PWM for car headlights?!
- Thread starter N8N
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Re: Current best 6" x 8" sealed beam replacements
Pulsewidth modulation (PWM) feed for the headlamps and other exterior lights is increasingly common. It ensures the bulbs receive the intended/design voltage, allows soft startup, and filters out line spikes. All of which means the lights provide the intended output over the longest possible lifespan between bulb changes. It also permits neat tricks like using a single-filament bulb for both a bright and a dim function, such as stop/tail or turn/park, instead of a 2-filament bulb. Doing it with one filament and PWM means faster rise time for the brake lights, a safety advantage.
Pulsewidth modulation (PWM) feed for the headlamps and other exterior lights is increasingly common. It ensures the bulbs receive the intended/design voltage, allows soft startup, and filters out line spikes. All of which means the lights provide the intended output over the longest possible lifespan between bulb changes. It also permits neat tricks like using a single-filament bulb for both a bright and a dim function, such as stop/tail or turn/park, instead of a 2-filament bulb. Doing it with one filament and PWM means faster rise time for the brake lights, a safety advantage.
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Re: Current best 6" x 8" sealed beam replacements
I get that, I know what PWM is, but I just don't understand why one would be artificially reducing the voltage to the *headlights* of all things. I'm happy to accept the reduced life so long as the lights are being driven at a full 14V or whatever the system voltage is. (that's assuming halogens, of course, it makes no difference using ballasted HIDs or driver-regulated LEDs.)
Or are the new Heeps doing something odd like using a nominal 14V or 16V electrical system? I hadn't heard about that but it would make sense if they were; but I haven't heard of anything other than the classic 6-cell lead-acid, AGM, or spiral-cell batteries being used in *any* new vehicles save for hybrids or electrics. (then again, new cars don't interest me as much as they used to, since I'm no longer a kid and never actually buy new cars...)
I get that, I know what PWM is, but I just don't understand why one would be artificially reducing the voltage to the *headlights* of all things. I'm happy to accept the reduced life so long as the lights are being driven at a full 14V or whatever the system voltage is. (that's assuming halogens, of course, it makes no difference using ballasted HIDs or driver-regulated LEDs.)
Or are the new Heeps doing something odd like using a nominal 14V or 16V electrical system? I hadn't heard about that but it would make sense if they were; but I haven't heard of anything other than the classic 6-cell lead-acid, AGM, or spiral-cell batteries being used in *any* new vehicles save for hybrids or electrics. (then again, new cars don't interest me as much as they used to, since I'm no longer a kid and never actually buy new cars...)
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First: the nominal "12 volt" auto electrical system has never actually been 12.0 volts, nor has it ever been the 12.6 volts of a fully-charged "12 volt" battery. System voltage is always higher than that when the engine is running, because otherwise the battery would not charge. For many years the range of system voltage was about 13.5 to 14.5 depending on battery state of charge and ambient temperature (system voltage must be higher to charge a colder battery, lower to avoid boiling a hotter battery). But system voltage has been creeping upward, more on some makers' vehicles than others. A relevant example is the brake/signal light bulbs GM released, 4114K (clear) and 5702KA (amber) to replace 3157/4157 clear and amber bulbs. The difference is the GM bulbs are rated at 14v instead of at 12.8v; this was GM's fix for a NHTSA preliminary investigation into short brake light bulb life and customer complaints about short DRL bulb life. GM charging system voltage has long tended to be a little higher than some other makers; some GM voltage regulators are calibrated to 15.4 volts! This is still, however, considered a "12 volt" system.
One would be regulating the voltage to the headlamps because it's a good way of making sure they receive the intended voltage and so produce the intended amounts of light over the intended lifespan. The whole system of regulation, design, and certification in the US is based on 12.8v to the lamps. In the past there was no good, cost-effective way to closely control voltage to the headlamps. The best that could be done was to build in a certain amount of voltage drop into the wiring (at least one manufacturer actually issued a TSB and service parts package to put more resistance into the headlamp circuit because too many owners were complaining about short bulb life). But this is a crude method; the lamps can still be hit with transient surges and spikes, and their operating voltage still varies depending on whole-system voltage.
