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Lizely

Light Up (Akari)

Solve a fixed 5 by 5 Akari board with touch and full keyboard controls, exact rule feedback, deterministic scoring, and a mechanically proven unique solution.

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How to use

  1. 1.Tap a white cell to cycle clear, light, and X, or use Arrow keys with B or Space for a light and X for an empty mark.
  2. 2.Illuminate every white cell, keep all lights out of one another's unobstructed rows and columns, and match each numbered wall's exact orthogonal light count.
  3. 3.Mark all 20 white cells, then choose Check board or press Enter; a valid board scores exactly 1,000, while two wrong full checks require Restart.

About Light Up (Akari)

Light Up, also called Akari, is a placement puzzle about coverage and restraint. White cells form corridors between black walls. A light placed on a white cell illuminates that cell and every visible white cell in the same row and column until a black wall or the edge of the board stops the ray. The objective is to illuminate every white cell while ensuring that no two lights can see one another. Some black walls carry a number, and that number must equal the count of lights in the four orthogonally adjacent cells.

This version contains one compact 5 by 5 board authored specifically for Lizely. It has 25 cells: 20 white cells, four numbered walls, and one unnumbered wall. The unique completed arrangement uses five lights. The board, clue coordinates, disclosed solution, scoring, and two-error run behavior are product fixtures; they were not copied from either cited source and are not described as an official, historic, daily, or published Nikoli puzzle. Nikoli is cited for the Akari rule set, while Simon Tatham's maintained Light Up documentation independently confirms the same essential constraints.

Play with a mouse or touchscreen by tapping a white cell. Each tap cycles that cell from clear to a light, then to an X mark, and back to clear. An X is only a personal declaration that the cell should remain empty; it does not block a beam. Dedicated Place light, Mark empty, and Clear controls are also available below the grid. Lit white cells receive a distinct surface treatment, while lights or numbered walls involved in a currently visible conflict receive a danger outline to make the rule relationship easier to inspect before checking.

The complete game is keyboard accessible. Use the Arrow keys to move the active cursor through the five-by-five grid. Press B or Space to place or remove a light on the selected white cell. Press X to add or remove an empty mark, Delete or Backspace to clear the selected white cell, and Enter to check the board. Moving onto a wall is allowed so the cursor follows a predictable rectangular path, but placement controls are disabled there. The shared double-Escape gesture opens the boss screen, and the same gesture restores the puzzle.

Checking is deliberate rather than automatic. Every white cell must first be marked with either a light or an X. If even one white cell remains clear, Check board reports that the attempt is incomplete and does not count a mistake. This protects exploratory play from accidental penalties. Once the board is fully marked, the checker reconstructs the light set and applies every puzzle rule: lights must occupy white cells, no pair may share an unobstructed row or column, every numbered wall must have its exact orthogonal count, and all 20 white cells must be illuminated.

A strictly valid full board finishes immediately at exactly 1,000 points. A full but invalid board records one mistake and remains editable, so you can use the highlighted conflicts and feedback to revise it. A second invalid full check deadlocks the run until Restart. Completion and deadlock are terminal states: later clicks, key presses, movement, and checks cannot alter the frozen result. Restart restores the authored clues, a clear 20-cell workspace, zero mistakes, zero score, and the initial cursor position.

The released fixture is verified without trusting a hidden answer comparison. A constraint enumerator starts from an unlit white cell and considers every white position capable of illuminating it. It rejects any candidate light that would see an already placed light or exceed a numbered wall's adjacency count. When every white cell is illuminated, it independently checks exact clue equality, mutual visibility, legal placement, and full coverage. The release test asks the enumerator for up to two distinct solutions and receives exactly one.

That unique solution places lights at zero-based cells 2, 6, 9, 10, and 23, corresponding to row 1 column 3; row 2 column 2; row 2 column 5; row 3 column 1; and row 5 column 4. The clue 2 near the upper-left corner touches the first two lights. The clue 2 below it touches the lights at row 2 column 2 and row 3 column 1. The clue 1 near the upper-right touches the light at row 2 column 5, and the lower clue 1 touches the light at row 5 column 4. None of the five lights see one another, and their wall-bounded beams cover all 20 white cells.

Automated golden checks encode the published rules independently from the board's displayed answer. They verify that a black wall blocks a beam, an unobstructed row is illuminated, a mutually visible bulb pair is rejected, numbered walls use orthogonal rather than diagonal neighbors, an overfilled clue fails, all white cells are covered, and the constraint count is exactly one. Product-state checks separately prove that an incomplete submission records no mistake, the unique fully marked board scores exactly 1,000, two wrong full submissions deadlock, Restart restores a clean state, and both terminal outcomes resist later input.

Everything runs locally in the browser. The game sends no board state to a server, performs no upload, requests no account, downloads no daily puzzle, uses no random number generator, and adds no package dependency. Native buttons provide row, column, wall, clue, mark, and illumination labels for assistive technology. The square five-column grid scales to narrow screens, and the controls maintain touch-friendly targets without depending on drag gestures or hover-only information.

This is a short recreational logic puzzle, not a standardized intelligence test, cognitive assessment, educational placement measure, health screening, or employment benchmark. The fixed board becomes familiar after repeated play, and neither completion time nor number of tentative marks changes the score. A useful solving approach is to start with numbered walls: determine which adjacent white cells can still hold their required lights, then mark impossible cells with X. Next trace each dark corridor to find cells that have only one possible source of illumination, while continually checking that two candidate lights would not see each other across an open row or column.

Methodology & sources

Represent the 5 by 5 product-authored board as 25 explicit cell records. Trace light visibility in four orthogonal directions, stopping at the edge or first wall. Validate legal bulb cells, mutually visible bulb pairs, exact numbered-wall adjacency, and illumination of all 20 white cells. Independently enumerate solutions by choosing the first unlit cell, branching over every visible candidate source, pruning mutual visibility and clue overflow, deduplicating complete bulb sets, and accepting only full rule-valid boards. Runtime checking requires every white cell to be marked, awards exactly 1,000 only for a valid full board, counts no error for an incomplete check, deadlocks on the second invalid full check, and freezes both terminal states.

Frequently asked questions

What stops a light beam in Light Up?
A black wall or the board edge stops the ray. X marks and other ordinary white cells do not block illumination.
Do numbered walls count diagonal lights?
No. A numbered black wall counts only lights in its up, down, left, and right neighboring cells, and the count must equal the printed number exactly.
Does this fixed puzzle have only one solution?
Yes. The release test uses constraint enumeration under all cited rules and finds exactly one solution, containing lights at cells 2, 6, 9, 10, and 23 in zero-based order.
Is this an official Nikoli puzzle or an intelligence test?
No. Nikoli is cited only for the rules. The board is a Lizely-authored recreational fixture, and its fixed score is not a standardized cognitive, health, education, or employment measure.

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