Light Up is a logic puzzle played on a grid of white squares and black walls. You place light bulbs until every white square is lit, following a few simple rules. Every puzzle has exactly one solution, and you can always reach it by reasoning.
The rules
A bulb lights its own square and every square in its row and column, until the light reaches a black wall or the edge of the grid.
Every white square must be lit by at least one bulb.
No bulb may shine on another bulb: two bulbs can only share a row or column if a wall sits between them.
A number on a wall tells you exactly how many bulbs touch it on its four sides. Walls without numbers can have any number of bulbs around them.
Placing bulbs and marks
Tap a white square to place a bulb, and tap it again to remove it. Hold a square to mark it with a dot, which means "no bulb here". Dots are notes for you and don't count toward the solution.
If you prefer to mark more than you place, flip the Bulb / Mark switch under the board: taps then place dots and holding places a bulb. Undo takes back your last change. On a keyboard, use the arrow keys to move, Space to place a bulb and X to place a dot.
Reading the board
Lit squares glow yellow, so dark squares show what is still left to light.
Bulbs that shine on each other turn red.
A numbered wall fades once it has the right number of bulbs, and turns red if it has too many.
The puzzle is solved the moment every square is lit and every rule is met.
Where to start
A 4 needs bulbs on all four sides, so place them straight away.
A 0 means no bulbs around it, so dot every square that touches it.
A 3 against the edge or another wall has only three free sides, so all three get bulbs. The same goes for a 2 in a corner.
Once a number has all its bulbs, dot the rest of its neighbours.
Strategy for harder puzzles
Look for a dark square that only one square can still light, counting itself. That square must hold a bulb.
Dot squares that are already lit: a bulb there would see the bulb lighting it.
Pay attention to how numbers interact: two numbers sharing a corner square often decide which side a bulb goes on.
On Hard, if you get stuck, try a bulb in one spot and follow the consequences. If it leads to a contradiction, undo and dot that square instead.
Difficulty levels
Easy is a 7×7 grid with plenty of numbers. Normal is a 10×10 grid you can solve step by step without guessing. Hard is a 12×12 grid with as few numbers as possible. Every puzzle is freshly made, has exactly one solution, and your best time is kept for each level.