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.

enter image description here

1 Paraphrased from the original rules on Nikoli

  • $\begingroup$ left top corner is top, right top corner 3rd layer, right? +1! $\endgroup$ Jul 15, 2019 at 11:54
  • $\begingroup$ @OmegaKrypton That's correct, although in this case I think it doesn't matter. $\endgroup$
    – Jafe
    Jul 15, 2019 at 11:56
  • $\begingroup$ @OmegaKrypton Hmm, correction: Actually the order does indeed matter (even though top vs bottom doesn't). Sorry about that. Better add in the layer numbers. $\endgroup$
    – Jafe
    Jul 15, 2019 at 12:08
  • $\begingroup$ Your rules do not say what the numbers are for. $\endgroup$
    – LeppyR64
    Jul 15, 2019 at 12:12
  • $\begingroup$ @LeppyR64 Wow, how'd I miss that? Missing rule added. Thanks! $\endgroup$
    – Jafe
    Jul 15, 2019 at 12:15

1 Answer 1


Like that?

Red = light bulb, yellow = light Solution 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…

  • $\begingroup$ Wow, that was fast. Everything's correct. $\endgroup$
    – Jafe
    Jul 15, 2019 at 12:43
  • 3
    $\begingroup$ The answer would be even better, if the logical deduction for the solution would be present. $\endgroup$
    – BmyGuest
    Jul 15, 2019 at 13:47
  • $\begingroup$ @BmyGuest oh come on, it is too easy :P But added first few moves. Solution took me something under 20 mins, I would be happy for harder. $\endgroup$
    – Jan Ivan
    Jul 15, 2019 at 14:13
  • $\begingroup$ Didn't realize it turned out that easy. My intention was to leave a "unique" starting point, but turns out there was another way to start which you found. (The idea was to begin with row 1 col 1 on #6.) Let's see if I can come up with a "hard mode" follow-up... $\endgroup$
    – Jafe
    Jul 15, 2019 at 14:27
  • $\begingroup$ See? Giving your description helped jafe... I think in the spirit of the site, it's always a good idea to describe the answer better. +1 from me now. $\endgroup$
    – BmyGuest
    Jul 15, 2019 at 14:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.