Light Up 美術館

Light Up, also known as Akari, is a Nikoli logic puzzle played on a grid of white and black cells. You place light bulbs on white cells. A bulb shines along its row and its column until the light reaches a black cell or the edge of the grid, and the goal is to light every white cell. Two bulbs may never shine on each other, and a number on a black cell tells you exactly how many bulbs sit in the cells directly beside it.

Nikoli developed the puzzle in 2001 under the name 美術館 (Bijutsukan, meaning art gallery). Akari is the Japanese word for light and the name Nikoli uses in English; Light Up is the name most puzzle sites use. The rules take a minute to learn, but the interplay between numbers, walls and beams of light produces deductions that reach right across the grid.

LogicPuzzles.io serves a new daily 7×7 Light Up puzzle that everyone receives on the same day, plus unlimited 5×5, 7×7 and 10×10 puzzles. Every grid is generated with exactly one solution, verified by an exact solver, and kept only if it can be finished by deduction alone. Bulbs, × marks, undo, a timer and the Check button run in the browser, and your progress is saved on your device.

Begin with the numbers that leave no choice. A black cell in a corner touches only two white cells and one on an edge touches three, so a 2 in a corner, a 3 on an edge and a 4 anywhere are all forced: every free neighbour gets a bulb. A 0 tells you the opposite. Mark each of its neighbours with × so you never place a bulb there by accident.

Every bulb lights a line of cells, and none of those cells can hold another bulb. Mark them with × to see which dark cells have only one way left to be lit. A dark cell with a single candidate, itself or one cell along its row or column, forces a bulb there. A white cell boxed in on all four sides by black cells or the frame is the simplest case: only its own bulb can light it.

Numbers also work by subtraction. Once a 1 has a bulb beside it, its other neighbours get × marks. If a 1 has exactly two free neighbours and both also touch a diagonally adjacent 1, one bulb goes into those two cells, so the second 1 is satisfied and its other neighbours are empty. Then look ahead: if a bulb in some cell would leave another dark cell with no way to be lit, that cell gets an ×.

The most common mistakes are counting diagonal bulbs toward a number, forgetting that an unnumbered black cell accepts any number of bulbs, and assuming light continues past a black cell. When you are stuck, press Check: it highlights bulbs that shine on each other, numbers with too many bulbs and bulbs that do not belong to the unique solution.

Nikoli developed Akari in 2001 and published it in Japan as 美術館 (Bijutsukan, art gallery), a name that suggests lamps placed so that every part of a gallery is lit. Outside Japan the puzzle is usually published as Light Up or Akari. In 2005 Brandon McPhail showed that deciding whether a Light Up grid can be solved is NP-complete, which is why large grids are built with care to keep a single solution that logic alone can reach. Nikoli’s own rules text remains the reference: light bulbs go in white squares, every white square must be illuminated, a bulb may not illuminate another bulb, and a number shows how many bulbs are next to it vertically and horizontally.