrices (arithmetic modulo 2)
Good to know
- Pressing a cell toggles that cell and the cells above, below, left and right of it (and the diagonals too if you choose 8 neighbours). The order of presses does not matter, and pressing the same cell twice undoes it, so the answer is simply which cells to press.
- The answer comes from solving a system of linear equations, with the number of presses on each cell as the unknowns, by Gaussian elimination modulo 2 (2 colours) or modulo 3 (3 colours). When there are several ways to press, all of them are compared and the one with the fewest presses is shown (if there are more than 65,536 combinations, minimality is not checked).
- A 5×5 board (2 colours, plus shape) has a nullity of 2, so only 1/4 of the 2^25 light patterns can be solved, and each solvable board has 4 ways to press. On 3×3, 6×6, 7×7, 8×8 and 10×10 every board can be solved, in exactly one way.
- The light chasing chart is only built for 2-colour, plus-shape boards with 8 columns or fewer. It is recalculated for the size you choose.
- Some games use different rules, such as changing only the surrounding cells and not the pressed cell itself. In that case this tool's answer will not match.
Questions this tool answers
Use Lights Out Solver | Copy the Board to See Which Lights to Press (Minimum Moves), 3×3 to 10×10, 2 or 3 Colours, 8-Neighbour Mode, Light Chasing Chart, Solvable Share and Minimum Moves for an All-Lit Board for searches like these:
- Learn how to solve Lights Out
- Find the answer (which cells to press) for a Lights Out board
- Find the minimum moves for the all-lit 5×5 Lights Out
- Check whether a Lights Out board can be solved
- See the light chasing chart
- Beat a Lights Out puzzle in a video game
FAQ
- How many moves does the all-lit 5×5 Lights Out take?
- 15 moves at minimum. There are 4 ways to press, and one of them is B1, C1, E1, B2, C2, D2, C3, D3, E3, A4, B4, D4, E4, A5, B5 (columns A to E from the left, rows 1 to 5 from the top).
- How do I solve a 3×3 Lights Out?
- Every 3×3 board can be solved, and there is only one way to press. For the all-lit board, press the four corners and the centre (A1, C1, B2, A3, C3). When only the centre is lit, press the centre and the four cells above, below, left and right of it.
- Are there unsolvable Lights Out boards?
- Yes. On 5×5, three quarters of all light patterns cannot be solved; for example, a board with only one corner lit can never be cleared. Only 1/16 of 4×4 boards and 1/256 of 9×9 boards can be solved. If the tool says “unsolvable”, check that you copied the board correctly.
- What is light chasing?
- It is the classic way to solve by hand without looking at the answer. Starting from the top row, press the cell directly below each lit cell to push the lights down to the bottom row. Look up the pattern left on the bottom row in the chart, press the given cells on the top row, and push down once more to clear everything. On 5×5, when the bottom row is “●○○○●”, press the 1st and 2nd cells from the left on the top row.
- What if only the centre cell of a 5×5 is lit?
- It takes 11 moves (B1, C1, E1, A2, E2, A3, C3, D3, C4, A5, B5). Even a single light takes surprisingly many moves, because every press also affects the cells around it.
- Does it work for 3-colour Lights Out?
- Yes. Choose “3 colours (each press advances the colour)” and each press moves the pressed cell and its neighbours through off → cyan → pink → off; the tool finds the presses that turn every cell off. Some answers press the same cell twice, and those cells are marked “×2”. An all-cyan 5×5 board takes 18 moves.
Special Thanks