[ELI5] Why do LEDs in cars flicker? Aren’t they powered by DC?

Question

I understand why we see them flicker in videos, but why do LEDs flicker at all when they’re powered with DC?

In: 2

Answer 1

A simple way to do “voltage conversion” in DC power to reduce the voltage is to not actually do the conversion. Instead, power to the LED is pulsed on and off at high frequency. Rather than pushing half the power to LED, we’ll push 12 volts on a 50/50 on/off cycle at high speed. To the human eye this looks good enough.

To a camera with a shutter time though, you can actually observe the LED in the “off” state if the cycle isn’t quite fast enough.

This is called Pulse Width Modulation (PWM) if you want to read more about it. I hate it, but this is what the industry does.