This is a three-dimensional Akari puzzle (also known as Light Up). The six squares represent the layers of a $6\times6\times6$ cube, top to bottom. The objective is to add light bulbs into any number of cells so that the resulting grid satifies the following rules:1
- Black cells are walls and cannot contain light bulbs.
- Numbers in black cells indicate how many light bulbs are directly adjacent to that cell (vertically, horizontally or along the Z-axis).
- A light bulb illuminates its own cell as well as every cell visible from it in all six directions (up/down, right/left, and both ways along the Z-axis), continuing until a wall comes in the way.
- Every white square must be illuminated by at least one light bulb.
- No light bulb may be illuminated by another light bulb.
Note: The solution is unique and solvable by logic alone. No guesswork or trial-and-error is necessary here.
1 Paraphrased from the original rules on Nikoli
Red = light bulb, yellow = light Start from bottom
1 because you can't place light bulb above (in z) "2" and next to "1" can be only one, so it has to be there.
2 because you can't place light bulb above (in z) "2" and there is already light from first light bulb
3 since second light bulb eliminates one solution
4 because 1st and 3rd light bulbs eliminates rest
5 because of 4th and so on…