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Learn Crownlight

Six ways of thinking that light up any castle. Start with the pillars — they decide themselves — then chase the dark rooms.

How to play CrownlightA one-minute video walkthrough is on its way.

  1. Only one cell can light it
  2. "0" means mark them all
  3. "4" means light all four
  4. "3" on an edge, "2" in a corner
  5. Torches can't see each other
  6. The last dark room
  7. Count a satisfied pillar
  8. Count a hungry pillar

1. Only one cell can light it

A dark room with a single cell that could light it gives that cell its torch. Scan every dark room.

Every dark room needs a torch somewhere that can reach it. Most rooms have several candidates — a stretch of row one way, a stretch of column the other. But sometimes, when pillars crowd in, there is exactly one cell whose light can reach a dark room. That cell holds a torch. No guessing, no maybe: if it didn’t, the room would stay dark forever.

Make this a habit: after every torch you place, scan for dark rooms and count their candidates. The rooms with one candidate are free torches. On bigger boards the endgame is often a chain of these — each torch lights new rooms, which narrows the candidates for the rooms still dark.

2. "0" means mark them all

A "0" pillar wants no torches beside it — mark every neighbor X on sight and move on.

A "0" pillar is the simplest thing on the board: it wants no torches touching it, so every white neighbor gets an X the moment you see it. Don’t think, just mark. Those X’s matter — each one is a cell you never have to consider again, and they often trigger the only-lighter rule in neighboring rows.

Zeroes are also information about the dark. A room next to a "0" can only be lit from along its row or column, never from the pillar’s side. When you’re stuck, look at what the zeroes rule out rather than what the other numbers demand.

3. "4" means light all four

A "4" pillar needs a torch on every side. Place all four; they never conflict with each other.

A "4" pillar is surrounded on all four sides by white cells, and it wants a torch on every one of them. Place all four without hesitation — and notice the lovely consequence: those four torches can never see each other (the pillar stands between each pair), so there’s no conflict to worry about.

Four torches at once is the biggest single swing in the game. Each one lights its whole row and column, which usually lights half the board and marks a dozen X’s along the sight lines. When a "4" appears, play it first and let the fallout do your scanning for you.

4. "3" on an edge, "2" in a corner

A "3" on the edge with three open neighbors, or a "2" in a corner with two, has no choice — fill them all.

Pillars on the edge and in corners have fewer neighbors, which makes their numbers brutally decisive. A "3" sitting on an edge (not in a corner) has exactly three white neighbors — all three hold torches. A "2" tucked in a corner has exactly two — both hold torches. Learn to spot these shapes the way you spot a "0": instant, no counting.

The same thinking extends: any numbered pillar whose open neighbors exactly equal the torches it still needs is decided, wherever it sits. Count need, count placed, count open. When need minus placed equals open, fill them all.

5. Torches can't see each other

Every cell a torch lights is a cell that can never hold a torch. Mark the whole sight line X.

Two torches may never shine on each other. That means every cell a torch lights — its whole row and column until a pillar — is a cell that can never hold a torch. Mark the entire sight line X. This is the rule that turns one placed torch into a dozen decided cells.

It also works in reverse as a weapon: if putting a torch on a cell would shine on an existing torch, that cell is X. When you’re weighing a candidate, trace its sight lines first. A surprising number of "maybe" cells die the moment you look down their row.

6. The last dark room

Endgame: one dark room left means exactly one cell can light it. Find that cell, place the torch, done.

The endgame has its own rhythm. When one dark room remains, stop scanning the whole board: exactly one cell can light it, because if two could, you’d have found the deduction earlier. Find the room, trace its row and column, and the single unmarked candidate is your torch.

If the last dark room seems to have no candidates at all, something earlier is wrong — a torch is shining where it shouldn’t, or an X sits on a cell the solution needs. That’s the moment for the Check button, not for guessing.

7. Count a satisfied pillar

A numbered pillar with all its torches placed marks the rest of its neighbors X.

A numbered pillar that already has all its torches is done giving — every other neighbor gets an X. It’s the quiet counterpart to the "0": not "no torches" but "no more torches." Make it automatic: the moment a pillar’s count is met, mark the rest.

Satisfied pillars are also anchors for the only-lighter rule. Their X’d neighbors narrow the candidate sets of nearby dark rooms, which is often what finally isolates a single candidate two rows away.

8. Count a hungry pillar

A pillar that still needs torches with only just enough open neighbors forces every one of them.

When a pillar still needs torches and only just enough open neighbors remain, every one of those neighbors holds a torch. It’s simple subtraction — need minus placed equals open — but it’s easy to miss mid-game when you’re focused on the lighting. Count pillars the way you count dark rooms: routinely.

Forced torches are the most conflict-prone placements in the game, because you place several at once around one pillar. After placing them, immediately check their sight lines against each other and mark the X’s. The pillar guarantees they’re all correct; the sight lines tell you what else that decides.

Try them out: play Crownlight. Watch the sight lines: every torch you place marks a whole row and column of X’s.