Some LED lights/bulbs also incorporate phosphorescent materials and use UV LEDs to stimulate the phosphor which helps too. This is also one of the ways better colour reproduction can be achieved. This comes at a slight efficiency cost though, I think.
Most LED lights use the UV+phosphor technique as its cheaper than doing RGB (If the LED is yellowish when switched off, its using this technique).
The best flicker-free lights are ones that have low ripple constant current power supplies (somewhat expensive). LED lamps intended for use around rotating machinery used to all be this way until someone figured out that if the PWM frequency was wildly unstable it would prevent the problems with strobe lights around spinning things at a fraction of the cost.
