Lights Out
Tap a light to flip it together with its neighbors and turn the whole board off, and every board is guaranteed solvable.
FAQ
Why is every board solvable?
What happens if I tap the same cell twice?
Is there a general strategy?
Where are my scores kept?
How to use
- Learn the rule
Tap any cell and it flips together with its four orthogonal neighbors, lit to dark and dark to lit.
- Read the board
A few lights start on. Find the clusters first, since working a crowded region pays off fastest.
- Chase row by row
The classic light chasing method: from the second row on, tap the cell below every lit cell above, pushing all lights toward the bottom.
- Finish and improve
The last row has only a handful of fixed endings. After clearing, chase a lower move count or take on a bigger board.
About this tool
Lights Out is a puzzle with one line of rules and real depth: every light is either on or off, tapping one flips it with its neighbors, and the goal is a fully dark board. Three sizes from 4×4 to 6×6 are available, and every opening is generated by tapping from the all-off state, so every board is guaranteed to have a solution with no dead ends. The board sizes give a gentle ladder, and every round takes only a minute or two to clear.
The joy comes from discovering the algebra behind flipping: a tap is its own inverse, order never matters, and only the parity of taps per cell decides the outcome. Once that clicks, trial and error stops being random and solving becomes systematic. Best move counts are stored per size, so after the first clear you can chase a tighter solution or move up to a bigger grid. Random openings keep the puzzle fresh across sessions, so the same ideas get tested again and again.
The guaranteed solution comes from how boards are made. Generation starts from the all-off state and applies a handful of random taps, which is building the answer first and shuffling it afterwards. Every opening therefore returns to darkness, and no dead boards exist. If a scramble happens to finish fully dark, the generator rerolls it, so a board always opens with lights on. Best move counts are stored for the 4 by 4, 5 by 5 and 6 by 6 sizes, so switching grids never mixes records.
How it works
Under the hood the game is linear algebra over two values: the board is a matrix of zeros and ones, tapping a cell adds a cross shaped basis vector, and the goal is reducing the opening to zero. Addition commutes, so order is irrelevant and each cell has only two choices, tapped or not. Solvability depends on whether the opening lies in the span of those vectors, and because boards are generated from all-off by taps, they always do.
Light chasing exploits the locality of flips: a lit cell in one row can only be darkened by tapping the cell below it, so sweeping from the top pushes all uncertainty into the final row. On 5×5 that last row has thirty three possible states with a limited set of solvable endings, easily handled by a lookup. Larger boards add freedom to the span, which is exactly why 6×6 and beyond feel harder and reward more thought.
A tap is its own inverse because the flip is an exclusive-or: one tap toggles the five-cell cross, and two taps restore it exactly. Since the generator builds each board by tapping, replaying its taps verbatim always solves the board, and the cleverest solution only ever comes in lower. The 6 by 6 grid carries more freedom than 5 by 5, yet solvability holds for the same reason. Only the final-row table grows with it. Records are kept per size, so a 5 by 5 best never competes with a 4 by 4 one.
When to use it
- Commuting warmup
A 5×5 board is the right dose of thinking for a queue or a train ride. One or two boards fit into a short break, waking the brain up without dragging you into a video feed. The pause friendly design means an interrupted board never costs you anything.
- Logic play for kids
The rule takes one sentence to explain and the trial and error starts immediately. Guiding a child to notice which cells flip together gently builds the habit of thinking before tapping, a cheap and effective teaching tool. Watching five cells flip together is the first aha moment worth waiting for.
- Algebra practice for puzzle fans
Treat each board as a linear system and derive your own solvability rules beyond light chasing. The three sizes form a difficulty ladder where the clear is only the beginning and the minimum move count is the real target. Each size stretches the same idea further without adding new rules.
- Climbing the sizes
Learn the cross-flip feel on 4 by 4 and drill light chasing on 5 by 5. Save 6 by 6 for a stubborn day; records stay separate per size, so each grid keeps its own curve.
Tips & tricks
- Tapping the same cell twice cancels out, so experiment boldly and undo with a second tap.
- Light chasing solves any board: push the lights downward row by row, then finish the last row with a fixed table.
- Deal with clusters before lone lights, since the chain reactions often clear the strays for free.
- Master 5×5 before moving up; parity intuition forms fastest on the middle size.
- Open on the row holding the most lights; light chasing starts from row two, and that first-row choice decides your move count.
Things to watch
- Chasing single lights
Poking around to darken one lamp tends to light another, and the move count climbs. Zoom out to whole rows and follow a row by row plan instead. A whole row plan beats scattered pokes every single time. Cluster rows first, then sweep the stragglers with the same motion.
- Forgetting taps are reversible
Being afraid to retap a cell traps you without experiments. A second tap restores everything, so the right posture is bold tries and clean reverts. The second tap is a free undo, so there is nothing to fear. Experiments and reverts cost exactly the same, so use both freely.
- Ignoring parity
Hunting for a better order is wasted effort because only the parity per cell matters. Once you accept that, the temptation to reshuffle sequences disappears. Accepting this saves a pile of pointless retries. Parity first, order second, and the solution follows.
- Memorising the big board
The 6 by 6 final row holds far more states than 5 by 5, and rote memorisation pays badly there. Master the 5 by 5 endings first, then push the same reasoning into the bigger table.