Sure, voltage higher than the design voltage means more light for the driver to see farther. But it also means more foreground light, and it also means more glare light. There are maximum limits on both of those categories of light from headlamps, for very sound safety reasons: too much foreground light severely degrades the driver's distance vision, and too much glare light adversely affects other drivers' comfort and ability to see. The glare limits for headlamps are specified at 12.8v, and you (personally, N8N, from other posts you've made in this forum) think they're too high. One of the effects of closer adherence to design voltage, for example by feeding headlamps with PWM, is less glare from US headlamps. At the same time, headlamp safety performance (how well they let the driver see) generally tends to increase over time as technology improves. That means headlamps are getting better both in terms of driver vision and glare control, in part due to more precise control of operating voltage. I can't imagine a good argument against that.
Voltage higher than the design voltage also means severely shortened bulb lifespan. Filament bulbs' light output varies to the power 3.4 with voltage input, but lifespan varies to the power -13 with voltage input. Take a bulb rated for 1000 lumens and 1000 hours at 12.8v, and operate this bulb at 14.4v. Now it produces 1493 lumens (an increase of 49%) and lasts for 216 hours (a decrease of 78%).
From the automaker's perspective, this is all a complete dealbreaker. It means the headlamp's performance is very likely no longer compliant with the legal requirements as far as light distribution goes, and it means bulb burnouts about 5x more often, which not only means increased warranty costs but also damage to the reputation of the vehicle as a quality product.
Individual drivers deciding whether/how to modify their vehicles may very well be able to justify disregarding bulb lifespan in their quest for more seeing light, especially if they are using headlamps that by design produce very little glare on low beam.
One would be regulating the voltage to the headlamps because it's a good way of making sure they receive the intended voltage and so produce the intended amounts of light over the intended lifespan. The whole system of regulation, design, and certification in the US is based on 12.8v to the lamps. In the past there was no good, cost-effective way to closely control voltage to the headlamps. The best that could be done was to build in a certain amount of voltage drop into the wiring (at least one manufacturer actually issued a TSB and service parts package to put more resistance into the headlamp circuit because too many owners were complaining about short bulb life). But this is a crude method; the lamps can still be hit with transient surges and spikes, and their operating voltage still varies depending on whole-system voltage.
Sure, voltage higher than the design voltage means more light for the driver to see farther. But it also means more foreground light, and it also means more glare light. There are maximum limits on both of those categories of light from headlamps, for very sound safety reasons: too much foreground light severely degrades the driver's distance vision, and too much glare light adversely affects other drivers' comfort and ability to see. The glare limits for headlamps are specified at 12.8v, and you (personally, N8N, from other posts you've made in this forum) think they're too high. One of the effects of closer adherence to design voltage, for example by feeding headlamps with PWM, is less glare from US headlamps. At the same time, headlamp safety performance (how well they let the driver see) generally tends to increase over time as technology improves. That means headlamps are getting better both in terms of driver vision and glare control, in part due to more precise control of operating voltage. I can't imagine a good argument against that.
Voltage higher than the design voltage also means severely shortened bulb lifespan. Filament bulbs' light output varies to the power 3.4 with voltage input, but lifespan varies to the power -13 with voltage input. Take a bulb rated for 1000 lumens and 1000 hours at 12.8v, and operate this bulb at 14.4v. Now it produces 1493 lumens (an increase of 49%) and lasts for 216 hours (a decrease of 78%).
From the automaker's perspective, this is all a complete dealbreaker. It means the headlamp's performance is very likely no longer compliant with the legal requirements as far as light distribution goes, and it means bulb burnouts about 5x more often, which not only means increased warranty costs but also damage to the reputation of the vehicle as a quality product.
Individual drivers deciding whether/how to modify their vehicles may very well be able to justify disregarding bulb lifespan in their quest for more seeing light, especially if they are using headlamps that by design produce very little glare on low beam.
