I am now curious. Does anyone else experience this?

Back in the olden days, I remember LED clocks would light up solidly. I could turn my head quickly, or even just swivel my eyes, and the solid bars of the 7-segment display would stretch out into lightsabery lines. But the display in our car was different–it was actually blinking very rapidly, so that if I turned my head quickly (or just an eye swivel) it would briefly appear as a dotted line. Does anyone else experience either of these?

When I got into electronics, I learned that a common technique is “multiplexing”, which requires less electronics and is therefore cheaper to produce. The single circuit that produce a single digit rapidly cycles through all the possible digits, only lighting up one-at-a-time. This happens too quickly for the human eye to perceive, so it looks solid–a phenomenon called “persistence of vision”–which is also why television and movie screens seem continuous.

With the advent of LED lighting, I am noticing this more and more, including on brake lights of cars, and even some forms of indoor lighting. My daughter recently bought a string of decorative lights to string around her room, and on anything but full-brightness setting, it flickers in a way that hurts my eyes. The LEDs are dimmed by rapidly cycling them on and off (pulse-width modulation) and I can clearly see the dotted-line effect with an eye swivel, but she can’t.

What are your experiences? Pretty much all LED clocks these days use multiplexing. Can you see the flicker? Do you have other experiences that give you visual overload?