Place light bulbs so every white cell is lit, without two bulbs seeing each other.
Tap an empty white cell to place a bulb. Tap again to remove it.
A bulb lights its own cell, plus every cell extending up, down, left, right until a black wall (or the board edge) stops the light.
Two bulbs may not see each other — i.e. there must be a wall between any two bulbs that share a row or column. Conflicting bulbs glow red.
Clear a level when every white cell is lit and no two bulbs conflict. The next puzzle starts automatically. Six puzzles total, each larger than the last.
Goal: clear all six puzzles in the lowest total time.
Start with cells that have only one legal home for a bulb. A white cell flanked by walls on three sides usually pins down a bulb in the only remaining direction; following those forced moves first chips away at the puzzle without guessing. Long corridors of white cells with no wall between them can hold only one bulb total, so pick the cell that also illuminates a stubborn corner elsewhere.
When you place a bulb, immediately scan its row and column for any second bulb that now sees it — those conflicts (highlighted red) are usually the cheapest mistakes to undo. Dark cells deep in clusters of walls are the trickiest: they tend to need a bulb directly adjacent because the surrounding walls block light from far away. Save such cells for last, then place a single bulb in the only opening they have, and the rest of the board often falls into place.