Light toggle puzzle online

In this light toggle puzzle you switch off all the lamps on a grid. Every click flips the chosen square and its neighbours above, below, left and right. Pick a grid from 3 × 3 to 7 × 7; every puzzle can be solved and the game tells you the minimum number of moves. No sign-up, works on phones.

Source: Wikipedia: Gaussian elimination over GF(2) (Loesbarkeit, Mindestzuege). Updated: 2 October 2026.

How it is calculated

In short: in the light toggle puzzle some lamps on a square grid are lit. Every click flips one lamp and its direct neighbours. Your goal: all lamps off, with as few clicks as possible.

How a move works

A click in the middle flips five squares: the square itself and four neighbours.
On an edge it is four, in a corner three.
Pressing the same square twice cancels out. The order of your clicks does not matter.

Solving strategy: chasing the lights

Work row by row: in each row press the squares under the lit lamps of the row above, until only the bottom row has lamps left. Then only a few patterns are possible; they tell you which squares of the top row you still have to press, and the chase starts again.

Why is every puzzle solvable?

Every puzzle here is made from a switched-off grid by random clicks, so it can always be undone. Not every distribution of lamps is solvable, for example a single lit corner on a 5 × 5 grid is not. The game works out the minimum with Gaussian elimination over the field with two elements; on 5 × 5 each puzzle has exactly four solution patterns and the shortest counts.

Grid sizes

Grid	Feel
3 × 3	Entry level, few possibilities
4 × 4	Many equally good solution paths
5 × 5	The classic size
6 × 6 and 7 × 7	Bigger, the solution is unique

Puzzle series

“Next puzzle” takes you through a numbered series. Grid and number define the puzzle exactly. Your progress stays on your device only; puzzles where you used the hint do not count.

Frequently asked questions

How does the light toggle puzzle work?

A grid holds lamps that are on or off. A click flips the chosen square and its neighbours above, below, left and right. You win when all lamps are off.

Is every light toggle puzzle solvable?

Here, yes, because the puzzles are made from a switched-off grid by random clicks. In arbitrary lamp patterns some positions on 4 × 4 and 5 × 5 are unsolvable.

How many moves are needed at minimum?

The game works it out for every puzzle with linear algebra and shows it as “Minimum”. It counts your own moves next to it.

How do I get started?

Chase the lights down row by row: press the square under each lit lamp. What is left in the last row tells you how to correct the top.

Is anything saved?

Only which puzzle numbers you solved, and only in your browser (localStorage). Nothing is sent anywhere.

Sources and legal basis

As of: 2 October 2026 · Editorial policy