Car LED tail lights strobe rate too slow

Mark wrote:
>
> Anybody else notice that the strobe rate bothers them on the newer cars
> with LED taillights.
>
> At night, when the tail lights are dimmed, (brakes not on) and you
> look at them and blink or turn your head, the after image is very
> strange, you see dashes of light. I find it very annoying and
> distracting and I hope that this problem is recognized and corrected
> before every car on the road is like this.

That's interesting. I wonder what frequency they use to PWM the LED
arrays.

The instrument cluster dimming in my Toyota runs at 400 Hz.

--
Paul Hovnanian
------------------------------------------------------------------
How do I set a laser printer to stun?

"Paul Hovnanian P.E." wrote:
>
> Mark wrote:
> >
> > Anybody else notice that the strobe rate bothers them on the newer cars
> > with LED taillights.
> >
> > At night, when the tail lights are dimmed, (brakes not on) and you
> > look at them and blink or turn your head, the after image is very
> > strange, you see dashes of light. I find it very annoying and
> > distracting and I hope that this problem is recognized and corrected
> > before every car on the road is like this.
>
> That's interesting. I wonder what frequency they use to PWM the LED
> arrays.
>
> The instrument cluster dimming in my Toyota runs at 400 Hz.
>
> --
> Paul Hovnanian


Hmmm Learn something every day; did not know that these arrays use PWM.

I haven't noticed tail light flicker, but then I drive very little (bicycle, and
rarely in traffic). Am driving to VT for the 4th and will certainly watch out
for flicker (a welcome "project", against going bonkers during the 7-hr, solo
drive).

I'd think just about any PWM freq. could be problematic. Also, I am thinking
about a dual strobe effect, one caused by resonances w/i my vehicle, the other
caused by resonances w/i the LED vehicle. Imagine the combined effect of very
rough road *plus* harmonic motion of LED fixtures. I think I'm gonna throw up.

--
Michael

Paul Hovnanian P.E. wrote:
> Mark wrote:
> >
> > Anybody else notice that the strobe rate bothers them on the newer cars
> > with LED taillights.
> >
> > At night, when the tail lights are dimmed, (brakes not on) and you
> > look at them and blink or turn your head, the after image is very
> > strange, you see dashes of light. I find it very annoying and
> > distracting and I hope that this problem is recognized and corrected
> > before every car on the road is like this.
>
> That's interesting. I wonder what frequency they use to PWM the LED
> arrays.
>
> The instrument cluster dimming in my Toyota runs at 400 Hz.
>
> --
> Paul Hovnanian
> ------------------------------------------------------------------
> How do I set a laser printer to stun?

LEDs only light up at 'one' brightness level, so to make 'em dim it has
to be a brief pulse followed by a long seperation before the next
pulse.

Comparing the pulsing to 120Hz, it looks to be a good bit below that.

Bugs me a little too.

Dave

In message .com>,
writes
>LEDs only light up at 'one' brightness level, so to make 'em dim it has
>to be a brief pulse followed by a long seperation before the next
>pulse.
>
>Comparing the pulsing to 120Hz, it looks to be a good bit below that.
>
>Bugs me a little too.

Yep. It's a very noticeable flicker. I wonder if it's a standard
automotive chip.

--
Clive Mitchell
http://www.bigclive.com

wrote:

> Paul Hovnanian P.E. wrote:
>
>>Mark wrote:
>>
>>>Anybody else notice that the strobe rate bothers them on the newer cars
>>>with LED taillights.
>>>
>>>At night, when the tail lights are dimmed, (brakes not on) and you
>>>look at them and blink or turn your head, the after image is very
>>>strange, you see dashes of light. I find it very annoying and
>>>distracting and I hope that this problem is recognized and corrected
>>>before every car on the road is like this.
>>
>>That's interesting. I wonder what frequency they use to PWM the LED
>>arrays.
>>
>>The instrument cluster dimming in my Toyota runs at 400 Hz.
>>
>>--
>>Paul Hovnanian
>>------------------------------------------------------------------
>>How do I set a laser printer to stun?
>
>
> LEDs only light up at 'one' brightness level, so to make 'em dim it has
> to be a brief pulse followed by a long seperation before the next
> pulse.
>
> Comparing the pulsing to 120Hz, it looks to be a good bit below that.
>
> Bugs me a little too.
>
> Dave

PWM frequencies are determined by the lamp manufacturer, but most I've
seen are on the order of 500 Hz - well above what is considered the
flicker threshold. You shouldn't be seeing the "strobing", but since
you are I would suggest filing a report with NHTSA Office of Defects
Investigation (www-odi.nhtsa.dot.gov/ivoq). If enough people complain,
then they can make a ruling that requires manufacturers to have a
minimum PWM frequency. Make sure you include specific vehicle
information (Make, Manufacturer, etc.).

As an aside - do you see this with the LED lamps that have been in use
on trucks for the past 5 years? They use the same technology. Try the
newer FedEx delivery trucks.

--
Douglas Cummins
Calcoast - ITL

wrote:
> Paul Hovnanian P.E. wrote:
> > Mark wrote:
> > >
> > > Anybody else notice that the strobe rate bothers them on the newer cars
> > > with LED taillights.
>
> LEDs only light up at 'one' brightness level, so to make 'em dim it has
> to be a brief pulse followed by a long seperation before the next
> pulse.
>
> Comparing the pulsing to 120Hz, it looks to be a good bit below that.
>

Well, no, you can have the LED produce any amount of light, between
none and its maximum, by varying the amount of current flowing through
it. Of course this requires dropping the rest of your supply voltage
across some other circuit element and so will use more power. But I
think the real reason that auto manufacturers use PWM is that
transistors for just on-off switching are cheap.

