Light Up is also called Akari. That is its Japanese name, from the puzzle maker Nikoli.
The rules
- A lamp lights its own square. It also shines straight along its row and column.
- The light stops at a black block or at the edge of the board.
- A lamp never shines diagonally.
- Every wooden square must be lit by at least 1 lamp.
- Lamps may never shine on each other. Two lamps can share a row or column only if a black block stands between them.
- A number on a block says how many lamps sit right next to it: above, below, left or right.
- A block without a number can have any number of lamps next to it.
These are the classic Akari rules. Puzzles in books are often bigger than the boards in Quirk.
A worked example
Here is a 4 × 4 board. Boxes with a number are black blocks with that number. "Block" is a black block without a number. Empty boxes are wooden squares.
| Column 1 | Column 2 | Column 3 | Column 4 | |
|---|---|---|---|---|
| Row 1 | 0 | |||
| Row 2 | 1 | |||
| Row 3 | Block | |||
| Row 4 |
- The 0 in row 1, column 4 wants no lamps next to it. So mark row 1, column 3 and row 2, column 4 as No lamp.
- Look at row 2, column 3. The 1 is to its left and a block is below it.
- Only row 1, column 3 and row 2, column 4 could light it from outside. Both are marked No lamp. So this square gets a lamp itself.
- That lamp sits right next to the 1. The 1 now has its lamp. Mark its other sides No lamp: row 1, column 2, row 2, column 1 and row 3, column 2.
- Row 1, column 2 is still dark. It cannot hold a lamp, and neither can row 1, column 3. Only row 1, column 1 can still light it, so put a lamp there.
- That lamp shines down column 1. Row 3, column 1 and row 4, column 1 are now lit, so they cannot hold a lamp.
- Row 3, column 2 is still dark. The 1 is above it and a block is to its right. It cannot hold a lamp, and the square to its left is lit. Only row 4, column 2 can light it, so put a lamp there.
- That lamp shines along row 4. Row 4, columns 3 and 4 are now lit, so they cannot hold a lamp.
- Row 3, column 4 is still dark. A block is to its left. Above it is No lamp and below it is a lit square. So it gets a lamp itself.
- Now there are 4 lamps. Every wooden square is lit, and no two lamps shine on each other.
Beginner techniques
Start with the numbers
A 0 means every square next to it is No lamp. A 4 means all 4 sides get a lamp.
A number can also need every side that is left. A 3 at the edge of the board has only 3 sides. All 3 get a lamp. A 2 in a corner works the same way.
A full number needs no more
Once a number has all its lamps, mark its other sides No lamp. This often starts a chain of easy moves.
Lit squares cannot hold a lamp
After you place a lamp, follow its light along the row and the column. None of those squares can hold another lamp. Mark them in your head or with No lamp.
Find the dark square with one way to be lit
Pick a dark square. Look along its row and column up to the blocks. If only 1 square there can still hold a lamp, put the lamp in that square.
Check both lamp spots
Say a 1 needs a lamp below it or to its left. Find a square that both lamps would light. That square cannot hold a lamp, whichever spot is right.
Common mistakes
- Thinking a lamp shines diagonally. It only shines along its row and column.
- Forgetting that a block stops the light. Two lamps in one row are fine with a block between them.
- Treating a block without a number like a 0. It can have any number of lamps next to it.
- Lighting every square but leaving two lamps that shine on each other.
- Counting a lamp at a corner of a number. Only lamps above, below, left or right count.
Questions
Is Light Up the same as Akari?
Yes. Akari is the Japanese name and Light Up is the usual English name. The rules are the same.
Can two lamps be in the same row?
Yes, if a black block stands between them. The block stops the light, so they do not shine on each other.
Does every puzzle have one answer?
Yes. Each Light Up puzzle in Quirk has exactly one right way to place the lamps.
What sizes are there in Quirk?
The boards go from 4 × 4 up to 8 × 8. Harder puzzles need longer chains of steps, not just more squares.
Is it good for beginners?
Yes. There are only a few rules, and the first boards are small. The numbers give you a clear place to start.
What can I do when I am stuck?
Ask for a hint. It shows a square and explains why a lamp fits there or not. You can also undo moves or reset the puzzle.
Related puzzles
Playing it in Quirk
Tap a square for a lamp. Tap again to mark it No lamp, and once more to clear it.
Drag across squares to mark them all No lamp. A drag gives every square the mark the first square gets. Lamps go one at a time.
