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Comment by gruez | Hacker News Reader

>strobing

I've never seen a strobing tail light. The most "strobing" I've seen are some brake/tail lights that flash for 1-2 seconds right after they're turned on (to alert drivers better? still annoying imo).

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Almost all LED taillights strobe, but too fast for most people to see the strobing due to persistence of vision. But if you move your eyes side to side while taillights are in your field of view you can catch a glimpse of the strobing.

That blinking is usually a dealer installed add-on that can be hard to get removed (and usually involves modifying the factory wiring, thanks), generally on the high mount brake light (CHMSL). I personally believe these lights violate the law (and I think this letter supports that position [1], if it's still current?), but dealers gonna deal.

But I think the poster is complaining about the higher frequency flickering that's supposed to be imperceptible... if you don't perceive it, that's better for you. Unfortunately, I regularly see it especially when moving my heads or eyes and find it pretty distracting. There's circuit design techniques to reduce the flickering, but saving pennies here and there adds up, so there you go.

[1] https://www.nhtsa.gov/interpretations/20288ztv

I doubt this even saves pennies. These lights are driven by an IC, and the current is regulated because the supply voltage is nowhere near stable enough to get away with an unregulated drive circuit. The mention of the TLE4242 chip upthread quite clearly indicates that there’s an entire wire from the ECU to the driver to control it. All that’s needed is for the IC to support some way to change the current regulator set point instead of flashing the LED. Sure, this would add a handful of transistors and maybe a capacitor or two inside the IC, and it will cost some R&D, but it won’t affect the unit cost in any meaningful way.

(This could be as simple as a filter that turns the duty cycle into a current target. This feature is nearly ubiquitous in off-the-shelf “dimmable constant current” line-voltage-input LED drivers from basically every supplier (e.g. Mean Well). The tricky bit would be to get the thing to turn on quickly enough without annoying brightness swings, so some actual care in the filter design and frequency selection would be required. Or one could use 0-10V control (also ubiquitous) or have just two states plus off or have digital control… there’s no shortage of perfectly fine solutions.)

https://en.wikipedia.org/wiki/Stroboscopic_effect . See the "Root Causes" and "Mitigation" sections for a discussion of LEDs.

Also: https://standards.ieee.org/ieee/1789/4479/

For me, it's the sudden sensation of being mashed in a Berlin disco. While driving!

I know some cars have the blinking when you are applying sudden pressure to the brakes. To alert people behind them they may be stopping quickly. People use their hazards in some states for the same reason.

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