This puzzle is part of the Puzzling Stack Exchange Advent Calendar 2022. The accepted answer to this question will be awarded a bounty worth 100 reputation.

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The year is 1977. Your family is a little bit behind, so even though it's just one week until Christmas, you're finally getting around to setting up the tree. Your dad is doing most of the work, and he's already gotten the tree up and all of the ornaments on it, but now you've found him rummaging around in an old desk drawer, looking through all sorts of pieces of paper you don't understand.

"I can't find the lighting diagram for the tree," he explained. "I planned out the lights and ornaments in a particular way so that the whole tree would be lit up, and I found the plan for the ornaments, but I can't find the one for the lights!"

"Can I help?" you ask, not knowing where you would look for the diagram, but your dad says, "Don't worry," and leads you back out into the family room.

"I knew this would happen, so I made sure to have a backup. Based on how the ornaments are set up, you should be able to figure out where to put all these lights so that you can light up the whole tree. Remember what you learned in physics class - light can only travel horizontally and vertically."

"Dad, I haven't taken physics yet!" you reply, confused. "I'm only nine years old!"

Ignoring you, he continues. "And, if you do, you might even be able to get a hint as to what's in that big present we got you. As the kids say, it's extremely lit - maybe even too lit."

"Dad, kids won't say 'lit' for another 40 years! How am I supposed to figure any of this out?"

"I have faith in you. I'm gonna go run to the convenience store to grab some cigarettes. Good luck - and don't forget the star at the top!" And laying a finger aside of his nose, he hopped into his Oldsmobile and sped off.

I guess you're on your own now. Can you light up the tree before your dad comes home, and more importantly, can you find out what your Christmas present is?

a rectilinear christmas tree with ornaments, some white and some blue with between 0 and 3 white stripes

For a simplified version of the above grid, click here.

EDIT: apologies, missed an ornament! The new one is the leftmost one in the third row from the bottom.


1 Answer 1



ornaments as black cells in Akari, with blue ornaments containing numbers represented by the number of stripes, we get a valid Akari / Light Up puzzle.


the star on top gives a unique solution: completed puzzle with light bulbs


shading the cells that are "too lit", those lit up by more than one source, gives some letters: added shading by number of bulbs seeing each cell which spells out "akari VCS", many thanks to @Chengarda for pointing out the reference, a play on the Atari VCS console released in 1977.

  • 4
    $\begingroup$ rot13(V'z cerggl fher lbh'er ybbxvat ng n cynl ba: uggcf://ra.jvxvcrqvn.bet/jvxv/Ngnev_2600) $\endgroup$
    – Chengarda
    Commented Dec 19, 2022 at 5:18
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    $\begingroup$ yup, @Chengarda nailed it. in hindsight, it might've been a little bit too obscure but I figured someone would get it 😂 $\endgroup$
    – juicifer
    Commented Dec 19, 2022 at 5:19
  • 1
    $\begingroup$ Thanks @Chengarda!! I even have one, but after the rebranding. $\endgroup$ Commented Dec 19, 2022 at 15:43

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