Light Up
A quiet corner. A bright idea.
Bring every square to light.
Place bulbs on white squares. Match the numbered walls, and keep bulbs out of each other’s sight.
Tap a white square to place or remove a bulb.
Scroll inside the board ↔ ↕ to reach every square. Whole-board view shows the entire puzzle without changing it.
Overview only. Return to tap view to place bulbs or marks.
A little brighter, everywhere.
Every white square is lit. Bulbs do not see each other, and every numbered wall has exactly the right neighbours.
Choose a little light
Easy, Tricky and Hard are the original generator settings, not human-calibrated difficulty ratings.
Every square has its moment
- Put bulbs on white squares. A bulb lights its own square and every white square in its row and column, until a black wall blocks the light.
- Light every white square. Two bulbs must never see each other in the same uninterrupted row or column.
- A number on a black wall is the exact number of bulbs directly next to it: above, below, left and right. Diagonals do not count. A 0 must have no adjacent bulbs.
- Unnumbered black walls only block light. Use × marks to remember where you think a bulb cannot go. Marks can be lit, and they do not change the rules.
Choose Bulb, Mark or Clear, then tap a white square. Tapping again with the same Bulb or Mark tool removes it. A red ! marks mutually visible bulbs, too many neighbours, or a number that cannot be met without removing a mark. A ✓ only means that wall’s number matches, not that the puzzle is solved. A move without a warning is not guaranteed correct.
On small screens, scroll inside the board for 44 px targets. Whole-board view is read-only. Keyboard: Tab to a white square, Enter or Space to use the selected tool, arrow keys to move to the next white square in that direction. B places or removes a bulb, M places or removes a mark, and Delete clears the focused square. Escape closes this help or the puzzle picker.
Undo reverses a move. The last 200 moves are kept. Restart asks first and clears the attempt, but keeps its completed mark and best result. Completion is always rechecked on the current board; an old completed mark never makes an incorrect board win.
If browser storage fails, you can choose “Play in this tab only”. This keeps your current bulbs, marks, Undo history and best result in a temporary session, without replacing the browser’s saved version. It does not resolve a conflict in another tab. The temporary session never reconnects or copies itself into browser storage; closing or refreshing loses it.