dankpuzzles

light every square, lamp by lamp

Lampblack, the lamps puzzle

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– Tap a square for a lamp, again for a dot. Light every square; lamps never see each other.

Loading today’s lamps puzzle…

Keyboard: arrows move, Space cycles lamp → dot → empty, Ctrl+Z undoes.

Lampblack is the dankpuzzles lamps puzzle. Lampblack is the soot from oil lamps that printers ground into their ink for centuries, so the name ties the lamps on the board to the ink of a type case. A new board every midnight UTC, the same for everyone: 7 by 7 on Monday and Tuesday, 8 by 8 on Wednesday and Thursday, 9 by 9 on Friday and Saturday, and on Sunday the week’s hardest 9 by 9.

Stars: ★★★ for a solve without Hint or Check, ★★ with either. Hint shows the next step the site’s solver would take, with its reason in one sentence; Check says how many of your lamps and dots are wrong, not which, and refuses a board with a clash. Undo and Restart are free. Two lamps that shine on each other, and a wall with too many lamps, turn red at once; a numbered wall with exactly its lamps fades. Your progress stays in this browser only.

Want something else? Today’s Typeslide is a sliding grid of letter tiles, the word ladder changes one letter at a time, the nonogram draws a picture from numbers, Quoin splits a grid into boxes and Ligature joins islands with lines. Or stay with lamps: More lamps makes practice boards in the size and level you pick.

We count visits and plays anonymously. No cookies, no personal data.

What we count

Each visit adds one to a count for the page’s address, nothing more. The lamps puzzle adds six tallies, and today’s puzzles two more, each a fixed name with no puzzle number, no cookie and nothing about you or your board. One tally goes up by one when:

  • lamp-start you place your first lamp or dot on today’s puzzle (once a day per browser)
  • lamp-solve you finish today’s lamps puzzle (once a day per browser)
  • lamp-share you tap Share result after solving today’s puzzle
  • lamp-arrive you open the page from a shared result’s link (once per link per browser)
  • lamp-archive-solve you solve a past puzzle for the first time (once per puzzle per browser)
  • lamp-quick-solve you solve a practice board from More lamps (once per practice board)
  • set-done you have finished the last of today’s six puzzles (Typeslide, word ladder, nonogram, Quoin, Ligature and this lamps puzzle) and this is the first page to notice it (once a day per browser)
  • reminder-add you tap Remind me every day under “All six done” and the calendar file is made (the time you picked is not sent)

How to play the lamps puzzle

A lamps puzzle is a square grid of white squares and black walls; some walls carry a number from 0 to 4. You place lamps on white squares until the whole board is lit. Lampblack is this site’s daily one, the same for everyone and new at midnight UTC.

The rules

  1. A lamp lights its row and column. It lights its own square and shines up, down, left and right until a wall or the edge of the board stops it. Light never turns a corner and never passes a wall.
  2. Every white square must be lit. A square counts as lit if any lamp shines on it.
  3. No lamp may shine on another. Two lamps in one row or column need a wall between them. If they can see each other, both turn red, with the squares between them.
  4. A number counts the lamps touching the wall. A 2 has exactly two lamps on its four sides (above, below, left, right; corners do not count). A wall with no number takes any number of lamps, including none.
  5. Placing lamps. Tap a white square once for a lamp, a second time for a dot (your note that no lamp goes there), a third time to clear it. On a computer, the arrow keys move and Space does the same cycle.
  6. You never have to guess. Every board was checked by this site’s solver to have exactly one answer that reasoning alone reaches. Hint shows its next step; Check counts your wrong lamps and dots without naming them. Either one caps the day at two stars.

Ways in

  • Zeros first. A 0 dots all four of its sides at once.
  • Full walls. A wall whose number equals its open sides takes a lamp on every one: a 4 always, a 3 against the edge or another wall, a 2 in a corner.
  • Lit squares take no lamp. Every lamp you place settles its whole row and column: none of those squares can hold another lamp.
  • The only light left. A dark square that only one square can still light (itself or one other) needs a lamp on that square.
  • Diagonal squares. A square that would light every possible lighter of some dark square takes no lamp, and so does one that would take away too many sides of a numbered wall: the square diagonal to a 1 in a corner, or the four diagonal to a 3 with four open sides.
  • The weekend’s what-if. Suppose a lamp on a square, follow the simple rules a few steps, and if a square can no longer be lit or a wall can no longer reach its number, the square takes no lamp (or, the other way round, must take one).

Worked example: a 7 by 7

1 0 3 3 0
  1. The 3 in row 4, column 6 has the 0 right below it, so only three of its sides are open: all three take a lamp (row 3 column 6, and row 4 columns 5 and 7). The 0 in row 3, column 2 dots its three white neighbours.
  2. The lamp at row 4 column 5 shines up column 5 to the 1 in row 1, so that 1’s square below it is lit and cannot hold a lamp, and its right side is a wall. Its one lamp goes on its left: row 1, column 4. That lamp lights the rest of row 1 and column 4 down to the other 3.
  3. The 3 in row 4, column 4 already touches the lamp at row 4 column 5, and the square above it is lit. Its last two sides, left and below, both take a lamp: row 4 column 3 and row 5 column 4.
  4. Row 2, column 2 is dotted (it touches the 0) and still dark. The square above it is lit, a wall is to its right and the 0 is below, so the only square that can still light it is row 2, column 1: a lamp there, which lights column 1 all the way down.
  5. Two dark squares are left. Row 6 column 2 has lit squares on three sides and a wall below, so it must light itself: a lamp. Row 6 column 6 sits between a wall and the 0, and the square right of it is lit, so only row 7 column 6 below it can reach it: the ninth lamp. Every square is lit and no lamp sees another.

This board was made for this guide by the same generator and checks as the dailies (one answer, reached without guessing) and is never a daily puzzle. Easy days fall to the steps above; most Friday and Saturday boards also need the diagonal-square idea, and every Sunday board needs the what-if.

Where the puzzles come from

Every board is made and checked by this site’s own code, a year ahead. A generator scatters walls in pairs that mirror each other through the centre, places lamps one by one on dark squares until everything is lit (so a real answer exists from the start), writes each wall’s count of touching lamps as its number, then removes numbers one at a time for as long as the site’s solver can still finish the board by reasoning alone. A board is kept only if the solver finishes it with the four kinds of reasoning above and a separate exhaustive count finds exactly one answer.

The year from 24 October 2026 holds 365 boards: 105 easy 7 × 7 with about 13 walls and 10 lamps, 104 middle 8 × 8 with about 16 walls and 13 lamps, 104 hard 9 × 9 and 52 Sunday 9 × 9 with about 18 walls and 15 lamps, none the same as another even turned or mirrored. An easy board takes the solver about 16 steps; a Sunday board about 34, and every Sunday board needs the what-if. Honest limits: the solver knows four rules and no deeper look-ahead, so the levels are its view of difficulty, not a tester’s; 48 of the 104 midweek boards need nothing beyond the only-light-left rule, so Wednesday is often a step up in size more than in trickiness.

Made with AI tools.