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I wish there was more awareness and concern about LED headlight PWM flicker. PWM (Pulse Width Modulation) is a technique where the power to the output (bulb) i
by mastercheif 4y ago
I wish there was more awareness and concern about LED headlight PWM flicker.
PWM (Pulse Width Modulation) is a technique where the power to the output (bulb) is turned on and off at high frequencies in order to increase efficiency, power handling, and control of the output.
If this on/off switching is done fast enough, your eyes/brain will interpret it as a normal always on light source.
PWM is significantly cheaper and easier to implement vs current source LEDs, so it of course has become dominant in the industry.
When the PWM frequency drops below 120-240hz (cycles a second), some people can start to pick up a strobe like effect from the bulb. This flicker is known to cause additional eye fatigue and can trigger headaches in many.
What's worse is that many aftermarket LED headlights are now using PWM at 60hz. These cheap headlights are often bright blue in order to look modern and impressive. When a car with these installed is behind me at night I have to move my mirror away because the flicker is incredibly distracting and fatiguing.
- Maxburn 4y agoThis is a good point also. Oddly enough it's the LED taillights that get me on this topic. Very easy to notice if you are glancing around.
- Tempest1981 4y agoYes! This drives me crazy. But I mention it to others, (and how to experience it), and their eyes don't perceive it. What % of people are sensitive to this? Any medical documentation? Is NHTSA aware?
- EmilioMartinez 4y agoI usually use my phone's slow motion video to settle the matter. Negotiating where to sit on a restaurant is a prime use case.
- mrguyorama 4y agoJust show them a video. Many cameras pick it up no problem.
- lstodd 4y agoJust about everyone. Wave your hand with fingers spread in front of your eyes and you will see it.
- dang 4y agoCould you please stop posting unsubstantive and/or flamebait comments and otherwise breaking the site guidelines (e.g. https://news.ycombinator.com/item?id=34794878 https://news.ycombinator.com/item?id=34794878)? We ban accounts that do these things, and I don't want to ban you. If you wouldn't mind reviewing https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html and taking the intended spirit of the site more to heart, we'd be grateful. The idea is: if you have a substantive point, make it thoughtfully; if not, please don't comment until you do.
- AceyMan 4y agoWebsearch 'FMVSS 108' for the relevant US regulatory framework.
- Tempest1981 4y agoThanks. I'm scanning it, but it's huge. Does it specify minimum LED refresh rate somewhere? Or is it lacking that today?
- foobiekr 4y agoIt took me awhile to figure out why the LED tail lights made me have a specific weird feeling. If you're old enough, you may have seen the science fiction children's show "Captain Power." The LED tail lights remind me of the target strobe meant to trigger the accompanying toys. Of course if you're old like me, you probably only watched an episode to see what Lightwave3d was capable of, but ..
- JKCalhoun 4y ago> Very easy to notice if you are glancing around. See saccade: https://en.wikipedia.org/wiki/Saccade https://en.wikipedia.org/wiki/Saccade
- SilasX 4y agoWait, what? They are economizing on headlight LED power draw? LEDs are ridiculously efficient to begin with, and a rounding error against a car’s total energy usage. (And in gas cars, get the energy from the battery, which can be recharged off of otherwise-wasted energy from the engine idling.) All on the basis that “lol humans don’t notice the flicker”? Uh, okay, but animals? The 99th percentile humans? Subconscious effects on fatigue (that you mention)? Seems penny-wise and pound-foolish.
- dml2135 4y agoSome people seem to take pride in not noticing subtle visual and auditory effects.
- bob1029 4y agoI envy those people. This world is getting noisier every day.
- schiffern 4y ago>LEDs are... a rounding error against a car’s total energy usage It's more about economizing the power supply package and heatsink integrated within the bulb or lamp assembly.
- klodolph 4y agoYes, this is the real answer. Most LEDs do not operate well at high temperature, unlike incandescent bulbs or HID bulbs (which can both operate inside ovens, if you need them to). A headlight designed for incandescent or HID will not provide enough cooling for LED lamps unless the LED lamps are efficient enough.
- Scoundreller 4y ago> which can be recharged off of otherwise-wasted energy from the engine idling That’s not how it works. When charging, the alternator will put more load on the engine and that will increase fuel input to keep rpm up enough to keep the engine from stalling. Overall, every vehicle designer will seek to minimize any and all loads (even small ones). Worst is when they remove the spare tire, grrrrrr.
- TheAdamist 4y agoThere are no legal aftermarket led headlights anyway. They are all "for offroad use only", which is the biggest scam
- fy20 4y agoIn Europe there are now: https://lumileds.com/austrian-drivers-can-enjoy-road-legal-philips-ultinon-pro6000-h7-and-h4-led/ https://lumileds.com/austrian-drivers-can-enjoy-road-legal-p...
