This is an old photo but a good example of light writing. I took this with a Lumix DMC G1. I used a tripod, 20 second exposure, and f22 to avoid overexposure though there are some blowouts on the floor. It was pretty easy, it worked well on the first attempt. I wrote the word hello normally in the air then reversed the image so it wasn’t mirrored.
I did do a couple of tests leading up to this, here is my first take:
After that I attempted a spiral which looks cool if not like a spiral:
This was a fun and easy experiment. I would not suggest trying this without a tripod, and a remote trigger would be good too. You could also probably get away with using a flat surface and having someone else carefully actuate the shutter.
If you give this a try let me know and shoot me an example, I would love to check it out.