To join the chorus, I find them annoying also and really wish they
would use a higher frequency.

--
-Harold Hill

wrote:
>
> wrote:
> > Paul Hovnanian P.E. wrote:
> > > Mark wrote:
> > > >
> > > > Anybody else notice that the strobe rate bothers them on the newer cars
> > > > with LED taillights.
> >
> > LEDs only light up at 'one' brightness level, so to make 'em dim it has
> > to be a brief pulse followed by a long seperation before the next
> > pulse.
> >
> > Comparing the pulsing to 120Hz, it looks to be a good bit below that.
> >
>
> Well, no, you can have the LED produce any amount of light, between
> none and its maximum, by varying the amount of current flowing through
> it. Of course this requires dropping the rest of your supply voltage
> across some other circuit element and so will use more power. But I
> think the real reason that auto manufacturers use PWM is that
> transistors for just on-off switching are cheap.
>
> To join the chorus, I find them annoying also and really wish they
> would use a higher frequency.
>
> --
> -Harold Hill

PWM is used in order to exceed the maximum continuous output available
from the LED. LEDs can be overdriven past their continuous operating
currents and generate higher peak light outputs (within some limits) by
operating them at a reduced duty cycle to hold the average current and
therefore chip heating within the continuous operating limits.

Pete C.

Paul Hovnanian P.E. wrote:
> Mark wrote:
> >
> > Anybody else notice that the strobe rate bothers them on the newer cars
> > with LED taillights.
> >
> > At night, when the tail lights are dimmed, (brakes not on) and you
> > look at them and blink or turn your head, the after image is very
> > strange, you see dashes of light.

I've never experienced that. Do you wear glasses or contacts?


> I find it very annoying and
> > distracting and I hope that this problem is recognized and corrected
> > before every car on the road is like this.

I'n not sure there is a problem to be corrected.


>
> That's interesting. I wonder what frequency they use to PWM the LED
> arrays.
>
> The instrument cluster dimming in my Toyota runs at 400 Hz.
>
> --
> Paul Hovnanian
> ------------------------------------------------------------------
> How do I set a laser printer to stun?

In article >, "Pete C." > wrote:
wrote:
>>
>> wrote:
>> > Paul Hovnanian P.E. wrote:
>> > > Mark wrote:
>> > > >
>> > > > Anybody else notice that the strobe rate bothers them on the newer cars
>> > > > with LED taillights.
>> >
>> > LEDs only light up at 'one' brightness level, so to make 'em dim it has
>> > to be a brief pulse followed by a long seperation before the next
>> > pulse.
>> >
>> > Comparing the pulsing to 120Hz, it looks to be a good bit below that.
>> >
>>
>> Well, no, you can have the LED produce any amount of light, between
>> none and its maximum, by varying the amount of current flowing through
>> it. Of course this requires dropping the rest of your supply voltage
>> across some other circuit element and so will use more power. But I
>> think the real reason that auto manufacturers use PWM is that
>> transistors for just on-off switching are cheap.
>>
>> To join the chorus, I find them annoying also and really wish they
>> would use a higher frequency.
>>
>> --
>> -Harold Hill
>
>PWM is used in order to exceed the maximum continuous output available

I just hope I don't wreck on the way home tonight. Now I have to look at the Led's more
than I'm allready doing.

I just wished they would mandate being able to see both left and right front turn signals
on vehicles like they used to. Putting them on the side mirrors in front, would solve that problem.
When I see a stopped vehicle and don't see their turn signals, I don't give them any slack. To me
they are there and don't know what their doing, but I have to still watch out in case
they shoot out in front of me.


greg

On Wed, 28 Jun 2006 18:08:13 GMT, "Pete C."
> wrote:

wrote:
>>
>> wrote:
>> > Paul Hovnanian P.E. wrote:
>> > > Mark wrote:
>> > > >
>> > > > Anybody else notice that the strobe rate bothers them on the newer cars
>> > > > with LED taillights.
>> >
>> > LEDs only light up at 'one' brightness level, so to make 'em dim it has
>> > to be a brief pulse followed by a long seperation before the next
>> > pulse.
>> >
>> > Comparing the pulsing to 120Hz, it looks to be a good bit below that.
>> >
>>
>> Well, no, you can have the LED produce any amount of light, between
>> none and its maximum, by varying the amount of current flowing through
>> it. Of course this requires dropping the rest of your supply voltage
>> across some other circuit element and so will use more power. But I
>> think the real reason that auto manufacturers use PWM is that
>> transistors for just on-off switching are cheap.
>>
>> To join the chorus, I find them annoying also and really wish they
>> would use a higher frequency.
>>
>> --
>> -Harold Hill
>
>PWM is used in order to exceed the maximum continuous output available
>from the LED. LEDs can be overdriven past their continuous operating
>currents and generate higher peak light outputs (within some limits) by
>operating them at a reduced duty cycle to hold the average current and
>therefore chip heating within the continuous operating limits.
>
>Pete C.

What you describe works only if the LEDs are being flashed
slower than the flicker fusion frequency, which is not the
case here. And even then, only the pulse output is higher
than the maximum continuous rated output. The average
output is not.

These LEDs are being pulsed fast enough that the eye-brain
system sees the average light output while the LED chip
temperature responds to the average power. I don't see how
there is any increase in available output due to pulsing.

The strobe effect that people are complaining about could be
eliminated by filtering the power delivered to the LED after
the PWM control circuit.

--
Vic Roberts
http://www.RobertsResearchInc.com
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