Numbered Walls in Akari: How to Solve Light Up From the Clues

The numbers on the black walls are the beating heart of every Light Up (Akari) puzzle. They're where almost every solve begins, and learning to read them fluently is the difference between staring at a grid and watching it light up. A wall numbered 0 hands you free eliminations; a wall numbered 4 hands you four free bulbs. In between lies a whole toolkit of deductions that, once you know them, make the numbered clues feel less like a constraint and more like a map. This guide explains exactly what each number means and the corner-and-edge tricks that turn the clues into placements. Want to test them as you read? Play a Light Up puzzle alongside, and check the rules if the basics are new.

What a numbered wall actually says

First, the one rule that powers everything: a numbered wall tells you exactly how many light bulbs must sit in the cells directly touching it — up, down, left, and right. Diagonal cells don't count. Not "at least," not "at most" — exactly that many.

So a wall showing 2 has precisely two bulbs among its orthogonal neighbours, no more and no fewer. Unnumbered black walls, by contrast, carry no constraint at all; they block light and that's it. The whole skill of clue-reading is comparing a wall's number against how many neighbouring cells it actually has available.

The numbers, one by one

0 — no bulbs allowed. The friendliest clue in the puzzle. A 0 means none of the wall's neighbours can be a bulb, so mark every adjacent cell as "no bulb" (×) immediately. Always clear the 0-walls first.

4 — all bulbs. The flip side. A wall can only show 4 if it sits in the interior with four open neighbours, and it means all four are bulbs. Place them at once. (Notice this is self-consistent: the wall sits between each opposite pair of bulbs, so they never light each other.)

1, 2, 3 — it depends on the room. These are the interesting ones, because their force depends entirely on how many neighbours the wall has. A 2 beside four open cells leaves you choosing two of four — not yet forced. But a 2 beside only two available cells forces both. The number alone never tells the whole story; you have to count the open neighbours.

The golden rule of clue-reading

Here's the principle that ties it together: when a wall's number equals the count of open cells still available beside it, every one of those cells is a bulb. When a wall's number is already satisfied, every remaining neighbour is a "no bulb."

Two moves, both forced:

• A 3 whose four neighbours include one wall (or one already-eliminated cell) has only three open neighbours left — so all three must be bulbs.
• A 1 that already has its single bulb placed means its other neighbours are all ×.

Run this check on every numbered wall after each change to the grid. As cells get eliminated by light rays elsewhere, walls that weren't forced a moment ago suddenly tip over into "fully determined."

Corners and edges do half your work

This is the trick experienced solvers lean on most. A numbered wall doesn't always have four neighbours:

• In the interior, a wall has 4 neighbours.
• On an edge, it has only 3.
• In a corner, it has just 2.

That shrinking neighbour count makes edge and corner clues unusually powerful. A corner wall numbered 2 has exactly two neighbours, so both are bulbs — instantly. An edge wall numbered 3 forces all three of its neighbours. Even a corner 1 is strong: with only two candidates, the puzzle quickly narrows to one. Whenever you see a numbered wall hugging the border, check it first — its geometry has already done most of the deduction for you.

Watch for clashing clues

Numbered walls also interact with each other, and spotting the clashes is a sharp technique. If two numbered walls share a neighbouring cell, the bulb in that shared cell counts toward both clues — which can force or forbid it. And the no-mutual-visibility rule sneaks in here too: if a wall's number would require two bulbs that can see each other down an open corridor, that arrangement is impossible, ruling out a candidate. Reading the numbers in combination, not in isolation, is what cracks the tighter grids.

From clues to a full solve

Numbered walls give you your opening and most of your forced moves, but they rarely finish a puzzle alone — especially on harder grids, where many walls are unnumbered. Once the clues run dry, you switch to illumination logic: excluding the cells your bulbs light, and finding dark cells that can only be lit one way. Our full strategy guide covers those moves, and the 5×5 walkthrough shows the numbered walls and illumination working together on a real grid.

So the next time a Light Up grid looks blank and intimidating, go straight to the numbers. Clear the 0s, force the 4s, check every clue against its neighbour count, and pay special attention to the corners and edges. The clues are a map — you just have to learn to read it. Play Light Up (Akari) now and start with the numbered walls.

Frequently asked questions

What do the numbers mean in a Light Up (Akari) puzzle?

A number on a black wall tells you exactly how many light bulbs must sit in the cells directly touching it — up, down, left, and right (not diagonally). A 0 means no adjacent bulbs, a 4 means all four neighbours are bulbs, and 1, 2, and 3 mean precisely that many. Unnumbered walls have no constraint.

How do you use numbered walls to solve Akari?

Compare each wall's number to how many open neighbours it has. When the number equals the count of open neighbours, all of them are bulbs; when the number is already met, the rest are "no bulb." Start with 0-walls (mark neighbours ×) and 4-walls (place all four bulbs), then re-check every clue as the grid changes.

Why are corner and edge clues important in Light Up?

Because walls on edges have only three neighbours and walls in corners have only two, their numbers force placements much faster than interior walls. A corner wall numbered 2 forces both its neighbours to be bulbs; an edge wall numbered 3 forces all three. Checking border clues first does a lot of the deduction for you.

Does a numbered wall mean "at least" that many bulbs?

No. A numbered wall means exactly that many bulbs sit in its orthogonal neighbouring cells — never more, never fewer. This precision is what lets you both place bulbs (when the number equals the open neighbours) and eliminate cells (once the number is already satisfied).