How to play Lanterns

Lanterns is a puzzle about light. Each lantern floods its row and column until a wall stops it, and the whole grid has to be lit — without any lantern shining on another.

The rules

• The grid has white cells and black walls. Lanterns go in white cells only.
• A lantern lights its own cell and every white cell in its row and column, up to the nearest wall or the edge of the grid.
• Every white cell must be lit.
• No lantern may be lit by another: two lanterns never share a row or column without a wall between them.
• A wall with a number has exactly that many lanterns beside it — above, below, left and right, not diagonally. Walls without a number can have any number of lanterns around them.

Every puzzle has exactly one solution, and you can always reach it by reasoning, without guessing.

Your first moves

Start with the numbers. A number with exactly as many open cells beside it as lanterns it needs has no choice at all.

Every lantern you place lights up a cross of cells, and none of them can hold another lantern.

Then look for a dark cell with only one way left to be lit. Its own cell and the cells it can see along its row and column are the only places a lantern could light it from.

The strategy guide covers the reasoning that takes you further.

Playing on this site

• Tap a white cell once for a lantern, and again for a dot — your note that no lantern goes there. A third tap clears it.
• Long-press (or right-click) goes the other way round: dot first.
• Drag across open cells to dot them all at once, or across dots to clear them.
• Lit cells are shaded, so you can see at a glance what is still dark. A number fades once it has all its lanterns.
• Lanterns that light each other, and numbers with too many lanterns, are marked in red straight away. Check shows any lantern or dot that disagrees with the solution, but only when you ask.
• Hint names the next deduction and outlines the cells it settles. One hint per puzzle is free; after that there's a one-minute wait between hints.

Keyboard

• Arrow keys move; L places a lantern, X a dot, 0 clears; Space cycles.
• Z undoes, Y redoes, H asks for a hint.

Sizes and the daily puzzle

• Easy: 7×7.
• Medium: 9×9.
• Hard: 10×10.

Each day's first puzzle is the same for everyone, and they follow the week from Monday's gentlest to Saturday's toughest, with Sunday the next toughest. After it, Next puzzle gives you as many more as you like.