Mains powered lights often do flicker, but it's fast, and in most types of lights, the output doesn't go to zero, even though the input power goes to zero momentarily. As coppice pointed out, incandescent bulbs produce light according to the temperature of the filament, and the filament does not heat up or cool down instantly, so the light output is much smoother than the electrical power input.
But if you watch telecasts of athletic events that are held indoors or at night, when they have a slow motion replay captured by high speed camera, you'll often be able to notice the flicker of the lights. The flicker is often slowed down to a couple of Hertz on the slow-motion replay. I'm not sure of the lighting technology used, but it's probably not incandescent filaments. I don't watch a lot of sports, but I noticed the effect during the Olympics, and most recently during the baseball World Series.