Light Up (Akari) — The Illumination Experiment

Light Up is a grid-based logic puzzle created by Nikoli. You get a grid of open cells and black walls, some of which carry a number from 0 to 4. You place light bulbs in open cells. Each bulb illuminates its own cell plus every cell it can see horizontally and vertically, stopping at walls or the grid edge. The goal: light every open cell while ensuring no two bulbs can see each other. If you have played it in Simon Tatham’s puzzle collection, this is the same light up logic puzzle with a full interface around it.

The akari puzzle (あかり, Japanese for “light”) goes by both names. It pairs line-of-sight illumination with numbered wall constraints, so the reasoning feels different from number-placement or region-filling games. You are not filling in digits or shading cells. You are managing visibility across an entire grid.

Not to be confused with light-up jigsaw puzzles or 3D illuminated products. This is a logic puzzle — the “light” is a mechanic, not a physical feature.

Play the akari game online alongside Sudoku, KenKen, Nonogram, and Star Battle in the grid puzzle collection. We have 1,500 puzzles across five difficulty levels, printable puzzles for offline solving, and a rotating daily Light Up puzzle.

Three rules govern every Light Up puzzle:

1. Illumination. Each bulb lights its cell and all cells in its row and column until a wall or grid edge blocks the light. Every open cell must be lit by at least one bulb.
2. No mutual visibility. Two bulbs cannot share a row or column unless a wall stands between them. If they can see each other, the placement is invalid.
3. Numbered walls. A wall with a number (0–4) tells you exactly how many bulbs must sit in the orthogonally adjacent cells. Unnumbered walls impose no special constraint.

Click or tap to place bulbs. Right-click or tap again to mark cells. Light rays appear in real time as you build your solution. For the complete rules with a worked example, see the rules page.