It's complicated to understand, even more me, but there are basically safe frame rates and shutter angle combinations. If you are shooting at 24 fps with a 144 degree shutter angle (1/60th of a second), you basically get two pulses per frame from a 60 Hz light -- same for a 25 fps camera with a 180 degree (1/50th) shutter shooting a 50 Hz light.
So a good starting point when setting the shutter on a video camera is to pick a shutter time that is 1/60th or 1/30th for a 60 Hz light (even 1/120th works I believe, but that's only one pulse captured per frame.) But that's only a starting point, you may need to play around a bit using the ECS.
The formula is any frame rate that divides evenly into twice the power frequency is safe. 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 24, 30, 40, 60, 120 fps for 60 Hz.
Anyway, here's a chart:
Someone how understands math and electricity can explain it better than me...
But the principle is that flicker occurs when each frame exposed is getting a slightly different exposure than the proceeding or following frame, and this exposure variation appears as flicker. So there are certain combinations where the amount of AC pulsing captured is consistent frame to frame, and there are combinations where it isn't.