This is a 3 phase LED mains potential indicator in use for 230 / 400 or 240 / 415 Volts 50 Hz with Neutral.

The circuit comprises out of a 2 x 22, 27 or 33 k.ohm 1 Watt resistors, 1N4007 diode, and 1N914 anti parallel diode to protect the led.

The fluctuations are caused because of the different frame rate of the video camera at 24 FPS and the frequency of the rotary converter 50Hz minus the slip 4% is about 49.6 Hz.