Akari Puzzles
A grid of walls and open cells. Place light bulbs so every open cell is lit, no bulb ever lights another, and every numbered wall ends up with exactly that many bulbs beside it. Tap a cell to place a bulb, tap again to mark it definitely empty, tap once more to clear it.
Also called Light Up.
Related Practice
What Is An Akari Puzzle?
Akari — also published as Light Up — is a grid of walls and open cells in which you place light bulbs. A bulb lights every open cell in its row and column until a wall blocks it or the grid edge is reached. Three rules decide where the bulbs can go: every open cell must end up lit, no bulb may ever light another bulb, and a numbered wall must have exactly that many bulbs in the cells touching it.
Like several of this site's other shading puzzles, it was popularised by the Japanese puzzle magazine Nikoli. The name in Japanese means roughly "light," which is a fair description of the whole mechanic — nothing about this puzzle is about shape or region, only about where a light can reach.
Every Wall Is Always Numbered
Published akari puzzles often leave some walls blank — a blank wall blocks light and gives no other information. This site numbers every wall instead, the same call shikaku makes for the same reason: difficulty should come from the grid itself, not from information the puzzle could have handed over for free. What changes the difficulty here is grid size and how many walls the grid carries — more walls means shorter open runs and more numbered footholds, which is genuinely easier, the same way a denser nonogram is easier than a sparse one.
Built From A Matching, Not A Search
A bulb anywhere in an unbroken run of open cells lights the WHOLE run, in either direction. So if every such run along the rows gets exactly one bulb, every cell is lit already — the only thing left to arrange is making sure no two of those bulbs end up sharing a column run too, which would mean they lit each other. That is a textbook matching problem, solved directly rather than searched for, and it is what actually builds every grid on this page: each row run is paired with a column run it can safely share a bulb with, and the pairing itself becomes the answer. The wall numbers are then read straight off that answer, and a grid is only shown once the numbers alone — without knowing the answer — are proven to pin down the very same one, by the same kind of deduction pass this site's other logic grids use.
What Actually Cracks An Akari
| Foothold | What it tells you | Why it works |
|---|---|---|
| A wall numbered 0 | None of its neighbours can be a bulb | The count around it must be exactly zero, which rules every touching cell out at once. |
| A wall whose need matches its options | Every undecided neighbour is a bulb | If a wall needs 2 and has exactly 2 undecided cells left, there is no other way to reach 2. |
| A wall already satisfied | Every other neighbour is empty | Adding one more bulb would push the count past what the number allows. |
| A cell nothing else could light | It must be a bulb itself | If every other cell that could ever light it is already ruled out, the light has to come from the cell itself. |
Show me the next move plays this exact sequence and names which foothold it is using, in the order a solver who is any good actually works in — never a guess dressed up as logic.
Akari Puzzles Frequently Asked Questions
What is an akari puzzle?
A grid of walls and open cells in which you place light bulbs so every open cell is lit, no bulb lights another, and every numbered wall holds exactly its count of bulbs. It is also called Light Up.
Why are all the walls numbered, unlike some published akari?
A blank wall only blocks light and tells you nothing else, so leaving some walls unnumbered would be withholding information rather than adding difficulty. This site numbers every wall and varies difficulty through grid size and wall density instead — the same call shikaku makes.
What is the best way to solve an akari puzzle?
Start with any wall numbered 0 — none of its neighbours can hold a bulb. Then look for a wall whose remaining need exactly matches its remaining options. Place a bulb, follow what it rules out along its row and column, and recheck the walls nearby.
Can two bulbs light each other?
No — a valid akari never has two bulbs sharing an unbroken row or column run. The board simply will not let you place one where it would.
Is akari the same as Light Up?
Yes — Light Up is the more common English name for the identical puzzle. Akari is the original Japanese name.
Is it free, and does it need an account?
Free, no account, no adverts, and nothing leaves your browser.