Light Up
Puzzle · 2 playsLight Up
Place light bulbs until every white cell is lit — but no bulb may shine on another.
About Light Up
A bright little logic puzzle from Japan, where it goes by the name Akari. Place bulbs on the white cells: each one lights its own square and shines along its row and column until a wall stops it. Every white cell must end up lit, no two bulbs may shine on each other, and a numbered wall needs exactly that many bulbs touching its sides. Every puzzle is freshly generated with exactly one solution, on a 7×7 Easy, 10×10 Medium or 12×12 Hard grid. Tap once for a bulb and again for a cross to mark a cell that stays dark, and lean on a hint if you are truly stuck — each one adds 20 seconds to the clock. Faster solves score more, and your best time for each size is kept. Free to play in your browser — no download, no sign-up.
How to Play
Tap a white cell for a bulb, again for a cross, once more to clear. Right-click or ✕ Mark mode places crosses directly. A bulb lights its row and column until a wall blocks it. No two bulbs may light each other. A numbered wall must touch exactly that many bulbs — above, below, left and right. Light every white cell to solve. Hints add 20 seconds; faster solves score more.
Tips & Strategy
Start with the numbers that leave no choice. A 4 needs a bulb on all four sides, so place them at once. A 0 means none of its neighbours can hold a bulb, so mark every one of them with a cross. A 3 against the edge of the board or beside another wall, or a 2 tucked into a corner, often has exactly as many open neighbours as its number — fill them all. Each placement lights up whole rows and columns, which rules out more cells, so the opening moves tend to cascade.
Use crosses generously. A cross is just a note that no bulb goes there, and it is the best way to keep track of what you have ruled out: every cell lit by a bulb, every cell beside a satisfied number, and every cell beside a 0. Then look for the white cells that are still dark. If only one cell anywhere can light a given dark square — itself or one other spot along its row or column — a bulb must go there.
When it gets tight, check the numbers against their neighbours. A number that has some bulbs already only needs the rest from its remaining open sides; when the count of open sides equals what it still needs, they all take bulbs. Clashing bulbs turn red, and numbers turn red when they have too many, so mistakes show up right away. A hint fixes a mistake or reveals a bulb, but each one adds 20 seconds, and faster solves score more.