Play a free Akari puzzle in your browser by loading a fixed 5 by 5 Light Up board, marking every white cell with a light or an X, and finishing on a deterministic 1,000-point score. Akari, also called Light Up, is a placement puzzle about coverage and restraint: you put a light on a white cell and that beam travels along the row and column until a black wall or the board edge stops it, illuminating every visible white cell along the way. The objective is to illuminate every one of the 20 white cells while ensuring that no two lights share an unobstructed row or column. Four of the black walls on the board carry a small number, and that number must equal the count of lights in its four orthogonal neighbors exactly. The published rule set is owned by Nikoli under the Akari name, while Simon Tatham's maintained Light Up documentation describes the same essential constraints, so the same logic carries across both titles. A free online version is offered as a browser-only fixture: no download, no account, no daily download, and no random board, so the same 5 by 5 puzzle is solved every run.
Light Up (Akari) Rules in Plain English
An Akari board is a square grid divided into two kinds of cells. Most cells are white and serve as both the corridors that lights must illuminate and the only legal homes for a light. The remaining cells are solid black walls. Some walls carry a small printed number from 0 to 4; the rest are unnumbered and only act as beam blockers. Once you place a light on a white cell, its beam travels in the four orthogonal directions, up, down, left, and right, and keeps going until it hits a black wall or the edge of the board. Every white cell the beam touches becomes illuminated, including the cell that holds the light itself. Two lights may not share an unobstructed row or column, which means their beams must be separated by at least one black wall or by the board edge. Finally, every numbered wall is checked against the four orthogonal cells around it, and the number is exactly the count of adjacent lights.
The result is a placement puzzle with two competing pressures. You want enough lights to cover every white cell, but you do not want so many that they conflict with one another or overflow any clue. A 5 by 5 board is small enough to hold in working memory but dense enough to demand real logical pruning. Most candidate placements can be ruled out before they are placed, which is why the genre is grouped with paper-and-pencil logic puzzles rather than arcade games. The free Akari browser fixture ships one such board, with 25 cells total: 20 white cells, four numbered walls, and one unnumbered wall, and its unique completed arrangement uses exactly five lights.
What marks mean on the board
White cells cycle through three states: clear, light, and X. The clear state is the default and means you have not yet decided. A light is a real placement that contributes its beam and its adjacency count to every numbered wall it touches. An X is a personal note that the cell should remain empty; it does not block a beam and it is invisible to the rule checker. Lit white cells get a distinct surface treatment so you can read the coverage map at a glance, and any light or numbered wall caught in a visible conflict receives a danger outline so the relationship is easy to inspect before you commit.
Play a Free Akari Game in Your Browser
If you are looking for an Akari game you can play free without installing anything, the Light Up (Akari) fixture runs directly in your browser on a fixed 5 by 5 board. The same puzzle is loaded every time you open the page, so you can compare attempts against a known target instead of guessing which version you got. Everything runs locally in the browser: no board state is sent to a server, no upload is performed, no account is required, and no daily download replaces the published fixture.
- Open the Light Up (Akari) page in any modern desktop or mobile browser; the 5 by 5 grid scales to fit the available width without losing its square shape.
- Tap a white cell to cycle it through clear, light, and X, or use the Arrow keys to move the active cursor and press B or Space to toggle a light and X for an empty mark.
- Place lights so every white cell ends up illuminated, no two lights share an unobstructed row or column, and every numbered wall counts exactly the right number of adjacent lights.
- Mark every one of the 20 white cells with either a light or an X before you check; leaving even one cell clear triggers an incomplete response and is not counted as a mistake.
- Choose Check board, or press Enter, to score the attempt; a strictly valid full board scores exactly 1,000 points immediately.
- If a full check returns invalid, read the highlighted conflicts and revise; a second invalid full check deadlocks the run and the puzzle must be Restarted to play again.
Touch and Keyboard Controls
The same board is fully playable with a mouse, a touchscreen, or a keyboard. On touch devices, tap a white cell to cycle it. On a desktop, you can either click cells the same way or drive a cursor through the grid with the Arrow keys. Moving the cursor onto a wall is allowed and follows a predictable rectangular path, but the placement controls are disabled on a wall so a stray key never plants a light on an illegal cell.
| Action | Touch or Mouse | Keyboard |
|---|---|---|
| Place or remove a light on the selected white cell | Tap or click until the cell shows a light | B or Space |
| Add or remove an X mark | Tap or click until the cell shows an X | X |
| Clear a marked white cell | Tap or click until the cell returns to clear | Delete or Backspace |
| Move the cursor through the grid | Click any cell | Arrow keys |
| Run a check | Choose Check board | Enter |
| Open or close the boss screen | Double-tap a shared gesture | Escape twice |
| Reset to a fresh puzzle | Choose Restart | Restart control only |
Lit cells receive a different surface treatment so coverage is visible without re-reading the lights list, and lights or numbered walls caught in a visible conflict receive a danger outline. Native button labels expose row, column, wall, clue, mark, and illumination terms to assistive technology, and the touch targets are sized so that drag gestures and hover-only states are never required. Everything runs locally, which means the same free Akari game behaves identically on a phone, a tablet, and a desktop without depending on a particular operating system.
