Light Up — free browser game
Place light bulbs; illuminate every cell, let no bulb see another, and find the single layout that satisfies the numbered walls.
Controls
Click/tap: cycle a cell (empty → bulb → mark → empty) · Right-click or Shift+click: cycle in reverse · R: reset the level · N: next level
How to play
Tips and detailed strategy
Light Up is a puzzle in which you light every white cell by placing bulbs on a grid divided by dark cells (walls). Each bulb casts light along its own row and column until it hits a wall; to drop a bulb on a cell, click (or tap) it — click again and the cell becomes a 'mark' (×) (this is just your own note and doesn't affect the light), and a third click clears the cell completely. Right-click or Shift+click cycles in the reverse direction. Three rules must hold at once: (1) every white cell must be lit by at least one bulb, (2) no two bulbs may see each other along the same row or column (there must be a wall between them), and (3) the number of bulbs orthogonally adjacent to a numbered wall must exactly equal that number — for example, a wall labelled 2 must have exactly 2 bulbs around it, while a wall labelled 0 wants no bulbs at all. Conflicting bulbs are marked with a red frame and violated numbered walls with a red number. R resets the level and N skips to the next one. The levels build up to ever more intricate patterns; your progress is saved in your browser.