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And there you have it. I'd be happy to pay more for lights that are designed to just barely squeak under the legal output limits if designed with a proper beam pattern and I'll also be happy to replace the bulbs more often if I have to (assuming that the vehicle isn't so asininely designed that it's a 45 minute job; unfortunately there are a few out there. I'm looking at you, Chevy.) This is also why I'm rather partial to vehicles that stick with sealed beam format lights, as I can keep the same vehicle and upgrade it rather than being stuck with whatever the factory delivers, as not all good cars come with good headlights. Unfortunately it seems that the general public just cares about passing their annual safety inspection... and I can say this from experience, having actually spent (wasted) too much time trying to convince people to fix things that really need to be fixed on their vehicles... sometimes you just have to shrug it off and tell yourself that you did everything that you were supposed to do and if they're too cheap to save themselves having to buy a new car later, it's their choice.
But there are a sizeable number of exceptions, as evidenced by the people who just aren't happy with the headlights on their JKs... I think that I've seen more discussions of the new LED options over on jeepforum than I have here (of course, that may be because it's also one of those applications that isn't quite plug 'n' play, due to the PWM not only on DRL but also on low and high beam.)
I'm assuming that since I haven't seen mention of it being done that it's not possible to adjust the voltage delivered to the headlights in normal operation through software hacks?
That's another thing: packaging constraints continue to get tighter and tighter, pressed by simultaneous demands for lower fuel consumption and emissions, increased passenger space, and improved pedestrian protection (among other factors). There are many vehicles with very difficult, therefore very costly headlight bulb service access. That, in turn, puts an even higher priority on bulb lifespan (actually it means manufacturers should be installing HID or LED headlamps, but the cost premium means there's still a lot of halogen marketshare).
The stock Jeep Wrangler headlamp is not very nice to drive with, despite its reasonably decent objective performance. It could have been much better than it is (or worse!) with some different design choices.
I've heard of software config changes on some vehicles (VW products, mostly) to adjust the intensity of certain exterior lighting functions, but I don't recall ever hearing of such a thing for the low and high beam headlamp functions on any make of vehicle.
The stock Jeep Wrangler headlamp is not very nice to drive with, despite its reasonably decent objective performance. It could have been much better than it is (or worse!) with some different design choices.
I've heard of software config changes on some vehicles (VW products, mostly) to adjust the intensity of certain exterior lighting functions, but I don't recall ever hearing of such a thing for the low and high beam headlamp functions on any make of vehicle.
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Re: Current best 6" x 8" sealed beam replacements
Very interesting. I have a JK and read a lot about how others upgrade their lighting.
Many bypass the PWM feed with a dedicated harness (Sterns/SMS). Does the increase in voltage to the bulbs (at the cost of lifespan) also expose the bulbs to line spikes, hard (?) startup, or other undesirable effects the PWM feed prevented?
(noob question, just joined forum, I promise to use the search feature extensively!):whistle:
Very interesting. I have a JK and read a lot about how others upgrade their lighting.
Many bypass the PWM feed with a dedicated harness (Sterns/SMS). Does the increase in voltage to the bulbs (at the cost of lifespan) also expose the bulbs to line spikes, hard (?) startup, or other undesirable effects the PWM feed prevented?
(noob question, just joined forum, I promise to use the search feature extensively!):whistle:
Re: Current best 6" x 8" sealed beam replacements
I see on the other "current best 6X8" thread you mentioned the Jeep JK H13 headlamps. I hate to hijack a thread but could use some advice on that very subject.
I thought I did an upgrade a few years ago when I converted the H13 to H4 with a pigtail and IPF lenses but I've since learned better than to trust my eyes or marketing hype. The latest tech (trucklites, JWS, Bixenon, etc.) is out of the budget this year (need 5 new tires soon!) so I'm stuck firmly well behind the cutting edge.
But I've been given a fairly new SMS wiring harness for H4 lamps (my friend sold his cibies and bulbs but had the harness leftover).
So having the SMS wiring harness and some phillips 9003 xps2 bulbs in hand and the desire to be safe, legal, affordable, and well-lit, is my best move to ditch the 7" round IPF 920H4 lenses and buy some 7" cibies?
Or install the harness and live with the lenses until I can afford to join the trucklite/JWS echelon? (I'm worried the lenses aren't very good and the extra power will make them worse)
or leave well enough alone and just stay home after dark....?
