Tap an empty cell to place a bulb. Bulbs emit light in all 4 directions until blocked by a wall.
Bulbs must not shine on each other (no two bulbs in the same row/column without a wall between them).
A number on a wall indicates exactly how many bulbs must be placed in the 4 adjacent cells.
Walls without numbers have no constraint on adjacent bulbs.
1
0
Walls with 0 can't have any adjacent bulbs — mark X on all neighboring cells first.
Walls with 4 require bulbs on all four sides.
Corner and edge number walls have fewer possibilities, making them easier to solve.
Light Up is an NP-complete problem requiring constraint propagation and logical reasoning. Regular practice with constraint satisfaction puzzles has been shown to enhance prefrontal executive functions and reasoning ability.
McPhail, B. (2005). Light Up is NP-complete. Unpublished manuscript.