Light Up is a logic puzzle about lighting a room full of walls. The grid has black wall cells, some of them carrying a number, and white cells that must all end up lit. You place bulbs on white cells; each bulb shines along its row and column until it meets a wall. Every puzzle here is generated fresh and checked by a solver so that it has exactly one answer.
How to play
The rules.
- Every white cell must be lit by at least one bulb.
- A bulb lights its whole row and column until a wall blocks the light. Two bulbs may not shine on each other.
- A wall with a number has exactly that many bulbs in the cells directly above, below, left and right of it. A wall without a number can have any number.
Placing bulbs. Tap a white cell to cycle through three states: a bulb, a dot (meaning “no bulb here”), and empty again. You can also select a cell and use the 💡 Bulb and · No bulb buttons, or Erase. On a keyboard, B or * places a bulb, the full stop places a dot, and Backspace clears; the arrow keys move between cells. Lit cells turn yellow as you play, so you can see the dark corners that still need light.
Dots are only notes for yourself. The puzzle counts as solved the moment every bulb is in the right place, whether or not the other cells are dotted.
Mistakes and help. Two bulbs that see each other are outlined in red, and so are the bulbs around a wall that already has too many. Hint fixes a wrong bulb if you have one, otherwise it places one correct bulb. Undo takes back your last change. The timer and the number of hints you used appear when you finish.
Difficulty. Choose under Difficulty at the top; New puzzle creates another grid at that size.
| Level | Grid | Numbered walls |
|---|---|---|
| Easy | 7 × 7 | most walls numbered |
| Medium | 10 × 10 | about a third numbered |
| Hard | 14 × 14 | only the numbers needed for a unique answer |
Strategy
Start with the numbers. A 4 means bulbs on all four sides. A 0 means none, so dot every neighbour. A 3 in a corner of the grid or beside another wall often has exactly three free neighbours, which forces all of them.
Count the free neighbours. When a numbered wall has as many empty neighbours as bulbs still missing, every one of them is a bulb. When the number is already reached, dot the rest.
Look for lonely cells. A white cell that sees only walls, or that is boxed in by dots, has to hold its own bulb.
Dot the lit cells. Once a cell is lit, a bulb there would shine on the bulb that lit it. Marking lit cells with dots keeps you from placing an illegal bulb later.
Finish the dark corridors. A short unlit stretch between two walls can only be lit from inside itself. Check which of its cells can still take a bulb without clashing.
If you enjoy Light Up, try Mahjong Solitaire or Math Cages next.
