Place bulbs to light every white square; bulbs never shine on each other and numbers count the bulbs beside them
Akari, also called Light Up, is a logic puzzle about placing light bulbs. The grid has white squares and black squares. A bulb lights its own square and shines along its row and column in all four directions until a black square or the edge stops it. The goal is to light every white square with no bulb shining on another bulb. Some black squares carry a number from 0 to 4: exactly that many bulbs must sit on the squares directly above, below, left and right of it. Every grid here is new and has exactly one solution, which a solver proves before the puzzle appears.
Choose a level: easy is a 7×7 grid with a number on every black square, medium is 9×9 with some numbers removed, hard is 10×10 with as many numbers removed as the puzzle allows while staying unique.
Press New puzzle. Black squares block light; numbered ones tell you how many bulbs touch them.
Tap a white square once to place a bulb, a second time to turn it into a dot (no bulb here), a third time to clear it. Lit squares turn yellow.
On a keyboard, arrow keys move between white squares and skip black ones; Space places or removes a bulb, X places a dot, Backspace clears, Ctrl+Z undoes.
With Show clashes on, a bulb that shines on another bulb is crossed out, and a number with too many bulbs, or too few once all its sides are decided, turns red.
When every white square is lit and every number is right, the puzzle ends and your time is saved as a best for that level.
Deduction from local and long-range constraints together. Numbers give local rules about the four squares around a black square, while light travels across the grid, so each bulb you place rules out squares far away from it. Solving means switching between those two scales, spotting squares that only one remaining bulb position can light, and keeping track of what is forced. It exercises visual scanning along rows and columns, planning ahead and checking consequences before committing.
Start at the 4s and 0s. A 4 has bulbs on all four sides; a 0 has none, so dot all its neighbours.
A 3 against the edge of the grid or beside another black square has only three free sides, so all three take bulbs. The same goes for a 2 in a corner.
Find dark squares that can be lit from only one place. If a white square sits in a short run walled in by black squares, the bulb that lights it may have only one possible spot.
Every square a bulb shines on can never hold a bulb. Mark them with dots to keep track.
Once a number has its full count of bulbs, dot the rest of its sides; once it has as many open sides as bulbs it still needs, fill them all.
An unnumbered black square gives no clue about its neighbours. Only the numbers count bulbs.
Akari, also known as Light Up, is a logic puzzle where you place light bulbs on a grid of white and black squares. Each bulb lights its row and column until a black square, every white square must be lit, bulbs may not light each other, and numbered black squares say how many bulbs touch them.
Yes. Light Up is the English name for the same puzzle; akari is the Japanese word for light.
No. Light travels only up, down, left and right, and it stops at the first black square or the grid edge.
No. A number counts only the four squares that share a side with it: above, below, left and right.
Yes. The generator lights a random layout, numbers every black square, and a solver checks that only one placement of bulbs works. On medium and hard, numbers are then removed one at a time, and a removal is kept only if the solver still finds exactly one answer.
Grid size and clues: easy is 7×7 with every black square numbered, medium is 9×9 with some numbers removed, hard is 10×10 with as many numbers removed as possible while keeping a single answer.
It is free with no sign-up. Your best time per level, the number of puzzles you have solved and the Show clashes setting are saved in this browser only.