Summary: Akari — also called Light Up — is a logic puzzle on a grid of white cells and black walls. You place lamps on white cells so every white cell is lit. A lamp shines along its row and its column until a wall stops it. Two lamps must not see each other. A numbered wall needs exactly that many lamps in the cells that share an edge with it.
Overview
The board is black walls and empty white squares. Some walls show a number. You place the lamps. The starting grid shows only walls and numbers.
The left-hand grid is the puzzle. The right-hand grid is the same board after every lamp is placed. That pair is a picture of the finished job, not the board to solve first. The numbered 5×5 below is the one to work.
The Goal
Place lamps on white cells so every white cell is lit, no two lamps shine on each other, and every numbered wall has exactly the count it asks for. A well-formed Akari has one arrangement that does all three.
The Rules
- A lamp sits on a white cell. Walls never take a lamp. A lamp lights its own cell.
- Light travels in a straight row or column until a wall. It does not turn a corner and it does not go through a wall. It does not travel on a diagonal.
- Every white cell must be lit. A cell is lit when a lamp sits on it, or when a lamp can see it along that open row or column.
- Two lamps must not see each other. If they share a row or a column and no wall stands between them, both are wrong. A wall between them is enough: two lamps may sit in the same row or column if a wall breaks the run. A white cell a lamp can already see cannot take a second lamp.
- A numbered wall counts the cells that share an edge with it. Up, down, left, right — never the corners. On an interior wall that is four cells; on an edge it is three; in a corner it is two. The number is how many of those neighbours hold a lamp. The digit can be 0, 1, 2, 3, or 4. A 0 means none of those neighbours gets a lamp.
- A blank wall is still a wall. It blocks light. It does not ask for a count.
- One legal arrangement. Every Puzzle Maker Pro Akari is kept only when exactly one lamp layout satisfies the rules.
How to Play
Work the left-hand 5×5. Rows and columns are numbered 1–5. Fold or cover the right-hand grid so only the left board is visible. Pencil a small dot in every cell you have proved cannot hold a lamp — you will need those dots on the last move.
- Start with the 4. The 4 at row 4, column 2 is interior, so it has four white neighbours and needs a lamp in every one. Place lamps at row 4 column 1, row 3 column 2, row 4 column 3, and row 5 column 2. Those four lamps do not see each other: the 4 itself sits between the pair on its row and between the pair on its column.
- Update the light. Column 1, column 3, row 3, and row 5 are now fully lit. Dot the empty white cells on those lines — a second lamp there would see one you just placed. Start with row 1 column 1, row 3 column 4, and row 5 column 4. The blank wall at row 2 column 2 stops the lamp at row 3 column 2, so row 1 column 2 stays dark.
- Read the 0. The 0 at row 2, column 4 forbids a lamp in each neighbour that exists: row 1 column 4, row 2 column 3, row 2 column 5, and row 3 column 4. Dot those four. A 0 forbids a lamp in those neighbours; the cells must still be lit from another row or column. Row 2 column 3 and row 3 column 4 are already lit from step 2. Row 1 column 4 and row 2 column 5 still need light from further along their line.
- Finish the 2. The 2 at row 4, column 4 already has one lamp (row 4 column 3). Its up and down neighbours (row 3 column 4 and row 5 column 4) are already lit, so they cannot take a lamp. Only row 4 column 5 can still hold a lamp. Place it.
- See what that lamp covers. Column 5 has no wall, so the new lamp lights the whole column — including row 1 column 5 and row 2 column 5. Look back at row 1: which cells are still dark?
- Light the last dark cells. Two white cells still have no lamp that can see them: row 1 column 2 and row 1 column 4. Row 1 has no wall, so a lamp on either would light the other. Row 1 column 4 still has your 0-dot, so it cannot hold a lamp. The only legal seat left on the row is row 1 column 2. Place it. The blank wall at row 2 column 2 sits between this lamp and the lamp at row 3 column 2, so they do not see each other. Along row 1, the new lamp lights the dotted cell at row 1 column 4.
Every white cell is lit. No two lamps see each other. The 4, the 2, and the 0 all match. That is the whole board.
Outcome
You can read a numbered wall as an edge-count, place a 4’s lamps on sight, treat a 0 as forbidden neighbours, and finish a 2 from the neighbours that are still legal. You can also check a finished board: every white cell lit, no two lamps on an open line, every number exact among the cells that share an edge with it. On a larger grid, start the same way: a 3 on an edge has three white neighbours and fills like this 4.
Print another board from the free Akari pack, or try the free demo if you want to make pages like these. The create walkthrough is Getting Started with Akari. More how-tos live on Akari Tutorials. The shop page is Puzzle Maker Pro – Akari (Light Up).
Try It Online
When a Light Up grid is playable online, click a white cell to cycle it: empty, then a lamp, then a mark (no lamp), then empty again. Walls stay locked. An empty cell a lamp can already see may show a warm tint — that tint is a hint, not a new rule; a second lamp there is still illegal, and two lamps that see each other pulse as a conflict. So does a numbered wall that already has too many lamps next to it. A wall that still needs more lamps is not a conflict yet. Play one here: [/puzzles/akari/ – confirm]. For the general controls — verify, reset, the timer, working through a set — see How to Play Puzzles Online.
FAQ
What is Akari, and is it the same as Light Up?
Yes. Akari is the Japanese name; Light Up is the English name. Same grid, same rules.
What are the rules of Akari (Light Up)?
Place lamps on white cells so every white cell is lit. Light runs along a row or column and stops at a wall. Two lamps must not see each other. A numbered wall needs exactly that many lamps in the cells that share an edge with it.
Can two lamps sit in the same row or column?
Yes, when a wall stands between them. They must not share an open run of white cells.
What does a 0 on a wall mean?
None of the cells that share an edge with that wall may hold a lamp. Those cells still have to be lit by a lamp further along their row or column.
Does every Akari puzzle have only one solution?
A well-formed Akari has one lamp arrangement. Puzzle Maker Pro only keeps boards that do.
Do lamps light diagonally?
No. Light runs only along the row and the column, and it stops at a wall. Corner-touching cells do not see each other.
How do I know I have finished?
Every white cell is lit, no two lamps see each other, and every numbered wall has exactly the lamps it asked for among the cells that share an edge with it. If all three hold, you are done.