Akari Number 0 Strategy — How to Solve Number 0 Cells

What a Number 0 Cell Tells You

A wall cell numbered 0 is a hard prohibition: exactly 0 of its four orthogonally adjacent cells (up, down, left, right) may hold a light bulb. Every open neighbor gets an immediate ✗ mark — it can never contain a light. It is the fastest deduction in the game, which is why reading 0s first is a universal Akari habit.

Unlike numbers 1–4, a 0 never gives you a bulb placement of its own. Its power is elimination: each neighbor it clears shrinks the space where remaining bulbs can go, and in narrow corridors that alone can force a bulb one cell further out.

Why 0 Cells Come First

Scan the whole grid for 0s before placing anything. On a typical GridPaw Easy board (6×6) two or three 0 cells can clear a third of the board's impossible spots in under a minute — no other clue produces that many provable marks that fast. On the 10×10 Daily Challenge, a full 0-sweep is the standard opening move for the same reason.

After each 0 is marked, re-check the cells that just lost a possible light source. A white corner cell with only two open neighbors, one of them now ✗'d, leaves exactly one direction a bulb can come from — a forced placement. This "0s first, then read forced lighting" loop is the engine behind most Easy and Medium solves.

Worked Example: A 0 in a Corner

Take a 5×5 grid with a 0 wall in the top-left corner. That corner has only two neighbors — right and down — and both get ✗ marks. Now look at the white cell diagonally below-right of the corner. Its only neighbors are a wall (the 0), a ✗ cell, the cell below it, and the cell to its right. If the right neighbor is also blocked by a wall, the below neighbor becomes the sole possible light source, so a bulb there is forced.

The same reasoning scales to edges: a 0 on the top row blocks all three of its open neighbors. In GridPaw, mark those cells with a paw print note (right-click on desktop, long-press on mobile) so the game tracks your deductions for you.

How a 0 Interacts With Other Clues

0 next to a numbered wall: the numbered wall is a wall, so it was never a bulb candidate — the 0 only blocks white cells.
0 sharing a neighbor with a 2: the shared cell is ✗ for the 0, so the 2 must fit both of its bulbs into its remaining neighbors, often forcing both.
0 and 4 in the same block: a 4 forces bulbs in all four neighbors while a 0 forbids them. Together on a small board they can fully determine the lighting of that section.
0 as a guard: a 0 beside a long wall segment protects that whole segment from bulb placement, which makes line-of-sight tracing along the wall much easier.

Common Mistakes With 0 Cells

Marking the 0 cell itself: the 0 is a wall — it never holds a bulb and never needs to be lit. Only its neighbors are affected.
Forgetting line of sight: ✗ cells can still be lit, they just can't hold a bulb. A bulb placed at the end of a row still illuminates every ✗ cell between it and the wall.
Skipping the follow-up: marking four neighbors and moving on misses the payoff. Re-scan for cells whose only remaining light path was just eliminated — those are your next forced bulbs.

FAQ

What if a 0 has fewer than 4 open neighbors?

Walls and the grid edge don't count as neighbors, so the prohibition simply covers the open ones. A corner 0 blocks only two cells; an edge 0 blocks three.

Can a 0 cell ever contain a bulb?

No. Numbered cells are walls in Akari — they block light and never hold bulbs. The 0 tells you about its neighbors, never about itself.

Is a 0 still useful after its neighbors are marked?

Yes. Recheck the ✗ cells: if a white cell can now only be lit from one direction, that direction is a forced bulb. The 0 keeps paying off for the rest of the solve.

Where can I practise 0 reads?

Start on Easy 6×6 boards, where 0s appear often enough to build the habit, then move to the Daily Challenge. Or use the Hint button on any GridPaw puzzle when a 0's follow-up isn't obvious — it reveals the next logical placement.