While waiting for a subway train I happened to notice strange swirling patterns inside the fluorescent tubes that are all along the sides of the tracks (hanging down over the border of the platform).
Picture those plasma balls in the science & magic shops. You'd see one of these tubes with corkscrews, others had a rotating line, barber-poles, etc.
A few were OK, giving out an even steady light, but the ones that had the gas swirling around inside made the light seem like it was flickering.
So what's the cause of this? Bad ballasts, improper voltage, cheap tubes (not enough of the white frosting inside), defective tubes, cold temperatures? I thought it was becasue of the cold but it was probably 60 degrees in the underground train station (50 outside in the cold) so I ruled that out.
