1. All five windows start dark. Each visitor arrives exactly once. Nobody else changes the windows.
2. A visitor first counts how many of the three listed windows are lit. Other windows do not count. The account is always truthful.
3. The visitor then flips the two specified windows: lit becomes dark, and dark becomes lit. Both flips happen before the next visitor arrives.
4. Place every visitor in chronological order. Every account must agree with the window states immediately before that visitor acts.

For example, if only windows 1 and 4 are lit, a visitor looking at 1, 2 and 5 sees one lit window. If they then flip 1 and 3, the next visitor encounters windows 3 and 4 lit.

A statement fitting now does not guarantee a correct placement. Trace its consequences. Since every visitor acts once, the final lighting pattern is the same in every order: the intermediate observations are what identify the history.

Pencil marks hold possible witnesses in empty visits. Assigning an already placed witness swaps the two visits. Undo reverses an edit; Clear empties the selected visit. Keyboard: A–F places a witness, 1–6 selects a visit, ↑/↓ moves between visits, N toggles pencil, and Delete clears.

First case has four visitors and a direct deduction at every step. Daily and practice cases have six visitors and more than one plausible first arrival. Hints offer a nudge before revealing a branching choice. Progress, including practice, stays in this browser; a new daily case uses the Amsterdam date when the page opens.

Lamplog is a working title for this redesigned prototype. Unlike the previous sum-ring game, the clues describe changing moments: every witness also causes the next scene. Print a blank case to solve with a pencil; write the visitor letters in order and track the lit windows after each visit. The web interface only does that bookkeeping for you.

A September 2026 search found no exact match for the combined observation-before-action rules. Related games include Switchboard (choose switches to reach a final pattern) and Chronologic (order historical events). This is not proof of worldwide novelty or a copyright, patent or trademark clearance. Independent puzzle-editor review and publishing advice are still needed before claiming a newly invented genre.

The design preserves evidence-based motivations: closing an information gap, and supporting competence and autonomy with reversible choices, visible consequences and optional help. Enjoyment and book-length variety still need reader testing.