Flicker isn't intrinsic to LEDs themselves, but rather driver circuits that are efficient and cheap, doubly so for ones that run off low frequency AC mains powe

Flicker isn't intrinsic to LEDs themselves, but rather driver circuits that are efficient and cheap, doubly so for ones that run off low frequency AC mains power. To design a circuit that didn't flicker, first you'd need bulk capacitance to ride out the 100/120Hz AC waveform dips, especially if you didn't want the device to draw peak current around the zero crossing. Then you'd need a high switching frequency and either enough bulk inductance to ride out that off period, or a bunch of bulk capacitance and some wasted power to control the current.