The lamp turns one eighth of a turn every few ticks, round and round, on a fixed clock. Its beam reaches only so far. The clock at the top shows the whole night; drag it to see where the beam points at any moment.
Each vessel sails a fixed course at fixed times (its dotted line and its bar on the clock). Its badge shows the light it needs: white, red (warn it off the reef) or green (the safe channel). Dots under the badge mean a flash code: two dots = two short flashes (dark, flash, dark, flash, dark).
Put pieces on the glowing mounts: Mirror (tap again to turn it), Prism (splits a beam in two, each turned an eighth), Red and Green filters (colour the light after them; the other colour is stopped), Shutter (opens and closes on a timer; tap to change its pattern) and Fresnel lens (throws the beam to full reach again). Fog eats reach three times faster.
A vessel that sees the wrong colour (red for a green ship, green for a red one) is misled and lost. White light never harms.
Press Run and watch the night. Cost = 10 per mirror or filter, 15 per shutter, 20 per prism or lens. Serve every vessel to clear the night; cheap plans earn silver and gold. Hint places a working piece; Ghost shows your best plan.
Keys: arrows pick a mount, Enter places or turns, 1-7 choose a piece, 0 lifts, Space or R runs, [ ] scrub, Z undo, G ghost, H hint, F speed, Esc nights. Pad: d-pad, A place, B lift, Y run, X ghost, LB/RB pieces, triggers scrub, Start nights.