Step 3 of 8
"4" means light all four
Four neighbors, four torches, no choices anywhere.
The rule of thumb: A "4" pillar needs a torch on every side. Place all four; they never conflict with each other.
A "4" pillar is surrounded by white cells on all four sides, and it wants a torch on every one of them. Place all four without hesitation.
Notice why it’s safe: the pillar itself stands between each pair of those torches, so none of them can ever shine on another. Four torches at once is the biggest single swing in the game — the light they spread, and the X’s along their sight lines, decide a big share of the board. The play page’s boards don’t deal "4"s, but hand-made puzzles love them; these practice boards are built around one. Find it first and let the fallout do your scanning.
Where to look: Any "4", the moment the board opens. A "4" needs four white neighbors, so it never sits on an edge.
Worked example
A real position from a board that needs "4" means light all four. Purple: what the reasoning rests on. Dashed: the cells in question. Green: what it proves.
Now the same trick at the edges of the board, where the numbers shrink but stay just as certain. Step 4: "3" on an edge, "2" in a corner →