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Spirograph - OC - method below.
(i.imgur.com)
Took a colour changing lightbulb and put it into a sealed empty Pringles can. Suspended this from a frame by the power cable. Made a small hole in the Pringles can for the light to come through. Pointed camera upwards and took a long exposure of the swinging can whilst changing the colour of the lightbulb using the remote. Really happy the way it turned out. (Was the third attempt after trying with laser pens, etc.) It really simple to set up and you can generate a lot of different effects.
Excuse the mess but was experimenting. :-) If you want to know more let me know.
Thanks for sharing! This photo helped a lot understanding the process you described in the post. Way simpler than I thought for such a cool result!