Light Up Solver (Akari)

Light Up Solver — Step by Step

Click a square to select it and click again to toggle a wall. Type 0–4 to number the selected wall, ■ for a plain wall, ⌫ to make it white. Then press Solve. Or play a generated puzzle and send it here with one click.

Light Up Solver: rules, how to use it, tips

Place bulbs so every white square is lit, bulbs never shine on each other, and every number counts the bulbs beside its wall.

The rules

A bulb lights its own square and every square in its row and column until a black wall blocks the light.
Every white square must be lit.
No bulb may be lit by another bulb.
A number on a black wall is how many bulbs sit directly next to it (across or down). Walls without numbers can have any number.

Using the solver

Choose the size, then click squares to make walls and type their numbers (or press Sample).
Press Solve and step through: numbered walls, squares with only one way to be lit, blocked squares and what-ifs.

Tips

Zeros and fours. A 0 means its neighbours have no bulbs. A 4 means all four neighbours do. A 3 against an edge has all its three free sides lit.
Only one way to light it. Find a dark square whose row and column offer only one possible bulb square — that square gets a bulb.
Bulbs light a lot. As soon as you place a bulb, every square it lights becomes bulb-free; mark them.
Numbers with no room to spare. A 2 with just two free neighbours gets bulbs in both.

The full guide, with a worked example and common mistakes: How to play Light Up.

Questions

Does a bulb light diagonally?

No — only along its row and column, until a wall.

What does ‘every wall numbered’ mean?

An easier version where every black wall shows its number, giving you more clues.

Can a bulb sit next to a 0?

No. A 0 wall has no bulbs on any of its four sides.

How do I solve a puzzle from a book?

Open the Light Up Solver, draw the walls and numbers, and press Solve.