Thanks for the welcome! It's all kind of perplexing. I've read up as much as I can lately, even caught up on Hilldweller's shootout that grew about 50X longer than when I originally read through it a couple years ago.
I see on the other "current best 6X8" thread you mentioned the Jeep JK H13 headlamps. I hate to hijack a thread but could use some advice on that very subject.
I thought I did an upgrade a few years ago when I converted the H13 to H4 with a pigtail and IPF lenses but I've since learned better than to trust my eyes or marketing hype. The latest tech (trucklites, JWS, Bixenon, etc.) is out of the budget this year (need 5 new tires soon!) so I'm stuck firmly well behind the cutting edge.
But I've been given a fairly new SMS wiring harness for H4 lamps (my friend sold his cibies and bulbs but had the harness leftover).
So having the SMS wiring harness and some phillips 9003 xps2 bulbs in hand and the desire to be safe, legal, affordable, and well-lit, is my best move to ditch the 7" round IPF 920H4 lenses and buy some 7" cibies?
Or install the harness and live with the lenses until I can afford to join the trucklite/JWS echelon? (I'm worried the lenses aren't very good and the extra power will make them worse)
or leave well enough alone and just stay home after dark....?
Alaric Darconville
Flashlight Enthusiast
Re: Current best 6" x 8" sealed beam replacements
If you still have the factory headlamps, put 'em back in and get them aimed. (In effect, undoing the PIAA *downgrade*.)
If you still have the factory headlamps, put 'em back in and get them aimed. (In effect, undoing the PIAA *downgrade*.)
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Re: Current best 6" x 8" sealed beam replacements
Yes -- those IPF units don't actually (technically/legally) qualify as headlamps. I'm not being hyperbolic here, it's really true: they are not designed to conform, nor tested or certified/approved, to any technical standard for headlamps.
If you're using the standard-wattage bulbs (the Philips 9003XP is a very good one) I'd leave out the harness and continue using the pigtails, thus keeping the bulb life benefits of the PWM feed.
Very important: aim the lamps correctly.
Yes -- those IPF units don't actually (technically/legally) qualify as headlamps. I'm not being hyperbolic here, it's really true: they are not designed to conform, nor tested or certified/approved, to any technical standard for headlamps.
If you're using the standard-wattage bulbs (the Philips 9003XP is a very good one) I'd leave out the harness and continue using the pigtails, thus keeping the bulb life benefits of the PWM feed.
Very important: aim the lamps correctly.
Alaric Darconville
Flashlight Enthusiast
I must have only *thought* I submitted the post-- my recommendation, instead of spending more money, is to revert to the factory headlamps (if you still have them) and get them aimed properly. Undoing the downgrade to IPF lamps rather than buying yet another set of lamps may make more sense for now.
Guess it's a good thing I messed up-- for some reason I was laboring under the impression that you had PIAA "headlamps". (Would not IPF, by any other name, be just as junky?)
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Alaric Darconville
Flashlight Enthusiast
Oh, c'mon, you know they don't make headlamps at all-- at least not for use on ANY road :)
Thank you, both. I'll look for the factory lamps but I suspect they are long gone (we moved). If they don't turn up, I'll contact DS about the Cibie H4.
Then I'll use the factory wiring plus pigtails with the Phillips 9003 bulbs in the Cibies. Aim them properly (thanks for the link) and I'll be good to go.
Eventually the Phillips 9003 bulbs will need replacing. At that point, would you recommend a different bulb? And should I then consider adding in the SMS wiring harness?
Then I'll use the factory wiring plus pigtails with the Phillips 9003 bulbs in the Cibies. Aim them properly (thanks for the link) and I'll be good to go.
Eventually the Phillips 9003 bulbs will need replacing. At that point, would you recommend a different bulb? And should I then consider adding in the SMS wiring harness?
Alaric Darconville
Flashlight Enthusiast
Philips X-Treme Power has been superseded by the Philips X-Treme Vision, and is available in the 9003. The NightHawk Platinum (by GE) is also a fine choice.
I thought you were going to use the harness with the Cibié lights. If you've tested for voltage loss in accordance with this and find you need 'em, install 'em!
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