A few weeks before Halloween, we were at the movies waiting for the movie to start when we sparked the idea of throwing a Halloween party. But not just any party... An elaborate Harry Potter Halloween party. By the time the previews ended, we had researched and planned almost every detail.

We wanted to turn the hallway of our apartment into the Great Hall of Hogwarts. Specifically, make a set of floating candles that would magically move up and down. Every store was sold out of magic so I decided to invent some of my own.

We measured all of the walls and made a model of the apartment in Sketchup. To figure out what these floating candles might look like, I used this model to place candles in a pattern on the ceiling of the main hallway.

We would move the candles up and down using a motor. The motor would spin four 6-inch diameter disks connected with pegs spaced by 90° along the edges of the disks. Fishing line would be loosely tied around each connector, and the lines would run up to the ceiling and through hooks to suspend the candles in the air. When the motor would run, the connectors would move closer to and farther away from the hooks making the candles move up and down.

Each line had three or four candles attached to it. The junction point between each candle's segment of line to the segment before it would be around 1 foot closer to the motor than the previous candle's hook. This would mean the line of candles could be pulled on the motor end to move the candles up and down together. By using three different lines, the candles would look like they're moving randomly.

To keep people from hitting their heads on the candles directly above, the middle five candles were stationary and closer to the ceiling.

In the shop we make a few candles with tea lights and poster board. Instead of using fishing line, we used FireLine beading line. The stuff is braided and difficult to cut with normal scissors. It also turned out to be virtually impossible to see against the hallway ceiling.

We took the motor out of an oscillating floor tower fan. It went the right speed, was quiet, and was AC powered, which was nice since it would operate next to an outlet. Many of the other motors we tried were battery-powered and not torquey enough.

You can see the disks in the first picture that were connected to the motor. We tested it by putting three hooks into the ceiling, running each line to one of the pegs between the disks, and ran the motor. The candles moved up and down in three phases as expected.

Back at the apartment, I used the 3D model to measure the location of each candle on the ceiling. I also adjusted the heights of the candles to look more random.

I sketched the configuration into a notebook and wrote down the measurements relative to the walls and each other.

The hallway was almost 16 feet long and my tape measure could just make it. Above each candle would be a hook that the candle's line would slide through. I used the measurements in my notebook to mark where each of the hooks would need to be.

Shortly before this, I accidentally ordered 500 envelopes from Amazon. Oops, I only wanted 100. This meant I was using envelopes for everything, so I taped a bunch together to mark the longitudinal position for each hook. I would also mark the lateral distance to the wall.

The hooks had roughly ½ an inch of thread and were screwed directly into the drywall. The open side of the hook faced outwards in case the line wanted to ride up. You can see two markings on the envelopes for hooks both 11 inches away from the wall.

Once the hooks were up, I started to string some lights. I tied a knot of the line around the base of the tea light's "flame" and used scotch tape to center the line on the tip of the flame. If the line wasn't connected to the tip, the whole tea light would hang sideways. The ends of the lines in these pictures were tied around the handle of the door just out of view.

Now I wanted to make the lights move and make sure this was going to work.

Below you can see the motor attached to the disks. The pegs between each disk needed to be strong enough to hold the disks together. There couldn't be a supporting rod through the center of the disks or the line would get wound around it. There needed to be two pegs per space so that the disks wouldn't become misaligned. Slits were cut into a plastic top to keep the lines centered and unlikely to rub against the disks.

I used zip ties to provide connection points to the ends of the lines for the motor and the lights. This meant we could disconnect the motor from the lights without taking them down from the ceiling. We would connect the zip ties using pipe cleaners. This worked well because it would stay in shape without stretching and it was lightweight.

The second picture shows how invisible the line was when it was against the wall. As a result, it looked like the pipe cleaner was floating.

Each light started with its own line that was long enough to connect to the halfway-ish point of the line before it. The lines were connected with superglue. If I did this again, I would use a clasp connection instead of superglue. Many times during work on the ceiling, I ran into a line I couldn't see and tore the lines apart. This would have a domino effect and rip the lines for the rest of the lights in the chain.

Now it was time to make the candles using poster board. We found PVC pipe that was the same diameter as the tea lights, so we cut it into 1-inch sections. We then wrapped the poster board around the tea light at the top and the PVC ring at the bottom. This helped keep the candle in shape.

For a more wax-like appearance, we dripped hot glue down the sides of the candles.

The hooks were somewhat visible but it wasn't distracting. If the forced air was running in the apartment, the candles would sway a bit.

The batteries that came with the tea lights lasted over two weeks of continuous use.

At the end of the hallway just inside the front door, we hung sheets of material like table cloth that had a brick wall pattern on it. We hung two sheets side by side so that it was easy to walk through into the hallway. Above the brick wall was a sign we made for Platform 9¾.

Turning on the lights meant individually switching the power on the bottom of each light. To make this easier, we poked holes in the sides of the candle's poster board that was wide enough to fit a small screwdriver.

You can see the lines that crossed over the recessed ceiling light. Shining light onto the lines was the best way to see them, so working on the lines was easier with a flashlight.

The party was a success and the floating candles were a surprise and delight for our friends, welcoming them into the Wizarding World. We left the candles up for a while after the party. Before taking them down once Halloween had passed, I took a video showing how it worked.

One of Clarke's three laws says "any sufficiently advanced technology is indistinguishable from magic." While this was anything but sufficiently advanced technology, it was not necessarily unmagical.