- deleted 4y ago[deleted]
- technothrasher 4y agoThat term comes from EPA regulations about emissions, and led the entire aftermarket industry to figure if they put that on their parts, all was good. (The application here, applied to DOT lighting regulation, is likely bleed over) A few years ago the EPA clarified that when they said “off road use only”, they meant in machines that were never intended to be on a road. So, aftermarket shit designed for a lawnmower, cool. But if you’re designing for a vehicle that was originally designed for the road, you have to stick to EPA regs. This killed a lot of those “off-road use only” disclaimers, but it also panicked the amateur racing community because they tend to use modified road cars. I’m not sure how they worked it out with the EPA, but I don’t hear them complaining any more, so I assume they did.
- westmeal 4y agoThe EPA sent insane fines to tuner shops so nothing was worked out, it's just another cash grab from a useless alphabet agency.
- mitthrowaway2 4y agoEven at fairly high PWM frequencies, strobing can be visible when either the eyes or the source are moving. Which, in a car, they are! You don't need to have exceptional vision. Just glancing from left to right can be enough to leave a confusing and distracting trail of multiple images on your retina.
- debug-desperado 4y agoMotion must explain why I find these LCDs in my home office so offensive. Normally they're not a bother, but when my ceiling fan is on and I look at the lights (below the fan), I swear there is some strobing.
- jnxx 4y agoalso, peripheral vision is more sensitive to movements/flicker than central vision.
- nabilhat 4y agoFord's marker lights are an example of this. The huge consistently illuminated panels are simply amazing. The huge light source is perfect for maximum visibility without presenting a blinding spot source like the majority of automotive lights. But that practically singular investment in automotive optical engineering and innovation is let down by the low frequency PWM driver baling wired into the final design to cut cost by perhaps a dollar or two.
- cosmodisk 4y agoSo is this the reason why my lights inside my home are flashing every time I use slow motion mode on my phone camera?
- sime2009 4y agoIf you have LED lights and they are not at 100% brightness, then yes, most likely.
- datpiff 4y agoThis happens even with cheap non-dimmable lights. If you skimp on filtering in the power supply the LEDs will flicker, but not in a way that's visible to the eye, but very noticeable with a rolling shutter.
- bob1029 4y agoIt is also very obvious to me when you open/close doors or move anything quickly across a contrasting background.
- Wistar 4y agoYes.
- mdp2021 4y agoThere should be «more awareness and concern about LED» in general: even lightbulbs can interfere with electro-medical systems. And one reseller told me - "Well, they should be shielded". Practice far from granted if even the problem is not known.
- jeffbee 4y agoCommercial LED PWM drivers for automotive applications are in the hundreds of kilohertz. If there are aftermarket modules that are only 100 Hz that’s a matter of regulation. It should just be outlawed.
- seszett 4y agoWell I don't know the frequency, but it is easily noticeable to me on most modern cars when moving my eyes. It's definitely not a question of aftermarket modules. The PWM I use at home on an ESP32 is supposed to be in the 1-10 kHz range and I don't see flicker when moving my eyes.
- jeffbee 4y agoYeah, you'd be superman if you thought you could see a khz flicker. I associate flickering headlights with aftermarket because cars with halogen headlights use low-frequency PWM to regulate down high system voltages to 12V. So if you install aftermarket LED kits on those cars you are going to see a PWM of ~90Hz which is awful.
- p1mrx 4y ago> use low-frequency PWM to regulate down high system voltages to 12V That can't be right. Cars are primarily 12VDC.
- jeffbee 4y agoSystem voltage when the engine is running are higher otherwise the 12V battery would never charge. Can be as high as 18V. So cars with halogen lights with just chop it down to 12V. Here's a random video I found demonstrating the phenomenon. https://www.youtube.com/watch?v=82tFav8oGFI https://www.youtube.com/watch?v=82tFav8oGFI
- p1mrx 4y agoInteresting, so they're using PWM to hold the headlights at constant brightness when the alternator runs. Wiring a capacitor in parallel with the headlights should fix that.
- bob1029 4y agoAll of the builder LED lights in my home had this issue. Very expensive to replace these. Newer construction doesn't install proper fixtures anymore. No more user-replaceable bulbs. Everything is screwed directly into the box and you have to do a minor electrical job on every unit you want to replace.
- JKCalhoun 4y agoCuriously, modern lightbulbs for the home use multiple LED elements to achieve their rated brightness. Surely someone can devise an internal circuit to disable some combination of the LEDs to do proper dimming without relying on PWM.
- bob1029 4y agoThe best part: These weren't even dimmable units nor were they on any sort of dimmer-style circuit. On/off only. Still garbage.
- p1mrx 4y agoThen that's not PWM; they cheaped out on the power supply by not including capacitors to smooth out the 60 Hz AC waveform.
