Light Switches
Each press toggles a lamp and its neighbours: switch everything off.
The famous light puzzle, from 5 × 5 to 9 × 9. Grids are always solvable, the shortest solution is computed with binary algebra, and an AI switches the board off before your eyes.
- Players
- 1 player
- Length
- 2 to 15 min
- Solo
15 days of full access, no account · No download
How to play
Goal
Switch off every lamp on the board.
How it works
- Pressing a lamp toggles it (on or off), along with its four direct neighbours: above, below, left and right.
- Each press counts as one move; the timer starts on the first press.
- The order of the presses does not matter, and pressing the same lamp twice cancels the effect: a shortest solution therefore never uses the same lamp twice.
- Every grid is solvable: they are built from hidden presses.
Levels
- Easy: 5 × 5, 5 to 8 presses.
- Medium: 6 × 6, 9 to 13 presses.
- Hard: 7 × 7, 14 to 20 presses.
- Expert: 8 × 8, 20 to 28 presses.
- Devilish: 9 × 9, about thirty presses (at least 28).
The “Symmetric” option produces regular patterns (mirror, rotation); “Random” scatters the hidden presses.
About the AI
The board translates into a system of linear equations over GF(2), the field with two elements: one unknown per lamp (press or not), one equation per lamp (it must change state an odd number of times if it is lit). The AI solves it by Gauss-Jordan elimination, then goes through all the equivalent solutions (the 5 × 5 has 4, the 9 × 9 has 256) to keep the shortest. The hint points to a lamp in this optimal solution; the “AI solves” button applies all of it.
Records are only registered without hints or AI help.
Difficulty levels
- Easy5 × 5: 5 to 8 presses are enough.
- Medium6 × 6: 9 to 13 presses.
- Hard7 × 7: 14 to 20 presses.
- Expert8 × 8: 20 to 28 presses.
- Diabolical9 × 9: about thirty presses, and 256 equivalent solutions to choose between.
