Akari Puzzle Rules — Complete Light Up Guide

GridPaw is a cat-themed version of Akari (also known as Light Up), a classic logic puzzle created by Nikoli in Japan. Understanding the rules is the first step to mastering the game.

The Grid

GridPaw is played on a grid of white cells and black cells. Your goal is to place light bulbs on white cells so that every white cell is illuminated.

5 Core Rules

1. Place bulbs on white cells — tap a white cell to place or remove a bulb. On GridPaw, bulbs are represented by cute cats 🐱.
2. Bulbs illuminate their row and column — light travels in straight lines until blocked by a black cell or the grid edge. Every white cell in that path is considered "lit."
3. No two bulbs can see each other — two bulbs in the same row or column with no black cell between them is illegal. This is the trickiest rule for beginners.
4. Numbered black cells are clues — a black cell with a number tells you exactly how many of its 4 orthogonal neighbors (up, down, left, right) must contain bulbs. For example, a "2" means exactly 2 of its 4 neighbors have bulbs.
5. All white cells must be lit — every white cell on the grid must be illuminated by at least one bulb. If any white cell remains dark, the puzzle is not solved.

Rule Examples

Here are concrete examples of how the rules work in practice:

Example: Number 4 Cell

A black cell marked 4 has exactly four adjacent white cells (up, down, left, right). All four must contain bulbs. Place them immediately — this is the most powerful forced placement in any Light Up puzzle.

Example: Number 0 Cell

A black cell marked 0 means none of its four adjacent white cells can have a bulb. Mark all four neighbors with an X. This is equally powerful — it eliminates multiple positions at once.

Example: Number 2 Cell with Blocked Neighbors

If a black cell marked 2 has two of its four neighbors already blocked by X's (from other deductions), exactly 2 of the remaining 2 open neighbors must be bulbs. Both are forced — place them.

Example: Line-of-Sight Conflict

Imagine a bulb at position (row 2, column 3). It lights all white cells to its left until a black wall or the grid edge. If another bulb is placed at (row 2, column 5) with no black cell between them, the two bulbs see each other — this is a rule violation. The second bulb must be removed or placed elsewhere.

Common Rule Misconceptions

• Myth: Bulbs light diagonally. No — bulbs only light orthogonally (up, down, left, right). Diagonal cells are never illuminated by a bulb.
• Myth: Black cells need to be lit. No — only white cells need illumination. Black cells are walls and do not need light.
• Myth: Numbered cells are hints, not rules. No — the number on a black cell is a hard constraint. Exactly that many neighbors must have bulbs. No more, no less.
• Myth: You can place bulbs on black cells. No — bulbs can only be placed on white cells. Black cells block light but cannot hold bulbs.
• Myth: A puzzle has multiple solutions. Well-constructed Akari puzzles have exactly one valid solution. If you find two valid configurations, you missed a deduction.

FAQ