- bob1029 4y agoAgreed. I actually considered retrofitting the existing units with parts from digikey. I am 99% sure the issue is due to total absence of any electrolytic capacitors whatsoever on the PCB.
- VLM 4y agoLEDs are a lemon market where the only people making profit are those who ship lemons, everyone else gets pushed out of the market. The luxury days of installing an incandescent bulb that lasts for ten years are gone, lucky to get six months out of "contractor grade" LED products and consumer devices usually don't make it much over a year. Sure, burns a little less coal, but its not like LED manufacture and shipping is as environmentally friendly as beewax candle production LOL. Overall we're probably worse off as a civilization with LED lighting.
- JKCalhoun 4y agoI may be putting too fine a point on it, but I think that even something as perhaps seemingly trivial as being blinded by intense car headlights (these days in the U.S.) is another one of those things that fester in our subconscious building to a creeping sense of dread that the world is not how it should be — that somehow we're living in a modern society that no one would have ever designed, voted for, wished for, desired.
- bob1029 4y ago> somehow we're living in a modern society that no one would have ever designed, voted for, wished for, desired. As mentioned elsewhere in this thread, the majority of the population doesn't seem to notice this crap, at least not in a way that affects their day-to-day happiness. Why not vote for something that sounds good at surface level if you've never perceived that annoying sound or flicker? Why would you even think about it?
- JKCalhoun 4y agoI'm not so sure. So, I'm speaking more generally, but I think many people are aware that things are perhaps not going in the right direction.
- deleted 4y ago[deleted]
- johnaspden 4y agoAs I remember PWM is to control the brightness of the LED. LEDs can only shine at one brightness, they're either on or off, so to dim them to half-brightness you need to have them on half the time, off half the time. That's how you get all the different colours from three LEDs. But they can switch on and off very fast, so if 50Hz is flickery, you can use 500Hz, or 5000Hz. Most microcontrollers have circuitry for this built in, so you just literally write a different constant into the controller. I once made an LED dashboard for use in police cars. After it was rolled out, it was discovered that the flicker frequency was interfering with the radio (the only bug ever found in my code!) My client called me back in to fix it, so I added a zero in the relevant place, and recompiled the code. £400 for about twenty minutes work.
- klodolph 4y ago> LEDs can only shine at one brightness, they're either on or off, This is factually incorrect. LEDs shine at a range of brightnesses. The amount of light emitted is related to the amount of current flowing through the LED, which you are free to control however you want. The cheapest way to do this is to use something like PWM and monitor the average current flowing through the LEDs. However, you can also just use a constant current source, and adjust it to provide the amount of current that you want. I don't know where the idea comes from that LEDs are only on or off. There's no basis in fact here, as far as I can tell.
- kelseyfrog 4y agoThere's an emergent interaction between PWM headlights and rear view mirror cameras(RVMC)[1]. The PWM headlight frequency and RVMCs frame rates are slightly different and phase in and out of each other resulting in a strobing effect. If RVMCs become more popular, eventually an accident will result in the way these two technologies interact. I found it an amusing interaction, but it also has serious safety implications that should be addressed. 1. I'm not sure if there's a better name, but the system where the rear view mirror is a display linked to a camera at the rear of the vehicle in some higher end cars and as an aftermarket addon.
- nabilhat 4y agoThe terrible PWM drivers add another downside - At the frequencies in question the peaks are long enough to increase the retina-stabbing factor much higher than the average brightness, even if they're not long enough to cause noticable strobing. Smoothing capacitors as an aftermarket QOL option is a market that needs to exist. However, poor (or nonexistent) light source shrouding is also a common factor. Bicycle headlights make a great lower-powered example. Cheap bicycle headlights throw much less light than a car headlight but are painfully blinding due to the exposed light source point. Bicycle headlights that meet StVZO regulations shroud the light source, have decent optical design, are far more effective as headlights, and don't make anyones eyes bleed even when they're flashing. Early composite car headlights (post sealed beam) received significant design investment involving established headlight manufacturers and worked extremely well. Auto manufacturers brought headlight design in-house by the time xenon and HID headlights showed up in general use; inexperience and cost avoidance gave those lights an undeserved reputation. A lack of regulatory outcomes rewarded that strategy, leading even established composite headlight quality to decline. Light source shrouds disappeared or became ineffective due to poor reflector design. Headlights on new cars in the US market have declined to the point that they're effectively overpowered cheap bicycle headlights plus extra PWM induced stabbiness, while costing orders of magnitude more as a result of cost cutting. The worst have returned to sealed beam levels of utility, but at least there were aftermarket options to improve sealed beams. Modern aftermarket lights are so bad that it's normal for drivers to install them for malice against other drivers with blinding stock headlights. There really aren't any optically well designed headlights on the US market any more, except for bicycles.