Flicker is following the electrical current fluctuations. So, when in europe use a shutter speed dividable in 60 Hz. eg. 1/30, 1/60, 1/120 etc.... In US.... dividable in 50 Hz, eg 1/25, 1/50, 1/100 etc. "Flicker is usually a potential problem only with lighting that requires the use of ballasts, like fluorescent lights. Incandescent lights usually do not cause a flicker problem since the light filaments generally do not cool quickly enough (and make the light dimmer) during the "off" time as the voltage changes in the AC power line.
The type of ballast, which controls the electrical supply to fluorescent lights, affects the amount of flicker. Magnetic ballasts change the voltage supplied to the fluorescent lamps but do not alter the frequency - the power line frequency of 60 Hz. The ultraviolet (UV) light produced inside the fluorescent light tube also fluctuates 120 times per second. The phosphorescence (the fluorescent light) resulting from the UV shining on the phosphor coatings inside the light tube is sufficiently stable (i.e., lasts long enough) to even out the variations in the fluorescent light output."
