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A type of puzzle typically involving a grid of lights, in which the challenge is to get them all to the same state (on or off). The trick is that each light also affects a number of its neighbors, with sides and corners affecting fewer.

A type of puzzle typically involving a grid of lights, the challenge being to get them all to the same state (on or off). The trick is that each light also affects its neighbors, being up to two lights for one-dimensional puzzles, up to four or eight for two-dimensional squares, depending on whether diagonals are defined as adjacent, or up to six, for hexagonal or three-dimensional puzzles.

Example:

+---+---+---+  
| O | X | O |  
+---+---+---+  
| X | X | X |  
+---+---+---+  
| O | X | O |  
+---+---+---+  

If the goal is to get all squares to be O, altering the middle square will solve the grid.

Other variations of this type of puzzle can include cells having more than 1 option and cycling through them as well as different sized grids.