while I was sitting in city center with so many LED (especially red ones mounted) signboards and I was bitting an apple, the signboards suddenly begin to shake for only a second while my head is shaking.
I couldn't understand why this had happened to my eyes? Maybe the XTALs in the LED-driver-circuits are out of the frequency because of high voltage or so many times these are used, and/or grid's frequency has been added on to the device.
What should be done to prevent this frequency shake?
Is this topic belongs to harmonic distortion - THD ? That maybe a reason by XTAL's frequency?