Lighting a room of walls
Akari, also known as Light Up, is a Japanese puzzle about placing bulbs in a grid broken up by black walls. Each bulb shines along its row and column until a wall or the edge stops it. Every white square must end up lit, no bulb may shine on another, and numbered walls fix how many bulbs sit in the four squares touching them.
Every bulb does two jobs: it lights squares, and it forbids bulbs on every square it lights. One good bulb often rules out a dozen squares.
Starting from the walls
The numbered walls are the best place to begin, especially the extreme ones.
- A 0. No bulb goes in any square touching it. Dot them all.
- A 4. All four squares touching it hold bulbs.
- Numbers that fill their space. A 3 against the edge of the board has only three squares beside it, so all three are bulbs. A 2 in a corner has only two, so both are bulbs. The same holds when other walls take up the missing sides.
- Numbers that are already met. As soon as a wall has its count, its number turns green. Dot every remaining square beside it.
Here is a worked example on the 7×7 Easy board. Say a wall marked 2 has three open squares beside it, but one of them is already lit by a bulb further along its row. A lit square can never hold a bulb, so that one is out. Two squares remain and the wall needs two bulbs, so both are bulbs. Place them, and watch which squares they light; any wall next to those squares just lost an option too.
Finding the last dark squares
Once the walls are worked through, switch your attention to the squares that are still dark. Every one of them must be lit by some bulb, and the question is which.
- Count the candidates. For a dark square, look along its row and column to the nearest walls. Every square in those two stretches could hold the bulb that lights it, unless it is already lit or dotted.
- One candidate left. If only one square could light it, that square is a bulb. This is the most common way to finish a board.
- Dots that need light. A dotted square still has to be lit, even though it cannot hold a bulb. If its row stretch is fully dotted or lit, the bulb must come from its column, and vice versa.
The dots matter here. A dot is only your note that no bulb goes there, but it turns a vague region into a short list of possibilities. Drag to spread them across rows you have ruled out.
Mistakes that slow players down
- Placing a bulb to light one square. A bulb also blocks its entire row and column stretch. Before placing one, check what it will forbid, especially near numbered walls.
- Forgetting unnumbered walls. A plain wall has no count, but it still blocks light. A bulb on one side of it cannot light the other.
- Over-satisfying a wall. A number turns red when it has too many bulbs beside it. Undo straight away; a red wall usually means a bulb elsewhere is wrong too.
- Missing a lone white square. A white square boxed in by walls on all four sides can only light itself. It must hold a bulb.
Working up through the sizes
Easy is a 7×7 grid. It is a good place to learn the wall openings and the one-candidate rule. Medium is 9×9 with a few more walls, so the open stretches get shorter and each bulb lights less, which means more squares to account for. Hard is 11×11 with the densest walls of the three, and there you will rely on dark-square counting far more than on the numbers.
A useful drill is to solve each board in two clear passes: first the walls, then the dark squares, repeating until done. When you use a hint, it first removes a bulb that does not belong, then places one the solution needs. Each puzzle has exactly one solution, so ask yourself which rule would have found that bulb. If you enjoy placing pieces under row and column limits, Star Battle at /games/star-battle offers a different take, with stars that must never touch.
