How to play Light Up
Place bulbs so every white square is lit, bulbs never shine on each other, and every number counts the bulbs beside its wall. Also known as Akari, Lights, Bijutsukan.
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.
Playing Light Up on Puzzle Solvers
- Choose classic numbering or every wall numbered (easier), a size and a difficulty, then press New Puzzle.
- Tap a square to place a bulb, tap again to mark it bulb-free, a third time to clear. Or pick the Bulb or No bulb tool; drag to mark many.
- The light spreads as you place bulbs; clashing bulbs turn red and numbers turn green when right.
- Hint places one bulb or mark and explains why.
Using the Light Up 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.
A worked example
A 3 sits on the top edge. It has only three neighbours — left, right and below — so all three get bulbs.
Those bulbs light rows and columns, which leaves a dark corner square with just one unlit square beside it that can see it. That square gets the next bulb.
Strategies
- 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.
- Blocked squares. If a bulb on a square would leave another square with no way to be lit, that square cannot hold a bulb.
Common mistakes
- Placing two bulbs in the same row with no wall between them.
- Counting diagonal neighbours for a number — only across and down count.
- Forgetting that an unnumbered wall still blocks light.
Where it comes from
Light Up was published by the Japanese puzzle company Nikoli as Akari (‘light’) in 2001 and is a favourite in puzzle collections as Light Up.
Frequently asked 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.
Keep going
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- Light Up Solverstep by step, every move explained
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