Why do some tail lights appear to flicker in dashcam videos?

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Why do some tail lights appear to flicker in dashcam videos?

In: Technology

I am by no means an expert so this can suffice until someone more knowledgeable comes along.

As I understand it, the lights on a car are in fact flickering (strobing) at a certain frequency, relative to the engines power. So, if the dash cam’s frequency is close to, but not the same as, the frequency of the light (on the car) then you will notice it flickering on video.

Old filament lights won’t do this, modern LED lights will, the brightness of the light is varied by switching the supply on and off rapidly the on time and off time can be varied, the longer it’s on the brighter the light, this switching happens at something like a thousand times a second, the human eye can’t detect that flicker but the dash cam has a frame rate that, although different from the LED flashing speed, will occasionally syncronise and capture several frames when the LED is off. It won’t capture the same off event but just a series of different ones but it allows you to see the flashing, it is called aliasing, and it happens with digital sampling of many different types of signals.