Different parts of your eye are attuned to different frequency responses. For me, it is easier to see flicker in my peripheral vision rather than my direct visi

Different parts of your eye are attuned to different frequency responses. For me, it is easier to see flicker in my peripheral vision rather than my direct vision, so if something is off to the side it can be more annoying than something right in front of me. That said, I can eliminate all annoying flicker by making sure that all of the things that flicker aren't mixing down into ranges that start to annoy me. For example if you have some LEDs that are running at 15Khz and some that are running at 15.1Khz they can set up a beat frequency at 100Hz that is annoying. I had some dimmable can lights that did this and figured out that the PWM was local oscillator based (R/C if you can believe it) rather than crystal based. I found lights that used the line frequency to drive their oscillator so they are essentially all in sync (at 2.4KHz or so, so not noticeable to my eyes)