Lucerna · Free in your browser
Lucerna: Akari Light Up
Place lamps in the open cells until every one of them is lit
Place lamps until every cell is lit. Pure logic — never guessing.
The rules
- Wall
- Lamp
- Place lamps in the open cells until every one of them is lit.
- Place lamps in open cells.
- A lamp lights its own cell and every cell in the four orthogonal directions until a wall blocks it.
- No lamp may light another lamp.
- Every open cell must end up lit.
- A numbered wall has exactly that many lamps among its orthogonal neighbours.
- Two mistakes are pointed out as you play: two lamps that see each other, and a wall with too many lamps, or too few free neighbours left, to ever match its number. A cell that never gets lit, or a wall left short when the rest of the board looks finished, is not marked live — so a full board with no warnings on it can still be wrong.
- Tap an open cell to place a lamp, tap again to remove it. Long-press to mark a cell as definitely not a lamp.
- Every puzzle here is solvable by reasoning alone. You never have to guess.
- Got it
How to play here
Three ways to play
Campaign
Chapters that start gently and bring in one new idea at a time.
Daily puzzle
A new board every day, the same for everyone. Solve every one in a month and that month's trophy is yours.
Endless
Keep going as long as you like, in Easy, Medium, Hard and Expert.
About the game
Lucerna is an Akari puzzle — also published as Light Up — for players who like unhurried, honest logic.
You place lamps in the open cells. A lamp lights its own cell and everything in the four directions until a wall stops it. No lamp may light another lamp, every open cell has to end up lit, and a numbered wall has exactly that many lamps beside it. Two rules pulling against each other, and the numbers saying where the balance is.
Never a guess
Every puzzle has exactly one solution, and every step of it can be reasoned out. Each board is verified by a solver that only uses techniques a person can follow and explain — so a puzzle that would need trial and error never ships. The hint button uses that same solver, which means a hint is always a move you could have found yourself, and it tells you which idea it used.
Learn it by playing it
The rules fit in four lines and the seeing takes longer. The walkthrough hands you real positions and asks for the one cell that follows, then shows you why. No board in it was made up — each is a genuine puzzle stopped at the moment the idea it teaches becomes the forced next move.
Three ways to play, all offline
- 12 campaign chapters, from gentle openings to genuine work
- A daily puzzle, the same one for every player worldwide, with a gentle Monday and a demanding Sunday
- Endless mode in four difficulties: Easy, Medium, Hard, Expert
Measured in months, not streaks
Fill in every day of a calendar month and the month earns its own trophy. There is no streak to lose: a day you missed can still be filled in from the archive, so a week away from the game costs you nothing.
Built to be pleasant
- Warm Material 3 design, light and dark, following your system colours
- Completely offline — no account, no sign-in, no network needed
- One tap places a lamp — no dragging, no typing
- No countdowns you did not ask for and no interruptions
27 languages supported. No account required. Pure logic.
Common questions
Is Lucerna free?
Yes. You can play here without paying and without an account. Ads keep the lights on.
Where is my progress saved?
In this browser, on this device. If you clear the site data, your progress goes with it. A free Solvarium account keeps it safe.
Does it work on a phone or tablet?
Yes. It runs in any current browser on phones, tablets and computers, and the board resizes to fit the screen.
Does every puzzle really have one solution?
Yes. Every board goes through a solver before it ships, and anything with more than one solution is thrown out.