Light Up

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Moderately difficult Light Up puzzle (solution)

Light Up (Japanese:美術館 bijutsukan) is a binary-determination logic puzzle published by Nikoli. As of 2006, two books consisting entirely of Light Up puzzles have been published by Nikoli.

1 Rules
2 Solution Methods
3 See also
4 External links

[edit] Rules

Light Up is played on a rectangular grid. The grid has both black cells and white cells in it. The objective is to place light bulbs on the grid so that every white square is lit. A cell is illuminated by a light bulb if they're in the same row or column, and if there are no black cells between them. Also, no light bulb may illuminate another light bulb.

Some of the black cells have numbers in them. A number in a black cell indicates how many light bulbs share an edge with that cell.

[edit] Solution Methods

The numbers in the grid often provide key starting points for the puzzle. A 4 must have a bulb in all of its adjacent cells. A smaller number can also force the location of light bulbs if the number is equal to the number of open cells next to it. For example, a 2 in the corner has only two adjacent open cells, since two of its edges are next to the edge of the grid; both cells must have bulbs. Also keep in mind that a light bulb cannot be placed in a cell that is already illuminated by another bulb. For example, if one of the cells next to a 3 is illuminated by a bulb, then the other three cells must all have bulbs.

Conversely, if a cell has the requisite number of bulbs next to it, all the other cells may not have bulbs. This is represented by placing dots in those cells. A 0 can automatically have all adjacent cells dotted.

Another good way to make progress in a puzzle is to keep in mind that every cell must be illuminated. Therefore, if there's a cell that's not lit yet, and only one cell where a light bulb can be placed to illuminate that cell, then you must put a bulb there.