Here are my entries:
First one was made mainly to learn how to make and edit a video with Blender.
Also, it was quite a surprise to find such a rare type of light bulb in one of my own junk boxes. I didn't knew such a thing even exists, never mind that I was having one:
https://youtu.be/p2XPMuDMxwoThe video for the real entry was only half-edited, and sent in the last minute before the deadline:
https://youtu.be/V7gQh1KFjqcThere was no time to add explanations in the second video, so it's probably dead-boring to watch.
It is made by 2 identical motors, each with 4 magnets on top, and a reed switch nearby. The 2 magnetic reed switches are in series with a light bulb and a battery. The motors rotate the magnets they have on top of their axle producing a rotating magnetic field.
When the motors are at the right distance from the switches, the reed contacts start to vibrate in the rhythm of the rotating magnetic field. Motors rotate very fast, probably around 2000 RPM.
The trick is that each motor has a slightly different RPM. The reed switches are in series, so they emulate a logic AND for the bulb. Boolean AND is the same as multiplication. Multiplying RPM1 and RPM2 corresponding frequencies will produce two spectral components with the frequency RPM1 + RPM2 and RPM1 - RPM2, because cos(x)cos(y)=1/2[cos(x?y)+cos(x+y)]
As a result, the bulb filament will see two frequencies, RPM1 + RPM2, and another frequency RPM1 - RPM2. Because the filament has thermal inertia, it will act as a low pass filter, and it will attenuate the component of frequency RPM1 + RPM2.
On the contrary, RPM1 - RPM2 will be in the range of about 1 Hz, and the light bulb will flash in the rhythm of RPM1 - RPM2.
In the end, we managed to produce a 1 Hz oscillation started from 2 motors at about 2000 RPM.
Same technique as used in telecommunication for frequency shifting, frequency modulation, software define radios, etc., but applied to an incandescent light bulb with the help of 2 reed switches.