Light Up
Place lighbulbs in the grid so that every white square is illuminated. Lightbulbs illimunate all squares they can see horizontally and vertically. They are blocked by black squares. Lightbulbs aren't allowed to see eachother. Number clues in black squares tell you how many lightbulbs there are in the 4 squares touching it.
Example
There can't be any lightbulbs around the 0 in row 1. The square in the left top corner can now only be illuminated by a lightbulb in the first square of row 2. The square in the right top corner can now only be illuminated by placing a lightbulb on it.
Now there's one lightbulb next to the 1 in row 2, so there can't be a lightbulb under it. Now the square in the right bottom corner can only be illuminated by placing a lighbulb on it.
There can't be a lightbulb on the second square of row 3 as there wouldn't be room to place a second lightbulb around the 2 in row 4. This lightbulb would then see the lightbulb in row 3, which isn't allowed. Thus the second lightbulb next to the 2 in row 3 has to be below it. Now we can place the final lightbulb above the 2 in row 4 and the puzzle is done.
Background
This genre was invented by Nikoli and is also known by the name Akari.
Puzzles in this genre.
