Do white LED lights strobe when turn signals are on? Video appears to say "Yes"

[SuperCoug]

I was looking at some video clips that I shot at the Seattle stop of the Get Amped Tour and I noticed something strange as one of the cars pulled up to the curb. There is a rapid strobe that can be seen on the while LED lights on the same side of the car as the active turn signal. Look at the car that pulls up to the curb and you'll see what I'm talking about (especially when the car pulls into the shadows).

http://www.youtube.com/watch?v=xD7_I3KqQNI&feature=plcp

http://www.youtube.com/watch?v=xD7_I3KqQNI&feature=plcp

[Todd Burch]

Interesting. At first I thought you were talking about rapid pulsing of LEDs to modify their brightness, but that doesn't look like this. Come to think of it, I don't think I've ever seen the front with the turn signal on, so it could very well be. Thats a nice way to help attract attention to a turn signal for oncoming traffic.

[Doug_G]

It's aliasing caused by the Pulse-Width Modulation of the LEDs (used to control their brightness) interacting with the frame rate of the video camera. The human eye can't see the pulses, but it appears in videos courtesy of the same effect that makes wagon wheels turn backwards in western movies.

[Todd Burch]

It's aliasing caused by the Pulse-Width Modulation of the LEDs (used to control their brightness) interacting with the frame rate of the video camera. The human eye can't see the pulses, but it appears in videos courtesy of the same effect that makes wagon wheels turn backwards in western movies.

Interesting that the pulsing coincidentally stopped when the turn signal was turned off.

[Lloyd]

Interesting that the pulsing coincidentally stopped when the turn signal was turned off.

Or possibly when the car went back into the sunlight and the daylight running LED did not need to be dimmed anymore?

[pxy]

Or possibly when the car went back into the sunlight and the daylight running LED did not need to be dimmed anymore?

^This. When the DRL's are on, it looks like one side is dimmed with the turn signal, so going back to the PWM comment, it is not visible by eye. I think other manufactures just turn the one side off until the signal is off.

[JakeP]

I asked about this in Chicago, and Chris from Oak Brook indicated it was the frame-rate issue in the video that Doug_G mentions above. We stood there and watched while the turn signal was activated right in front of us, and there was no pulsing (this was on the Silver non-Perf).

[TEG]

Maybe it had something to do with the effective shutter speed of the digital camera?
For instance, when the running light went into the shadow of the flag, maybe the camera changed the effective "shutter speed" for that "zone" of the image it was capturing? I agree with Doug_G on the likelyhood it is interaction between LED strobing and camera shutter. (Like a beat frequency of light.)

Modern digital cameras are quite "smart" these days, and do things to try to compensate for varying lighting conditions.

[Lloyd]

I asked about this in Chicago, and Chris from Oak Brook indicated it was the frame-rate issue in the video that Doug_G mentions above. We stood there and watched while the turn signal was activated right in front of us, and there was no pulsing (this was on the Silver non-Perf).

Your eyes can't percieve the pulsing however.

[stephenpace]

I had a similar question a few days ago:

Model S Headlight and Tail Light 'beat' frequencies?