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

SuperCoug · Aug 15, 2012

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 · Aug 15, 2012

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 · Aug 15, 2012

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 · Aug 15, 2012

Doug_G said:
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 · Aug 15, 2012

Todd Burch said:
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 · Aug 15, 2012

Lloyd said:
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 · Aug 15, 2012

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 · Aug 15, 2012

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 · Aug 15, 2012

JakeP said:
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 · Aug 15, 2012

I had a similar question a few days ago:

Model S Headlight and Tail Light 'beat' frequencies?

chmod a+wrx · Aug 15, 2012

You can also see it very well in this video without the turn signal on. It is a video artifact.

Will The Real Pacific Blue Please Stand Up - Page 3

SuperCoug · Aug 15, 2012

chmod a+wrx said:
You can also see it very well in this video without the turn final on. It is a video artifact.

Will The Real Pacific Blue Please Stand Up - Page 3

Excellent, that seems very definitive.

AndyM · Aug 16, 2012

This is a GREAT design decision. I see Audis all the time that turn the LEDs off when the turn signal is on, and it looks... broken somehow.
Tesla's design choice to dim the LEDs but not turn them off is a nice attention to detail in design, and makes me proud of my choice.

olanmills · Aug 16, 2012

You can see it very clearly here: http://www.youtube.com/watch?v=P5H97zKqRBs, which I mention in the description, though I never knew the reasoning behind it before.

vfx · Aug 17, 2012

We already had this conversation months ago with the tail lights.

Ohms.Law · Aug 17, 2012

Actually I am quite certain that the turning signals, in the front, do indeed pulse in real life. I definately noted it during my DC test drive in the rear view mirror as another test driver was directly behind me. It immediately caught my attention because I've never, ever, seen another car do this. There may indeed may be some pulsating from the video frame rate, but I can attest for sure that what I saw out the rear view mirror was very unique to a turning signal. I even pointed it out to the other occupants (who had a difficult time turning around to see it because of the G forces they were currently experiencing).

FalconNinetyD · Aug 17, 2012

Too bad the turn signal in the T logo on the fender isn't LED. Incandescent bulbs don't belong on a car with this much tech cred.

FalconNinetyD · Aug 17, 2012

Ohms.Law said:
Actually I am quite certain that the turning signals, in the front, do indeed pulse in real life. I definately noted it during my DC test drive in the rear view mirror as another test driver was directly behind me. It immediately caught my attention because I've never, ever, seen another car do this. There may indeed may be some pulsating from the video frame rate, but I can attest for sure that what I saw out the rear view mirror was very unique to a turning signal. I even pointed it out to the other occupants (who had a difficult time turning around to see it because of the G forces they were currently experiencing).

You sure you didn't see this from the HD rear video camera? :biggrin:

Todd Burch · Aug 17, 2012

The D.C. test drive route was the same as the route to my hotel. As I was driving to the hotel after my test drive, there was a Model S about 3 or 4 cars behind me. While turning onto an overpass, I checked the rear view mirror and thought for a minute that the DRLs on one side had died. But come to think of it, it may have been that my glance coincided with one of these pulses, as the Model S would've had its turn signal on. Or, it could've been that the DRL did just indeed die.

William13 · Aug 17, 2012

Fluorescent lights flash at 60 hertz due to AC current in the USA. Incandesant lights also get brighter and dimmer at 60 hertz but not on and off. Cadillac brake lights (LED) flicker at a high frequency. Most people don't notice these things. I have no knowledge of the LED lights on the Tesla. They may also flicker.

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

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