How to play
Every board is a cutting mat with a lamp, a sensor and mirrors in between. Turn the mirrors until the lamp’s beam lights each numbered lens in order and ends in the sensor.
Turning mirrors
A mirror on a round brass turntable leans one of two ways: / or \. Tap or click it to turn it a quarter turn. With a keyboard, Tab to a turntable (arrow keys jump between them) and press Enter or Space. Mirrors on square plates with two bolts are fixed and never move.
In compass terms: / turns a beam travelling north to east, east to north, south to west and west to south. \ turns north to west, west to north, south to east and east to south. Empty squares let the beam straight through.
Lenses and the sensor
Lenses are glass, so the beam passes straight through them. They must light in number order, each once: lens 1, then lens 2, and so on. The sensor only accepts light from its open side, shown by the small arrow. It counts as solved when the beam reaches it after every lens is lit.
What stops a route
- Leaving the mat at any edge.
- Hitting a wooden block.
- Running back into the lamp.
- Lighting a later lens first, or a lens a second time.
- Reaching the sensor before every lens is lit, or from a closed side.
The panel under “The route” says where the beam first goes wrong. It only describes the beam; it doesn’t claim that any particular mirror is wrong. A broken route is normal play: there is no move limit, no countdown and no lives.
Undo, restart and reveals
Undo takes back one turn. Restart puts every mirror back where the board started. Reveal one mirror takes one turntable that is set wrong, turns it to the way it sits in the solution and locks it. A reveal comes from the stored answer, not from reasoning, and the result counts how many you used.
Every board has one answer
Before a board is published, a checking program tries every arrangement of its turntables (2 to the power of the number of turntables, up to 4,096) through these exact rules and a second, separately written beam tracer. A board is published only when exactly one arrangement works and every turntable is part of it.
The daily and your streak
A new daily board starts at 00:00 UTC, the same for everyone. From 17 November 2026, each daily is a new board made for that day, not one from the campaign; the earlier dailies were picked from the campaign collection, so you may have solved those already. Solve the daily on its day to extend your streak. If you started it on its day, you have until 02:00 UTC the next morning to finish it. Past dailies and practice boards are always open but never change your streak.