Incandescent bulbs flicker at the rate of the AC current, but the flickering is brighter/dimmer rather than on/off because they stay radiant while hot and cool slowly.
Yes but I guess the amplitude of the flicker must be very low? I'd have thought that if it was at all significant it would be very visually obvious at 50-60Hz
But you can stabilize the current quite nicely if you know how. This is almost never done on cheap LEDs. Except IKEA's leds, they were surpricingly good in some test lately.
