Light Up
Illuminate the grid with logic
Light Up (known as Akari in Japan) is an illumination logic puzzle where you place light bulbs on a grid so that every white cell is lit. Bulbs shine horizontally and vertically until blocked by a black cell or the grid edge. The twist: no two bulbs can illuminate each other. Numbered black cells tell you exactly how many bulbs must be placed in their orthogonal neighbors. These constraints create elegant deduction chains that make Light Up a favorite among logic puzzle enthusiasts.
How to Play Light Up
Place Bulbs
Place light bulbs on white cells. Each bulb illuminates its entire row and column until blocked by a black cell or grid edge.
Light Everything
Every white cell must be illuminated by at least one bulb. No dark cells allowed in the solution.
No Conflicts
No two bulbs can see each other. If two bulbs are in the same row or column with no black cell between them, that's invalid.
Numbered Clues
Black cells with numbers tell you exactly how many of their 4 orthogonal neighbors must contain bulbs.
Unnumbered Walls
Black cells without numbers can have any number of adjacent bulbs (including zero). They simply block light.
Logical Solution
Every puzzle has one unique solution reachable through deduction. No guessing required.
Strategy & Solving Tips
Skilled Light Up solving means using numbered clues as anchor points and then reasoning about where bulbs must go to avoid conflicts.
- A numbered clue equal to its available neighbors forces all those neighbors to have bulbs
- A "0" clue means none of its orthogonal neighbors can contain a bulb — mark them as empty
- After placing a bulb, mark its entire visible row and column as "lit" — no more bulbs can go there
- Find cells that can only be illuminated by one possible bulb position — that bulb is forced
- Corners with numbered clues are especially constraining since they have at most 2 neighbors
- Work from high-numbered clues (3s and 4s) first, as they have the fewest valid configurations
Common Mistakes to Avoid
- Placing a bulb that illuminates a needed dark area but accidentally shines on another bulb — always check sight lines
- Forgetting that numbered clues count ALL orthogonal neighbors, not just the empty ones you can see
- Ignoring cells that can only be lit by one possible bulb position — these are forced placements
- Not marking cells as "lit" after placing a bulb, leading to redundant bulb placements later
Light Up FAQ
How far does a light bulb shine?
A bulb illuminates every cell in its row and column in both directions, stopping only when it hits a black cell or the edge of the grid. It does not shine diagonally.
Can I place a bulb on a black cell?
No. Bulbs can only be placed on white cells. Black cells act as walls that block light and sometimes provide numerical clues.
What if a numbered clue says 4?
A "4" clue means all four orthogonal neighbors must contain bulbs. This is only possible when the numbered cell is not on an edge or corner, having exactly four white neighbors.
Why does this puzzle have two names?
The puzzle was created by Nikoli (a Japanese puzzle publisher) under the name "Akari." In English-speaking countries, it's commonly called "Light Up" for its illumination theme.
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Ready to Play Light Up?
Light up your logical thinking with Akari — the puzzle where every bulb you place illuminates the path to the solution. Strategic placement, no conflicts, pure satisfaction.