How to Solve Light Up (Akari) Puzzles: Strategies and Techniques

Light Up — known in Japan as Akari — looks almost too gentle to be a real challenge: just drop some light bulbs on a grid until everything is lit. Then you hit a puzzle where the bulbs seem to have nowhere safe to go, every placement risks a conflict, and a stubborn dark cell refuses to brighten. The way through isn't luck; it's a small set of reliable techniques built around the puzzle's three rules. Learn them and even sparse, tricky grids open up by pure logic. This guide covers the core Light Up (Akari) solving strategies, from the moves you'll use on every puzzle to the deductions that crack the hard ones. Follow along on a real grid — play a Light Up puzzle as you read, and skim the rules first if they're new.

The three rules, in one breath

Every technique flows from the same setup. You place light bulbs in the white cells of a grid dotted with black walls, so that: every white cell is lit (a bulb shines along its row and column until a wall or the edge stops it), no bulb lights another bulb (no two bulbs share a row or column with a clear line between them), and every numbered wall has exactly that many bulbs touching it (orthogonally — up, down, left, right). Unnumbered walls carry no constraint. Those three rules are the whole game.

Technique 1: Start with the 0-walls

The single easiest deduction in Akari comes from walls numbered 0. A 0 means no bulb may sit next to this wall, so you can immediately mark every cell orthogonally adjacent to it as "no bulb" (an ×). It's free information, and it shrinks the candidates around that wall to nothing.

Sweep the grid for every 0 first and cross out their neighbours. On many puzzles this single pass removes a surprising number of cells from contention and sets up the next round of deductions.

Technique 2: Force the full walls

The mirror image of the 0-wall is the fully-determined wall — a numbered wall whose clue equals the number of open cells still available beside it. The clearest case is a 4: a wall numbered 4 (only possible in the interior, where it has four neighbours) means all four adjacent cells must be bulbs. Place them.

The same logic scales to any number. If a wall shows 3 and one of its four neighbours is a wall or already marked ×, then its three remaining open neighbours must all be bulbs. In general: when a wall's clue equals its count of open neighbours, every one of them is a bulb. Numbered walls on edges and in corners are especially powerful here, because they have fewer neighbours to begin with, so their clues lock down faster.

Technique 3: Watch the edges and corners

A numbered wall doesn't have four neighbours everywhere. On an edge it has three; in a corner it has only two. That makes edge and corner clues unusually constraining:

• A corner wall numbered 2 has exactly two neighbours, so both are bulbs — instantly forced.
• An edge wall numbered 3 has three neighbours, so all three are bulbs.
• A wall numbered 1 with all but one neighbour already eliminated forces a bulb in the last open neighbour.

Always check what each numbered wall actually has room for, not just its number. The geometry around it does half your work.

Technique 4: Use light-ray exclusion

Once bulbs start going down, the no-mutual-visibility rule becomes a tool, not just a restriction. Any cell that already lies in a bulb's line of sight can never hold a bulb — placing one there would mean two bulbs lighting each other. So the moment you place a bulb, mark the cells it illuminates as "no bulb."

This is where the light-ray view earns its keep: every cell a bulb lights is a cell that's now off-limits for future bulbs. Tracing those rays down long corridors eliminates candidates far from the bulb itself, which is how progress spreads across a sparse grid.

Technique 5: Light the last dark cell

Here's the deduction that finishes hard puzzles. The illumination rule says every white cell must end up lit, so consider a cell that can only be reached by a bulb from a small number of positions. If there's exactly one cell that could light a particular dark cell, a bulb must go there — there's no other way to satisfy the rule.

The strongest version: a white cell that has no open cell in its entire row-and-column corridor except itself must be a bulb, because nothing else can light it. Hunting for cells that are "running out of ways to be lit" is the key to unlocking grids where the numbered walls have gone quiet — which, on harder puzzles, is most of the grid.

A reliable solving order

Put it together and you have a dependable routine for any Akari:

1. Mark every 0-wall's neighbours with ×.
2. Resolve the forced walls — 4s, edge and corner clues, and any wall whose number equals its open neighbours.
3. After every bulb, exclude its light rays (mark the lit cells "no bulb").
4. Hunt for dark cells that have only one possible bulb to light them, and place those bulbs.
5. Repeat, re-scanning after each placement; use the dark-cell view to spot what's still unlit.

Work in passes rather than fixating on one corner. Akari tends to unlock in cascades: one forced wall lights a region, the exclusions ripple out, and a dark-cell deduction opens the next.

The golden rule: never guess

The most important habit is a mindset. A well-made Light Up puzzle has exactly one solution reachable by pure logic, so if you feel like guessing, there's a deduction you've missed. Step back, re-check the numbered walls, and look for a dark cell that's running out of options. That patience is what our hardest Einstein puzzles are built around — certified solvable without a single guess.

The fastest way to make these techniques automatic is to use them. Play a Light Up puzzle now, start by clearing the 0-walls, and watch the grid light up. To go deeper on the clue logic, see our guide to numbered walls in Akari, or follow a full 5×5 walkthrough.

Frequently asked questions

How do you solve a Light Up (Akari) puzzle?

Work by elimination and forcing. Start by marking the neighbours of every 0-wall as "no bulb," then place bulbs forced by numbered walls (a 4 forces all four neighbours; edge and corner clues force faster). After each bulb, mark the cells it lights as off-limits, since no two bulbs may light each other. Finally, find dark cells that can only be lit from one position and place those bulbs.

What is the best strategy for Akari?

Begin with the most constrained clues — 0-walls and high-numbered walls, especially on edges and corners where they have fewer neighbours. Then alternate two moves: exclude the light rays of every bulb you place, and hunt for cells that are running out of ways to be lit. Re-scan after each placement so eliminations cascade.

Do you have to guess in Light Up puzzles?

No. A properly made Light Up (Akari) puzzle has a single solution reachable by logic alone. If you feel stuck, there's a deduction available — usually a numbered wall you haven't fully used or a dark cell with only one possible bulb to light it — rather than a need to guess.

What does a 0 mean in a Light Up puzzle?

A wall numbered 0 means no light bulb may be placed in any cell orthogonally adjacent to it. It's the easiest deduction in the puzzle: simply mark all of that wall's neighbouring cells as "no bulb." Clearing every 0-wall first is the standard opening move.