Akari (Japanese for art gallery: 美術館) also called “Light Up”, is a binary-determination logic puzzle.

How to Play Akari:

Akari is played on a rectangular grid of white and black cells. The player places light bulbs in white cells such that no two bulbs shine on each other, until the entire grid is lit up.

A bulb sends rays of light horizontally and vertically, illuminating its entire row and column unless its light is blocked by a black cell. A black cell may have a number on it from 0 to 4, indicating how many bulbs must be placed adjacent to its four sides; for example, a cell with a 4 must have four bulbs around it, one on each side, and a cell with a 0 cannot have a bulb next to any of its sides.

An unnumbered black cell may have any number of light bulbs adjacent to it, or none. Bulbs placed diagonally adjacent to a numbered cell do not contribute to the bulb count.

• Video introduction to Akari by Simon Anthony of Cracking the Cryptic (links to puzzle 1, puzzle 2, puzzle 3, and puzzle 4)

Helpful links:

• Akari on Google Play Store (open source, free, no ads/IAPs)

• Akari on F-Droid (open source, free, no ads/IAPs)

• Akari on Apple app store (open source, free, no ads/IAPs)

• Play in browser @ https://www.chiark.greenend.org.uk/~sgtatham/puzzles/js/lightup.html

• To play a specific puzzle, go to “Game…” then click “Enter game ID”. Delete the game ID already there before pasting in your own. Note: the URL will not update to your new puzzle when entered. To get the URL for your newly entered Game ID, use the link that says “by Game ID” located below the puzzle you wish to share.

• Other links (Windows binaries, git, etc.)

• Try an easy puzzle here

• If you want a very difficult puzzle, try this one.