Play LITS Online

Four marked rooms, four tetrominoes. LITS asks you to shade a connected shape of four squares inside each room. The shapes must join into one black area, yet a solid two by two block is forbidden. The name comes from the four allowed shapes: L, I, T and S. Start by looking for shapes that can touch a neighboring room without forming a square block.

1. Identify the four three by three rooms divided by thick lines.
2. Click a cell to shade it, click again to mark white and click again to return to unknown.
3. Build one four-square L, I, T or S in every room.
4. Connect the shaded shapes across room boundaries into a single area.
5. Avoid every all-black two by two square.
6. When two shapes share an edge across rooms, make sure they have different letter shapes; mark remaining cells white.
7. Use the thick borders to separate the four rooms. Each contains nine positions and needs one four-cell piece, so five cells per room eventually stay white. Before shading, sketch a few possible L, I, T and S placements within a room. A proposed shape that cannot reach another room is a poor choice even when it fits locally.
8. The letters describe shapes, not colors or specific orientations. When you test a placement in one room, count its four black squares and locate any edge where it can meet the next room. Use those edge contacts to build a connected chain through all four rooms. If a neighboring piece must match the same letter, make sure their cells do not touch.

• Each room contains exactly four black squares forming a legal tetromino.
• Every black square belongs to the same connected black region.
• No two by two block may be completely black.
• Equal tetromino types may not share an edge across a room boundary. Rotations and reflections count as the same type.
• Piece identity ignores rotation and reflection. An L turned upside down still counts as L, and the two forms of an S share a name. Equal shapes are allowed in different rooms only when their black cells do not touch across the border. Also examine every two by two group of squares, including groups straddling thick lines.

• Begin with a room's possible tetromino placements rather than individual black squares.
• Reserve a boundary contact so the black region can reach adjacent rooms.
• A four-square O is never allowed, and any filled two by two square fails the puzzle.
• If two touching rooms both must make an L, move one shape so the L cells do not touch.
• Use white marks to rule out shapes that would isolate the final room.

• Pentomino Fill: Compare how a related puzzle uses regions, paths or tile placement.
• Norinori: Compare how a related puzzle uses regions, paths or tile placement.
• Heyawake: Compare how a related puzzle uses regions, paths or tile placement.

• Recognizing tetromino silhouettes gives a different solving rhythm from number puzzles.
• Boundary contacts force decisions across entire rooms.
• LITS changes how you think about an empty cell. It belongs to a possible four-square piece, rather than merely switching black or white in isolation. A useful placement satisfies its own room, offers a connection outside and avoids a repeated shape next door. That combination creates a compact puzzle with genuinely different deductions from binary grids.

Play Lits free in your browser. Start the interactive board above, use its on-screen controls and check the rules below when a deduction gets stuck. No download or account is needed.

Try another round of Lits on the board above. Start with the most constrained part of the grid, test each move against the stated rules, and use the reset control to try a new approach.

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