Light Up (Akari) Rules — How to Play

The complete light up puzzle rules, from the basic mechanics to advanced strategies. Includes a worked example and answers to common questions.

What is Light Up (Akari)?

Light Up — also known as Akari (あかり, Japanese for “light”) — is a logic puzzle created by Nikoli. Not to be confused with light-up jigsaw puzzles or 3D illuminated puzzles.

You get an N×N grid containing open (white) cells and walls (black blocks). Some walls display a number from 0 to 4. Your task: place light bulbs in the open cells so that every open cell is illuminated and no two bulbs can see each other.

The setup

A Light Up grid looks like this:

  ┌───┬───┬───┬───┬───┬───┬───┐
  │   │   │   │ ■ │   │   │   │
  ├───┼───┼───┼───┼───┼───┼───┤
  │   │ 1 │   │   │   │ 2 │   │
  ├───┼───┼───┼───┼───┼───┼───┤
  │   │   │   │   │ ■ │   │   │
  ├───┼───┼───┼───┼───┼───┼───┤
  │ ■ │   │   │ 0 │   │   │ ■ │
  ├───┼───┼───┼───┼───┼───┼───┤
  │   │   │ ■ │   │   │   │   │
  ├───┼───┼───┼───┼───┼───┼───┤
  │   │ 3 │   │   │   │ 1 │   │
  ├───┼───┼───┼───┼───┼───┼───┤
  │   │   │   │ ■ │   │   │   │
  └───┴───┴───┴───┴───┴───┴───┘

  ■ = unnumbered wall    [n] = numbered wall

White cells are open — you can place bulbs here. Black cells (■) are walls that block light. Walls may carry a number (like “0”, “1”, “2”, or “3”) that constrains adjacent bulb placement.

The three rules

Illumination. Each bulb lights its own cell and every cell in its row and column, extending in all four directions until blocked by a wall or the grid edge:
```
        ·
        ·
        │
        ·
  · · ──💡── · · · ·
        ·
        ■  ← wall blocks further light
```
Every open cell must be illuminated by at least one bulb. A cell lit by multiple bulbs (from non-conflicting sources) is fine.
No mutual visibility. Two bulbs cannot share a row or column unless a wall stands between them. If two bulbs can see each other — even across 10 empty cells — the placement is invalid:
```
  💡── · · ──💡  ← INVALID (bulbs see each other)
  💡── · ■ · ──💡  ← VALID (wall between them)
```
Numbered walls. A wall with a number tells you exactly how many bulbs must be placed in its orthogonal neighbors (up, down, left, right — not diagonal):
```
   ·  ·  ·
   · [2] ·   ← exactly 2 of the 4 adjacent cells must have a bulb
   ·  ·  ·

   Corner example:
   [2] ·     ← only 2 neighbors, both must have bulbs
    ·
```
0: No adjacent bulbs. 1–3: Exactly that many adjacent bulbs. 4: All four neighbors have bulbs. Unnumbered walls have no constraint on adjacent cells.

Worked example (5×5)

Walk through a small puzzle step by step:

Find 0-walls. Any wall marked “0” means all adjacent cells can be marked “no bulb.” Do this first — it is always safe and often cascades.
Check forced walls. Look for numbered walls whose remaining open neighbors exactly match their number. If a “2” wall has exactly 2 open neighbors, both must have bulbs.
Place bulbs and watch light rays. When you place a bulb, the light-ray visualization shows which cells are now illuminated. Check for visibility conflicts with existing bulbs.
Find isolated dark cells. After some bulbs are placed, some cells may only be reachable from one direction. The bulb must go in that position.
Verify walls. After placing all bulbs near numbered walls, confirm each has the correct count. The game shows satisfied walls with a green indicator.

On a 5×5 grid, 2 or 3 initial deductions usually cascade into the full solution.

Solving strategies

0-wall elimination

A wall marked “0” means none of its four orthogonal neighbors can have a bulb. Mark all adjacent cells immediately. When a numbered wall's quota is met, mark its remaining open neighbors too.

Forced wall placement

If a numbered wall has exactly as many open neighbors as its number, all must have bulbs. This is the most common deduction. Always re-check walls after any nearby cell is marked or filled.

Visibility exclusion

If placing a bulb in a cell would create a visibility conflict with an existing bulb (same row or column, no wall between), that cell cannot have a bulb. Mark it.

Isolated dark cells

An unlit cell that can only be reached by one possible bulb position forces that position. All other potential illumination sources are walls, grid edges, or already occupied. Enable the dark-cell highlight to spot these.

Corridor reasoning

A corridor (long unbroken row or column between walls) can hold at most one bulb. If cells within the corridor can only be lit from within, the bulb position within the corridor is forced.

Cross-constraint propagation

Combine wall constraints across multiple walls plus visibility exclusion. Two walls sharing an adjacent cell may jointly force or eliminate that cell when neither alone would resolve it.

Common mistakes

Forgetting light extends far. Bulbs illuminate in four directions until a wall, not just one cell away. A bulb can conflict with another 10 cells away if no wall is between them.
Ignoring distant dark cells. Cells in corridors far from any wall still need illumination. Do not forget them.
Not rechecking numbered walls. After placing a bulb near a numbered wall, re-verify its count. It is easy to accidentally over-constrain a wall.
Placing bulbs without checking the corridor. Before placing a bulb, scan its entire row and column for existing bulbs that would create a conflict.

Frequently asked questions

What is a Light Up (Akari) puzzle?

A logic puzzle where you place light bulbs on a grid so every white cell is illuminated. Bulbs shine along rows and columns until blocked by walls. No two bulbs can see each other. Some walls show a number indicating how many adjacent bulbs are needed.

What do the numbers on walls mean in Light Up?

A number on a wall (0–4) tells you exactly how many light bulbs must be placed in the cells directly above, below, left, and right of that wall. Not diagonally — only orthogonal neighbors count.

Can two bulbs be in the same row?

Yes, as long as there is a wall between them blocking line of sight. Two bulbs in the same row or column with no wall between them is a conflict.

Is Light Up the same as Akari?

Yes. Light Up is the English name, Akari (あかり) is the original Japanese name given by Nikoli. They refer to the same puzzle.

Do I need to guess in Light Up?

No. Every puzzle on The Puzzle Labs is solvable through pure logic. Einstein-level puzzles are certified to require no guessing or trial-and-error.

Related puzzle rules

Minesweeper rules — Uncover cells using number clues
Nonogram rules — Fill grid cells from row and column clues
Star Battle rules — Place stars with row, column, and region constraints

Play Easy Light Up