Why LED Lights Pulse and Why It Might Kill You

LED lights are known to cause some strange effects when photographed and filmed. While the banding you might see when photographing LED lights can be irritating, when it comes to cameras on autonomous cars, it might be a matter of life and death.

In this short video, scientist Steve Mould explains how and why LED lights pulse. He then gives an excellent explanation of why this poses a threat to self-driving cars and what can be done to resolve it.

Along with an insight into how LEDs work, there are some intriguing reflections on problem-solving and the evolution of technology. If you're a BMW driver who lives in the U.S., please don't watch if you're easily offended.

If Mould looks vaguely familiar but you’re not sure why, he’s a physicist and stand-up comedian who shot to fame upon discovering what subsequently came to be named the “Mould Effect.” If you want to geek out over self-siphoning beads and their strange behavior, be sure to check out Mould’s very entertaining TED Talk.

Is a global shutter the solution? How else could this problem be solved? Are European indicators better than American turn signals? Leave your thoughts in the comments below.

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Felix C's picture

Great, someone who know nothing about physics, electronics and probably photography.

First, the reason LEDs are pulsed is that they draw an extreme amount of current, especially the old LEDs. In order to save power, they can be turned on for a fraction of the time and to the human eye, they seem on. In some designs, they may be on for 200 milliseconds. During the rest of the time, another set of LEDs can be on. So in a design, if all the LEDs draw 1 amp each, and you had 5 of them, if they were all on, you are drawing 5 amps continually. By sequencing, the LEDs, where only one is on every 200 milliseconds, the the power drawn can be reduced to maybe only 2 amps. It is higher than the 1 amp because in order to give the same preceived brightness, they do have to be driven a little harder.

The second issue where he know nothing about physics, is that he is attempting to record the video using a shutter speed which is not optimal to capture the LED sequencing. He probably adjusted the shutter speed to get the maximum effect, a different shutter speed would have totally mitigated the phenomenon. The car designers who are designing the autonomous vehicles know this are not stupid.

Marcus Joyce's picture

I wanted to record 480 FPS slow Mo on my camera phone. Just then I realized the led lights pulse.

I got out my rotolight and set that up - doesn't pulse.

Also today in a ms teams meeting one of the participants had led lights and they were pulsing too. Quite distracting for 2 hours

Just me's picture

All LED are pulsing, just some professional model goes with higher frequency to avoid this.
Cheap system are pulsing at lower frequencies.

Fristen Lasten's picture

Andy, where do you purchase your stock photos? Lol