Only Light Source
An unlit cell with only one cell left that could light it: that cell holds a bulb.
How it works
- 1The corner cell is still dark, and walls cut its row two along and its column two down.
- 2So only three cells in the whole grid could ever light it: itself, and the one beside it in each direction.
- 3Both of those have already been ruled out.
- 4One candidate left, so the bulb stands in the corner itself. This is the technique that finishes most boards once the clues have run dry.
- Cells that establish the pattern
- Bulb this technique places