The rules
How the light moves
The beam goes in a straight line. A mirror turns it 90 degrees. Land and rocks stop it.
Each night asks you to light a number of the boats out on the water. Every boat can be reached, but usually not all at once, so choosing which ones to leave in the dark is part of the puzzle.
Some nights are calm, some are stormy, in no particular order. Most add one twist: whirlpools, a prism that splits the beam, a pane of coloured glass, or half-turn mirrors that send the light along the diagonals. Coloured light only shows boats with a lamp of that colour, and ordinary boats need ordinary light. Too rough tonight? Submit what you've lit so far, or show a solution.
From the keeper's log
Why not every boat?Because no keeper ever could. A lighthouse can't follow every boat home; it shows the way where the way is hardest. Each night you have a few mirrors, and choosing which boats stay dark is the puzzle.
Every night can be done.Each night is made and then solved by a search that tries every way the beam can go, so the number you're asked to light is the best there is, and it's always within reach. The monthly cyclone is too big for that: its number is the keeper's best, and it can be beaten.
The names are real.Each night borrows the name of a real lighthouse on the coast of Trøndelag and Møre: Agdenes at the mouth of the Trondheimsfjord, Grip off Kristiansund, Kjeungskjær, Sklinna and sixteen more. Twenty of them take turns.
The beam only leaves.Mirrors turn it, prisms split it, half-turn mirrors bend it onto the diagonal and glass colours it, but the light never comes back the way it went. Plan from the lighthouse outward.