Standard fluorescent lights flicker at 2 times the mains frequency, so 100Hz here, 120Hz there. The little battery powered ones will flicker at whatever frequency the inverter that drives them is running at. One theory is that people get headaches from them because the muscles of the iris are able to follow the flickering.

Some companies now make high frequency fuorescent drivers, often 20kHz or more - these are much better on the eyes.