Halifax Makerspace was invited by our local library to an afternoon of tech and crafting. After our plans of an intro to soldering course fell through (no soldering permitted due to fire regulations), we were forced to be a bit more creative. For our part of the program, we wanted:

people to be able to drop in any time during the program and be able to complete the craft in a few minutes
to send people home with something cool
to introduce the concept of a circuit, and demystify electronics in general
to showcase our Makerspace's laser cutter
to be able to reuse some of the work we put in to designing the course for other events in the future
to do all this very cheaply

What we decided on was an acrylic ornament in two pieces, with an LED in the base lighting the ornamental part. Copper tape would make the connection between a lead of the LED and a button cell battery.

You could do any size batch of these for a makerspace open house, a Cub Scout troop activity, for everyone on a Christmas list, wedding favours, or just cut one for yourself.

Materials (Total cost for us: about $0.25-0.30 per ornament)

1/4 inch acrylic - we got a lot of small offcuts free from the Discovery Centre when they moved, and some from a recent Little Free Library build
2032 batteries - ordered from Aliexpress for about $0.20 each
LEDs - We gave people choices of yellow flickering (candle), red blinking or regular white. They cost a few dollars per hundred from Aliexpress. We were surprised to find the normal white LEDs were the most popular
5mm copper tape - about $4 for 30m from Aliexpress

Step 1: Prepping the Base

We decided on a reusable generic base, in case we wanted to do a similar events for other holidays in the future. Features of the base:

our logo and website engraved, with a warning to keep out of reach of children (the small battery can be removed easily)
the positive side of the battery hole is marked with a "+"
two holes for the ornament's "legs" to slot into
two holes for the LED's leads
a rectangular hole to press fit the battery

It took some testing to get the battery hole exactly right. We wanted to make sure it press fit in place (with a LED lead and copper foil), and that it didn't press in so far that it came out the bottom.

ornamentbase-generic.svg
Download

Step 2: Designing the Ornaments

This is the fun part. Choose a theme, make or find some vectors, and cut and engrave them. Some svg files are included. We did a snowman, Christmas tree and menorah (menorah by Real O'Neil).

A few design notes, though:

the generic base means you can reuse the bottom segments of the ornament.
you need a shoulder to make sure the tabs don't go too far in.
etching lights up best in a "V" above the LED, so taller and narrower is better.
etching takes a lot longer than cutting. Be prepared for this, or minimize the amount of etching.
the light doesn't travel well around holes in the acrylic, so try to keep a solid shape without too many cuts coming far into the ornament. The menorah shown above didn't light up well with the flickering yellow LED, but looked great with a solid white.

Step 3: Assembling

Okay, I lied in the last step. This is the fun part. Assembly is super easy, and lets you talk to people about electronics and laser cutting. Make the most of this.

Each person gets a base, a choice of ornament, a battery, an LED (we gave them the choice of pure white, flickering yellow, or blinking red), about 2 inches of copper tape and some tape. Put the LED leads through the holes, with the longer lead (the positive one) closest to the battery hole. Bend the positive lead up through the hole, then over a bit on top towards the engraved "+" to keep it from coming back through. This will be the positive terminal.

On the other side of the battery hole, stick some of the copper tape (with backing removed) up through the bottom so it comes out the top slightly. Stick it to the side of the battery hole away from the "+". This will be the negative terminal. Turn the base upside down and begin adhering the copper to the base's bottom. Now you need to make a 90 degree bend to get the copper tape to the unused negative lead of the LED. To do this with copper tape is a little counterintuitive. You can't simply cut the tape and stick it to itself, as the adhesive won't conduct current reliably over time. To make a 90 degree turn, you turn the tape upside down and make a 90 degree turn in the opposite direction you want to go. Then fold it rightside up, covering the bend you just made, which gets you back in the direction you want to go with the adhesive side down. When you've laid down your copper tape, bend the remaining LED lead down over the copper, then fold the end of the copper up over the lead. This is a bit tricky to describe. See the attached diagrams. If the lead is a bit long, make a little hook on the end to increase contact with the copper, then tape this down with Scotch tape. Your base is complete.

Test it by inserting a battery so the flat side (positive), presses the LED lead to the "+" side of the battery hole. If it doesn't light, either the LED or battery could be backwards, or one of the connections is loose (most probably the copper tape/LED connection).

Pop your ornament into the slots and enjoy!

Step 4: Taking It Further

We were limited by several factors in doing this project. If you don't have these limitations, you might consider:

soldering the connections (you can solder to the copper). We couldn't solder at the library due to fire restrictions
letting people paint the back of the ornament
etching personalized names/faces if you are doing this where your laser cutter is set up. Perhaps you might do all engraving except the personalized part beforehand, to save time.
make a more complicated circuit: multiple LEDs, alternating colors, adding a light sensor to turn it off during the day, etc.
etch a circuit diagram onto the base

A Note About This Circuit

LEDs usually are used with a current limiting resistor which results in a longer life for the LED. We chose not to use one in part because we felt the amount of current delivered by the battery is low enough that we will get a sufficiently long lifespan from the ornament, but mostly because, given our lack of permission to solder, we felt the two extra connections needed for a resistor would likely be more troublesome than the reduced LED lifespan. You could certainly add one if desired.