I would also like to add that DC powered LED lights can flicker as well. To avoid this the current must be extremely "clean." I am noticing this as I power on LEDS and adjust the potentiometer of my power supply. Brand new LEDs flicker, hooked in series, flicker at all setting of the potentiometer. Even at the highest setting there is a flicker but it is at the least of all the settings.
It seems that by adding an inductor(supposedly smooths current) or a capacitor (supposedly smooths voltage), that this can help. But this was supposed done by the manufactures of the power supply. But the more inductors one has the smoother the current can be from what I am reading
What give me hope for right now is electronic ballast and fluorescent tubes. I realize that industry is getting away from this but so far, this seems to be the lighting in an office that can provide the least flicker. I read that with new ballast, approx. 10 dollars, and the proper t8 led tubes. the flicker index rating can be at .01. That type of light is amazing.