Light Up (Akari)
Place light bulbs so every white square is lit.
How to play Light Up
Light Up is a logic puzzle from Japan, where it is called Akari. The board is a grid of white squares and black walls. Some walls show a number. You place light bulbs on the white squares.
Goal
Light up every white square while following these rules:
- A bulb lights its own square and shines in straight lines up, down, left and right until it hits a wall or the edge of the board.
- Every white square must be lit by at least one bulb.
- Two bulbs may never shine on each other. If they are in the same row or column, a wall must stand between them.
- A wall with a number must have exactly that many bulbs next to it, directly above, below, left or right. Walls without a number can have any number of bulbs around them.
Every puzzle here has exactly one answer, checked by a solver before you play.
Step by step
- With the Bulb tool, tap a white square to place a bulb. Its light fills the row and column. Tap again to remove it.
- Switch to the Mark tool to put a small dot on squares that cannot hold a bulb. Dots are only notes. On a computer, right-click uses the other tool.
- With the keyboard, move with the arrow keys and press Space to use the current tool. Press L for a bulb, X for a dot, Backspace to clear and T to switch tools.
- Bulbs that shine on each other turn red. A number turns grey when it has the right count and red when it can no longer be met. Press Undo to go back one step.
Levels
Easy is a 7×7 grid you can solve with the basic rules. Medium is 10×10 and sometimes asks you to test an idea. Hard is 12×12 and shows as few numbers as possible.
End of the game
The puzzle is solved when every white square is lit, no two bulbs see each other and every number is met. The timer stops and the room glows. Your game is saved in this browser. Next, try Hitori.
Strategy tips
- Start with 4s and 0s. A 4 needs bulbs on all four sides. A 0 means none of its neighbours can have a bulb, so mark them with dots.
- Full numbers. If a number has as many free neighbours as its value, every one of them gets a bulb. A 3 against the edge of the board and a 2 in a corner work this way.
- Find lonely squares. A white square boxed in by walls on all sides can only be lit by a bulb on itself.
- Only one way to light it. If a dark square can only be reached from one free square (itself or one in its row or column), that square needs a bulb.
- Mark lit squares near numbers. A square already in the light can never take a bulb. This often finishes the count around a number.
- Look at diagonal pairs. Next to a 3 or a 1, a bulb in one spot can rule out another. Testing a spot and seeing if it breaks a number is a strong move on Hard.
Light Up FAQ
Is Light Up the same as Akari?
Yes. Light Up and Akari are two names for the same puzzle. In Japan it is also called Bijutsukan, which means "art gallery".
Does every puzzle have one answer?
Yes. Every new puzzle is checked by a solver, so there is exactly one way to place the bulbs, and it can be found with logic.
Do walls without numbers matter?
They block light like any wall, but they put no limit on how many bulbs can sit next to them.
What do the dots do?
Dots are notes for squares where a bulb cannot go. They do not affect the answer, but they make it easier to see your options.
