Light Up (Akari) Puzzle

What is Light Up (Akari)?

Light Up, known in Japan as Akari, is a single-player logic puzzle played on a square grid of white and black cells. Your job is to place light bulbs into white cells so that every white cell in the grid is illuminated. A bulb lights its own cell and sends a beam along its row and its column in all four directions; the beam keeps travelling until it meets a black wall or the edge of the grid. Because the puzzle is solved purely by deduction — there is no guessing if you reason carefully — it rewards patient, logical thinking and makes a satisfying printable activity for older children, teenagers and adults alike.

Each puzzle this tool produces is built from a fully valid bulb arrangement first, then the bulbs are hidden to create the printed challenge. That means every sheet has a genuine, consistent solution, and the answer key matches it exactly.

The rules of Akari

There are only three rules, and they combine to make a surprisingly deep puzzle. First, every white cell must be lit. A cell is lit if it contains a bulb or if a bulb shines into it along an unobstructed row or column. Second, no bulb may light another bulb — if two bulbs share a row or column with no wall between them, the arrangement is illegal. Third, the numbered black cells act as clues: a number tells you exactly how many bulbs touch that black cell along its four orthogonal edges (up, down, left and right). Black cells without a number can have any quantity of adjacent bulbs, from zero to four.

Walls do two jobs at once. They block beams, which lets bulbs coexist in the same row or column, and the numbered ones pin down precisely how many bulbs hug their sides. Reading those numbers carefully is usually the fastest way into a fresh grid.

How to solve it

Start with the most constrained clues. A black cell marked 4 must have a bulb on every side, so place all four immediately. A cell marked 0 forbids bulbs on all four neighbours, so cross those cells off. Where a clue equals the number of white neighbours it has, every one of those neighbours must hold a bulb. After placing a forced bulb, trace its beams and mark all the cells it lights — those cells can no longer take a bulb, because a second bulb there would be lit by the first.

Next, look for white cells that can only be lit one way. If a lonely white cell has just a single white cell in its row and column reach, a bulb must go in the only square that can reach it. Keep alternating between satisfying the number clues and chasing down dark cells, and the grid resolves itself. If you ever create two bulbs that see each other, you have made a mistake earlier — back up and recheck your forced moves.

Customising your puzzle

• Grid size — pick a 6x6 board for a quick warm-up or step up to 10x10 for a meatier challenge.
• Difficulty — easy boards reveal more clue numbers and use fewer walls; hard boards hide more numbers so you must lean on lighting logic.
• Answer key — include a second page that shows every bulb in place for instant marking.
• Name and date — add classroom fields at the top of the sheet.
• Seed — type a word or number to reproduce the exact same puzzle, or leave it blank for a fresh board each time.

Why Akari is great practice

Akari trains the same constraint-satisfaction muscles as Sudoku and binary puzzles, but with a spatial, beams-and-shadows twist that many solvers find refreshing. It encourages working forwards from certainties rather than guessing, and it gives immediate visual feedback — a dark cell or a clashing pair of bulbs is easy to spot. The puzzles print cleanly in black and white, so they are ideal for classroom starters, indoor break-time activities, screen-free travel entertainment, or gentle daily brain training. Pair them with the answer key and a class can mark their own work in seconds.