Actually it has to do with how film is shot. Lightbulbs pulse at mains frequency, shoot indoors at 24fps in 50hz land and you'll get a horrible 1hz strobe effec

Actually it has to do with how film is shot. Lightbulbs pulse at mains frequency, shoot indoors at 24fps in 50hz land and you'll get a horrible 1hz strobe effect. There are tricks you can do with shutter angle that negate this, but they are beyond the scope of this comment.