Light Up Puzzles
Place bulbs so every square is lit, and no bulb shines on another.
Hints available. Play as many boards as you like.
Ready when you are.
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Scan for the same board — no hints.
How to play
Tap any white square to place or remove a bulb. A bulb lights its whole row and column until a black wall blocks it. The board is solved when every white square is lit.
No bulb may light another bulb. If two bulbs share a row or column with no wall between them, the arrangement is wrong however well lit the board looks.
A number on a wall says exactly how many bulbs touch it on its four sides — not diagonally. A wall with no number tells you nothing and constrains nothing.
Strategy
Start with the extremes. A wall marked 0 forbids a bulb on all four of its sides, and a wall marked 4 requires one on each. Those two numbers place or eliminate squares with no reasoning at all, and they usually cascade.
Then look for squares only one bulb could reach. Scan for a white square whose row and column are boxed in by walls; if only one position can light it, that position must hold a bulb. Corners hemmed in by walls are the usual place to find this.
Late in a board, use the negative form. A wall marked 1 that already touches a bulb forbids bulbs on its three remaining sides — and those eliminations are often what forces the last few squares.
Difficulty and variants
Easy is a 7x7 grid, medium 8x8 and hard 9x9, each with slightly fewer walls than the last. Fewer walls means longer sightlines, which makes the no-mutual-lighting rule far harder to satisfy.
Questions, answered
What is a Light Up puzzle?
A grid of white squares and black walls where you place bulbs until every white square is lit, no bulb shines on another, and every numbered wall touches exactly that many bulbs. It is also known as Akari.
Is Light Up the same as Akari?
Yes. Akari is the original Japanese name; Light Up is the common English one, and the rules are identical.
Can a bulb be placed on a black square?
No. Bulbs only go on white squares. Black squares are walls, and they block light rather than carry it.
Does a wall number count diagonal bulbs?
No. Only the four squares directly above, below, left and right of the wall count toward its number.