Light work: My office at work has two twin-tube fluorescent light fittings, with a gap of about 2 centimetres between the tubes. The tubes were all replaced together recently, and I was intrigued to notice that they were unevenly illuminated, with the appearance of counter-rotating 鈥渃orkscrews鈥�, one inside each tube. These corkscrews had a speed of 2-3 revolutions per second, and the rotation inside each pair of tubes was synchronised. I presume this was caused by an interaction between the plasma discharges in the two tubes, but I would like to know what was happening in more detail and also why the effect faded as the tubes aged over a period of about three days.
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