Scoring, Checking, and the Restart Rule
The free Akari browser fixture scores with a deliberate, deterministic formula rather than a timer or streak counter. Checking is a manual step, never automatic, and it has three possible outcomes depending on what you have marked when you press Enter.
If even one white cell is still clear, the checker reports that the attempt is incomplete and does not count a mistake. This protects exploratory play, where you might want to test a partial placement before committing to the rest of the board. Once every one of the 20 white cells carries either a light or an X, the checker reconstructs the light set and applies every rule at once: lights must occupy white cells, no pair may share an unobstructed row or column, every numbered wall must have its exact orthogonal count, and every white cell must be illuminated. A strictly valid full board finishes immediately at exactly 1,000 points.
A full but invalid board records a single mistake and remains editable, so you can use the highlighted conflicts to revise without losing the run. A second invalid full check, however, deadlocks the puzzle and the run can only continue after a Restart. Both terminal states, completion and deadlock, are frozen, which means later clicks, key presses, cursor moves, and additional checks cannot alter the recorded outcome. Restart restores the authored clues, a clear 20-cell workspace, zero mistakes, zero score, and the initial cursor position. Completion time and the number of tentative marks do not influence the score, and the same fixture can be replayed without being randomized. The full rule set and the independent enumeration that produced the unique 5 by 5 answer are described in Simon Tatham's Light Up documentation.
解 5 乘 5 的 Akari 謎題板
已發布的固定題盤共有 25 格，其中包含 20 格白格、四面有編號的牆，以及一面無編號的牆，而其唯一的完成排列恰好使用五盞燈。發行測試會獨立地在每條規則下枚舉整個約束空間，以確認存在唯一解，因此你可以對照一個已知答案來檢驗自己的解題結果，而非僅對照一道隨機產生的題目。按照規則實際約束你的順序來解題會更容易。
從有編號的牆開始。對每個提示，列出它的四個正交相鄰格，並詢問其中哪些格仍然可以放置燈。提示為 0 代表四個相鄰格都必須是 X。提示為 1 代表恰好有一個相鄰格是燈，其他三格是 X。提示為 2 代表恰好有兩個相鄰格是燈，其他兩格是 X。一旦你寫下這些要求，請將每一個無法放置燈的相鄰格標記為 X，因為 X 標記是個人的筆記，永遠不會擋住光束。一個實用的捷徑是注意：當提示為 1，且只剩一個相鄰格能夠放置燈時，該格就必須點亮。
接下來，追蹤每一條黑暗通道，也就是一排由牆所界定的白格行或列。通道中的每個白格都必須由通道內部照亮，因為光束無法穿越牆。計算該通道中有多少個白格；這就是它至少必須包含的燈數。如果數量為一，則通道中唯一的格子就必須是燈。如果數量為二，則這兩格構成一組候選對，你可以立即檢查同時放置兩盞燈是否會在垂直交叉的通道中與另一盞燈產生互相照亮的衝突。在放置候選燈時，請持續重新檢視危險輪廓；如果一盞燈能在開放的行中看到另一�燈，則在兩者都被放置時，該配置會立即被否決。
最後，請在標記完每個白格之後才執行「檢查題盤」步�。這個確定性的 1,000 分結算機制，是為了避免部分提交不小心鎖定一個低分數，同時也讓已經理解規則的玩家能夠對照一個已知的固定題盤來檢驗自己的解題過程。所引用的 Nikoli 規則以及 Simon Tatham 的 Light Up 文件描述了同樣的核心約束，因此你在這個 5 乘 5 題盤上建立的詞彙可以轉移到更大的 Akari 格子：有編號的牆僅計算正交相鄰格、X 標記不會擋住光束，而唯一答案就是那個使每個白格恰好被照亮一次的排列。
如需更深入的探討，請參閱Circuit Logic Game：五道布林益智題通往 TRUE。
如需更深入的探討，請參閱免下載的邏輯格子題：瀏覽器直接玩。