Re: LED taillight question

Tegger wrote:
"P.V." <ano@xxxxxxx> wrote in news:tMqal.222$xJ.86@xxxxxxxxxxxxx:

"Don Stauffer" <stauffer@xxxxxxxxxxxx> kirjoitti viestissä news:496a22a0$0$16042$815e3792@xxxxxxxxxxxxxxxxx
Tegger wrote:
Incandescent bulbs have a steady glow. When at night you're behind
cars with incandescent taillights and you make your eyes scan
quickly from one side to the other, the taillights will appear to
leave a solid streak in your field of vision.

I've noticed that there are certain makes of cars with LED
taillights where a quick eye-scan from side to side creates a sort
of "stutter trail" of widely-spaced red dots instead of a streak.
This is obviously due to the fact that LEDs pulse on and off in
operation. But what I don't understand is why it's only certain
models that do this. I've noticed the "stutter" with Cadillacs,
Lincolns, Nissans and VWs, but not with Hondas/Acuras and BMWs.
Honda and BMW LED taillight design makes a nearly solid streak on a
quick eye scan.

Anybody know why the difference?
This is sheer speculation on my part, but the DC on the car
electrical bus is not filtered, it is pretty noisy. LEDs can really
modulate at fairly high frequency. Incandescents do not, because the
thermal inertia of the bulb filters out all except VERY low
frequency. I wonder if we are seeing the noise from the alternator
and regulator, and maybe even hash induced by motors.




But why only on certain makes? Are some manufacturers better able to condition their electrical systems than others?



Here comes my speculation:

I believe they are intentionally modulated to achieve lower-than-full brightness; I've seen rear lights that first appear as "stutter rail"
in the eye, then when the driver applies break the lights go much
brighter and non-stuttering.
So it would seem same lights are used
both as standard rear lights and break lights. I think it'd be better
(or at least nicer to the eye) to just adjust the voltage, but maybe
it's cheaper to the manufacturer to modulate the power.



That was my first thought as well.

I was guessing that the "stutter" ones altered pulse frequency rather than voltage to the LEDs. To wit: foot off the brake, the LED pulses /less/ frequently; foot on the brake, the LED pulses /more/ frequently, the eye perceiving the increased pulse frequency as increased brightness.


I suspect but have no proof that the LEDs in the taillight cluster are wired up so as to provide full brightness when fed a steady 12V (e.g. if a single LED has a voltage drop of 1.3V they wire every 10 of them in series) and then the "dim" (parking light) functionality is provided by PWM.

nate


--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel
.

Relevant Pages

  • Re: LED taillight question
    ... with incandescent taillights and you make your eyes scan quickly from one side to the other, the taillights will appear to leave a solid streak in your field of vision. ... I've noticed that there are certain makes of cars with LED taillights where a quick eye-scan from side to side creates a sort of "stutter trail" of widely-spaced red dots instead of a streak. ... I believe they are intentionally modulated to achieve lower-than-full brightness; I've seen rear lights that first appear as "stutter rail" in the eye, then when the driver applies break the lights go much brighter and non-stuttering. ...
    (rec.autos.tech)
  • Re: Is the hub dynamo headed for an even smaller niche?
    ... No longer with modern LED taillights. ... On-axis, that is true for many LED lights, but off-axis incandescents ... It had several rows of LEDs for brake lights, ... lights so bright as to temporarily blind following drivers. ...
    (rec.bicycles.tech)
  • Re: LED taillight question
    ... quickly from one side to the other, the taillights will appear to ... quick eye scan. ... LEDs can really ... I've seen rear lights that first appear as "stutter rail" ...
    (rec.autos.tech)
  • Re: LED taillight question
    ... with incandescent taillights and you make your eyes scan quickly from one side to the other, the taillights will appear to leave a solid streak in your field of vision. ... Honda and BMW LED taillight design makes a nearly solid streak on a quick eye scan. ... Lighting engineers have found that you can make a LED vehicle light appear much brighter by rapidly switching the LEDs between off and an overdrive state than you can by simply running the LEDS continuously at the maximum rated intensity. ... A higher switching rate "fuses" the image better in your eye than a low switching rate. ...
    (rec.autos.tech)
  • Re: LED taillight question
    ... quickly from one side to the other, the taillights will appear to ... quick eye scan. ... I've seen rear lights that first appear as "stutter rail" ... foot off the brake, the LED pulses /less/ ...
    (rec.autos.tech)