Setup and opening position
Black wall cells interrupt lines of sight, and some walls show a number from zero through four. All other cells begin empty and may either hold a bulb or remain unoccupied.
Light Up
Place the unique set of bulbs that lights every open cell while satisfying every numbered wall and line-of-sight rule.
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How to play
Place the unique set of bulbs that lights every open cell while satisfying every numbered wall and line-of-sight rule.
- Black wall cells interrupt lines of sight, and some walls show a number from zero through four. All other cells begin empty and may either hold a bulb or remain unoccupied.
- A bulb illuminates open cells horizontally and vertically until a wall blocks the ray. Bulbs may not see one another, and a numbered wall must touch exactly that many bulbs orthogonally.
- Place the unique set of bulbs that lights every open cell while satisfying every numbered wall and line-of-sight rule.
Strategy tips
- Resolve zero clues and nearly completed numbered walls first, then identify dark cells with only one possible bulb source and reserve that source before filling flexible areas.
- Lighting a square is not enough to justify a bulb there; the bulb must also avoid every visible bulb and preserve the exact counts around nearby numbered walls.
- Scan each row and column segment between walls for darkness and bulb conflicts, then recount the orthogonal neighbors of every numbered wall.
Complete guide
Rules, scoring, and strategy
Light Up is a complete browser implementation with its own versioned rules profile. Place bulbs on a five-by-five wall grid so every open square is lit and no two bulbs shine directly at one another.
Legal moves and game flow
A bulb illuminates open cells horizontally and vertically until a wall blocks the ray. Bulbs may not see one another, and a numbered wall must touch exactly that many bulbs orthogonally.
Winning and terminal positions
Place the unique set of bulbs that lights every open cell while satisfying every numbered wall and line-of-sight rule. Scan each row and column segment between walls for darkness and bulb conflicts, then recount the orthogonal neighbors of every numbered wall.
Practical strategy
Resolve zero clues and nearly completed numbered walls first, then identify dark cells with only one possible bulb source and reserve that source before filling flexible areas. Lighting a square is not enough to justify a bulb there; the bulb must also avoid every visible bulb and preserve the exact counts around nearby numbered walls.
Questions players ask
What is the objective in Light Up?
Place the unique set of bulbs that lights every open cell while satisfying every numbered wall and line-of-sight rule.
Which moves are legal in Light Up?
A bulb illuminates open cells horizontally and vertically until a wall blocks the ray. Bulbs may not see one another, and a numbered wall must touch exactly that many bulbs orthogonally.
What should I plan first in Light Up?
Resolve zero clues and nearly completed numbered walls first, then identify dark cells with only one possible bulb source and reserve that source before filling flexible areas.