This light up puzzle, also called akari, runs on our own engine. The generator scatters black squares, places a random set of lights that lights everything, writes the numbers, and then removes numbers as long as the solver still finds exactly one answer. Our tests compare the solver with a brute-force count of every possible set of lights on hundreds of small grids.
Rules
- Place lights in white squares.
- A light shines along its row and column in all four directions, until a black square or the edge stops it.
- Every white square must be lit.
- No light may stand where another light shines on it.
- A number on a black square says how many lights touch its four sides. Black squares without a number can have any count.
Tap a white square for a light, again for a dot (no light), and once more to clear it. Lit squares turn yellow as you play. Two lights that see each other turn red, and a number turns gray once it has its lights, or red when it can no longer get them.
Levels
Easy grids are 7 by 7 and medium grids 10 by 10; both can be finished with the basic rules alone. Hard grids are 10 by 10 and also need trial steps: suppose a light stands in a square, follow the rules, and see whether some square can no longer be lit.
Strategy
- Fours and corners: a 4 has lights on all four sides; a 3 against the edge and a 2 in a corner have no choice either.
- Zeros: dot every square beside a 0.
- Lonely squares: a white square that no other square can see must hold a light itself.
- Last source: when only one free square can still light some square, the light goes there.
- After each light, dot everything it shines on; the board narrows down quickly.
Hints and statistics
Hint shows the next step the engine can explain, from number counts to the last source for a dark square, or a trial step on hard grids. Check and Show mistakes mark lights or dots that disagree with the answer. Your times and daily streak are stored per level in this browser. Other shading puzzles: nurikabe, star battle and heyawake.
Solver tested . Found a problem? Tell us.
Questions
Is light up the same as akari?
Yes. Akari is the Japanese name and light up the usual English one. The rules are the same.
Do lights shine diagonally?
No. A light shines only along its row and column, and a black square blocks it.
Does a numbered black square count diagonal lights?
No. Only the four squares that share a side with it count.
Is the daily light up puzzle the same for everyone?
Yes. Our generator builds it from the date, one grid per level, and it changes at midnight on your device.