Why does a flickering fluorescent light blink faster when you wave near it?

Fluorescent lights powered by alternating current (AC) flicker very rapidly—120 times per second (120 Hz) in North America, 100 Hz in many other countries (Wikipedia). Normally, our brains smooth out this flicker and we perceive steady light (Arrant-Light). However, when you wave your hand under one of these lights, you slice through the flickering pulses. Instead of seeing a continuous blur of your moving hand, you see many frozen images illuminated by each tiny flash. This is called the stroboscopic effect, and it makes the flicker suddenly obvious (Arrant-Light).

Your hand movement effectively 'samples' the light at intervals, like frames in a film, revealing the brief dark moments between flickers that your eyes usually ignore (Arrant-Light). The light isn't blinking any faster; your hand just helps your brain notice what's been happening the whole time.