A left-click on the board adds a light bulb to a white square, or removes one that is already there. Alternately you can use arrow keys to move around the board, and press the space bar to toggle light bulbs, or the '1' key to add a bulb, or '0' key or backspace to remove. You can right-click or press the '.' button to put a dot place-holder for a cell that, by your determination, can not contain a light bulb (for instance next to a '0' black cell).

In Assist Mode (0), the default, only the existance of errors or un-illuminated white cells is indicated. In Assist Mode (1), the number of errors and incomplete cells is indicated, see game rules. In Assist Mode (2), errors and illuminated rooms are highlighted with colors. In some cases the solve difficulty will greatly decrease in Assist Mode (2), so select depending upon the level of challenge desired. The game border will turn green if the grid is completed without error. You can click the "undo" button on the bottom of the page to undo previous moves.

Below, enter puzzle code (0-0) for one of a list of pre-defined puzzles, or a puzzle descriptor (see "Puzzles" tab). The following puzzle codes have demos, which will walk you through a solve to help you on the path to mastery: []).

Akari (明かり or "Light"), is a Japanese logic puzzle published by Nikoli. In Akari, the board begins with a collection of black squares, some with numbers, and some without, and white "hallways". The goal is to make sure there is a source of "light" for every hallway, created by the placing of light bulbs. The rules below relate to the numbers, the light bulbs, and how to complete the puzzle.

1. A black square with a number indicates how many light bulbs are adjacent to it, from zero to four.
2. Light bulbs in white squares illuminate all other white squares horizontally and vertically in all directions until the light is blocked by a black square or the edge of the board.
3. To complete the puzzle, all white squares must be illuminated.
4. No light bulb can be illuminated by another light bulb.
5. Light bulbs do not need to be next to a numbered square.

Puzzles can be invoked by either a numerical entry from 0-0, or through a character description of the puzzle itself, entered into the Display form on the 'Game Play' tab. The numbered puzzles are hand-crafted of varying difficulty, roughly easy to hard. Puzzle 0 shows a completed correct puzzle.

To describe a puzzle, the character string must be of the form: "WxH:<descriptor>", where W is a number indicating the width of the grid, and H the height. The descriptor is a list of the black squares with numbers 0-4, or a '*' for a black square without a digit, from left to right, then top to bottom. To assist in the definition of a sparse board, a combination of b consecutive white squares can be represented with a lowercase letter from 'a' to 'z', corresponding to 1 to 26 consecutive squares. A dot '.' can be used as a visual separator, for example between rows. An example descriptor is as follows for entry 1: 'descr'.

For Akari there are 1 demo puzzles that can be helpful to walk through solving methods. They are puzzle codes []. Enter them in the Game Play tab with the code number and there will be added a demo panel to help with the solve.

This playground was written using javascript and is available open source. All code is checked into the github repo at ohmec/puzzles. Feel free to file bugs there!