Car LED lights flicker

LuisM

Registered User
Yep. They do. Here's a proof.

IMG_3809_gir_rec.jpg


This is a picture of the A3 8V daytime LED lights, taken at 1/50 s shutter speed, without image stabilization. The catch is, the camera was moving vertically. You see five instances of the daytime light strip, which indicates that LED turns on and off about 50*5 = 250 times per second, or 250 Hz.

By the way, the yellowish fog lights below show the LED lights a continuous vertical displacement in the picture, instead of several distinct positions. They are standard lamps, not LEDS. So no flicker.

Some people notice this flickering with their naked eyes. Most seem not to. I'm among the "lucky" ones who notice it. If that's not your case, don't be sad. It's not particularly nice to see lights flickering all over the place.

Yes, all over the place. Because it's not only head lights. The car's interior lights, speedometer, even the circular lights of the glass containers below the climate controls: they all flicker. The following two pictures illustrate this. They were taken with 1/25 shutter speed. If you count the number of instances of each light or mark in the speedometer, you can see
  • 8 instances for the circular lights under the climate control buttons. This number applies also for upper lights, and for the button that turns on the emergency lights (all-blinkers); although they are not shown in this picture. So their flicker frequency is 200 Hz.
  • Speedometer, RPM-meter: 10 instances. So they flicker at 250 Hz. Note, however, that whereas numbers and outer marks do flicker, indicator lights for EPC or safety belt don't: they leave a continuous trace.
  • The DIS flickers faster. The horizontal line right under the car plot appears 24 times in the picture. So 24*25 = 600 Hz. This was a surprise for me, as I don't notice the DIS flickering with the naked eye. So now I know that the threshold above which I don't perceive the flickering is between 250 Hz and 600 Hz.
IMG_3828_rec_proc.jpg


IMG_3832.jpg


Tail light LED lights, on the contary, don't flicker in the A3 8V. (They do flicker in other cars. Main offender for me is the Peugeot 307 cc. Their tail lights are really annoying. I hate to drive behind one of those at night.) As the picture below shows, the tail lights produce a continuous band when the camera is moved vertically. Shutter speed is 1/100 s, so even frequencies as high as 1000 Hz should have been detected (the tail light would have been seen at 10 distinct positions). By the way, the dimmer light in the lower right corner is just a reflection.

IMG_3817_gir_rec.jpg


Do you perceive this flickering in LED lights? Do you find it annoying? It is for me, and for other people too. But I guess it's not many of us who do notice it, otherwise there would be more complaints, and car makers would rise flicker frequency so it wouldn't be annoying anymore. In my case, for example, 600 Hz (as in the DIS) is already unnoticeable.
 
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mjcourtney

Registered User
Dimming LEDs is usually achieved by pulsing them, so that you reduce the time that they are emitting light (scan rate). You'll notice it more the dimmer you set the cabin lights. Slower than 60hz and most people will start to see the flickering. Sounds like you have well tuned eyes if you can see it! (I can't).

You can also see it sometimes by moving your head or scanning your eyes across the light, and you'll perceive a 'flicker'. If you can't see the rear lights flickering then I suspect they've used dimmer LEDs that don't require scanning, eg they're on 100%.
 

LuisM

Registered User
Actually, those "well" tuned eyes are a source of annoyance with so much flickering :)

Yes, the effect is most noticeable when you look away from the light. I can then actually see the light at several places, just like in the photographs.


Dimming LEDs is usually achieved by pulsing them, so that you reduce the time that they are emitting light (scan rate). You'll notice it more the dimmer you set the cabin lights. Slower than 60hz and most people will start to see the flickering. Sounds like you have well tuned eyes if you can see it! (I can't).

You can also see it sometimes by moving your head or scanning your eyes across the light, and you'll perceive a 'flicker'. If you can't see the rear lights flickering then I suspect they've used dimmer LEDs that don't require scanning, eg they're on 100%.
 

veeeight

I am a very pretty girl
VCDS Map User
All the dimmable LEDs in the interior cabin of the car are PWM driven.

For the speedo and Rev counter illumination, try turning the brightness dial up to the maximum, can you still see the flicker?
 

LuisM

Registered User
In my first days with the car I did some tests and I found the illumination was annoying too when set to maximum brightness. Not sure if it was because of flickering or just because the light was too intense. I'll do some tests to see if I notice flickering in that situation. Thanks for the suggestion!

Anyway, someone told me one of the reasons to switch on and off the LEDs is that if you feed the diodes with a continuous voltage they get burnt. If that's correct, I guess even when set at full brightness there will be some off time in each period.

All the dimmable LEDs in the interior cabin of the car are PWM driven.

For the speedo and Rev counter illumination, try turning the brightness dial up to the maximum, can you still see the flicker?
 
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