- ➊ Place light bulbs in some of the white cells so that all
white cells are lit and no light bulb is lit by an other light bulb.
- ➋ A light bulb shines horizontally and vertically up to the
next black cell or the edge of the diagram.
- ➌ A number in a black cell indicates how many light bulbs
must be placed in
orthogonally adjacent cells.