By on June 14, 2019


Randy writes:

A few weeks ago I installed a pair of 9003 Philips Vision Plus 30 bulbs in an attempt to improve my wife’s Tucson headlight output. The light down the road is pathetic yet the headlight lenses are clear and the reflectors are still mirror like, at least to the extent I can see from the bulb mounting opening. And the light patterns are well defined, both low & high beam, which also suggests the reflectors are okay. But no joy whatsoever from the new bulbs.

I then did some voltage tracing down the headlight schematic. There is ~14.4 V coming from the alternator & battery into the SJB (smart junction box) that the Tucson uses to switch power to the bulbs. But only 12.5 V on the pins out to the bulbs. And then another couple of 1/10th V loss down the 0.5 mm2 (~20 AWG) wire to the headlamp connector netting 12.2 or 12.3 V at the bulb. The lead electrical tech at a local Hyundai service department says this is 2V headlight wiring voltage drop normal, even as much as 2.6V.

BUT, by my calculations, this means that although DOT specs for 9003 bulbs indicate 910 lumens (+/- 10%) at 12.8V, my wife’s car will be generating a little less than 800 lumens at the voltage actually supplied to the bulb. No wonder night driving is such a frightening experience.

I’ve toyed with the idea of trying some off road 90/100 9003 bulbs under the notion that at this lower voltage the output would be only 30 percent or so above the DOT standard and not likely to be blinding to oncoming traffic. And one hopes not so hot as to melt anything in the headlight assy. But I’d still wind up putting ~7 amps down a pretty thin wire which at 14 A/mm2 is double the recommended maximum current density I’ve seen for automotive wiring. I don’t wish to trade better light for burnt wiring or perhaps a fried SJB @ several hundred $.

My best idea at the moment is to wire the headlights via some fused relays using the car’s high/low circuits to switch the relays. I’d happily trade shorter bulb life for safe night vision.

Can anyone suggest an alternative solution? And yes, I’m aware of HID and LED “conversions” but am not willing to go that route, trading more lumens for rogue beam patterns.

BTW, is it common nowadays for headlight bulb voltage to be so low? Or is this unique to Hyundai? I realize that this improves bulb life … but at such a cost to safe night vision.

Sajeev writes:

I was about to recommend installing headlight relays to ensure maximum voltage to your headlight bulbs.  Then I remembered my experience: blowing out headlight bulbs (when flashing high beams) because said headlight relays were juiced directly from the alternator’s output wire. Apparently the correct source (this is on a Fox-body Mercury Cougar) was the starter solenoid since everything else starts there.

The point of this ramble? I have no earthly idea how to answer your question, but I know a guy…

Daniel Stern answers:

You’ve made some good observations, and you’re sniffing in a productive direction asking about bulbs and wiring and voltage.

First, let’s sharpen the picture of the voltage drop in your headlamp circuit. Voltage drop — that is, lower voltage at the demand end of the wires (the bulbs) than at the supply end (battery or alternator) — is caused by resistance in a circuit’s wires, switches, and connections. More resistance in the circuit means more voltage drop, and more current through a given circuit will mean more voltage drop than you’ll get with less current flowing through that same circuit. This means unplugging the headlights and probing the sockets won’t answer the question you’re asking, because that’s measuring the circuit with virtually no load on it: minimal current flow, so minimal resistance, so minimal voltage drop.

To get an accurate reading of the voltage drop, you have to measure the circuit with its normal current flow. That means all the bulbs have to be hooked up and working, and you’ll have to find a way to probe the socket without unplugging it. Some headlight sockets provide easy rear access to the metal terminals inside; if not, you may have to use a bit of cleverness: carefully insert a straight pin or unbent paperclip alongside each wire and into the socket until it makes contact, then touch your voltmeter probes to the exposed parts of the paperclips or pins. Or another technique is to remove the seal boot and probe the bulb terminals ahead of the connected socket. Avoid puncturing wire insulation unless there’s no other option and you’re prepared to effectively patch the hole immediately afterward.

On the HB2 bulbs in your car (other designations: 9003, H4), the terminal arrangement is as follows:

Left vertical terminal: Common
Top horizontal terminal: Low beam filament
Right vertical terminal: High beam filament

If your car uses a switched-feed headlamp circuit, the common terminal is the ground for both filaments, and the individual filament terminals are fed depending on the position of the headlamp on/off and high/low beam switches. If your car has a switched-ground circuit, the common terminal is the feed for both filaments, and the individual filament terminals are grounded depending on the position of the headlamp on/off and high/low beam switches.

You can put your voltmeter probes across the positive and negative wires and directly read the voltage at the bulb. To figure out where in the circuit the voltage drop is happening, put one probe at one end of the circuit (or the portion of the circuit you’re examining) and the other probe at the other end. For example: put the voltmeter’s positive lead on the battery positive terminal, and the voltmeter’s negative probe on the feed (+) wire or terminal of whichever headlamp beam (low or high) you’re testing at the moment. Use the bulb furthest away from the battery. With the lamps on, your voltmeter will show the voltage drop in the feed portion of the circuit, upstream of the bulb. Then connect the positive voltmeter probe on the ground terminal of the bulb, and the negative voltmeter probe on the (-) terminal of the battery. With the lamps on, your voltmeter will display the voltage drop in the ground portion of the circuit, downstream of the bulb. Adding the two voltage drop figures will give you the total circuit drop.

You raised the idea of using overwattage bulbs (100/90w), which you figure will still be brighter than stock despite voltage drop, but that’s actually not correct. A high-wattage bulb draws a lot more current than a standard-power bulb — about 65 percent more, in the case of a 100/90w bulb in place of a 60/55w bulb. That’s not just more current, it’s an overload, a whole lot more current than headlamp circuits are built to tolerate. Remember, more current makes more voltage drop and more resistance makes more voltage drop, so right off the bat you’re going to be much more significantly underfeeding the overwattage bulbs. The overload is going to heat up every part of the circuit and gradually cook stuff to death. Before that happens, though, your headlight performance is getting worse, not better: resistance causes heat (which is why light bulb filaments glow), and heat increases resistance, so depending on your luck you’ll have a vicious cycle of slow-roasted or quick-fried headlamp circuitry; neither is a tasty dish.

There are other good reasons to avoid overwattage bulbs, too; we’ll get to those in a minute. For now, let’s quantify the light loss we can expect as a result of voltage drop. Light output from a filament drops exponentially to the power 3.4 with voltage drop, so the formula to find the change in light output with a change in voltage input is: lumens @ spec volts x [(operating volts ÷ spec volts)^3.4] = lumens @ operating volts

910 lumens on low beam is the nominal spec for an HB2 bulb at 12.8v. There’s a tolerance allowed of plus-or-minus 10%, so an HB2 bulb producing anywhere from 819 to 1001 lumens on low beam is equally legal, but for these calculations let’s assume the bulb is right smack on spec and plug some numbers into our formula.

If the bulbs are getting 12.2 volts:

910 x [(12.2 ÷ 12.8)^ 3.4] = lumens we’re getting

910 x [(0.953125)^3.4] = lumens we’re getting

910 x 0.8494 = lumens we’re getting

773 = lumens we’re getting. So slightly less than a 5 percent voltage drop took a 15 percent bite out of our intensity.

If the bulbs are getting 11.8 volts:

910 x [(11.8 ÷ 12.8)^3.4] = 690 lumens (a little under 8 percent volt drop, 24 percent light loss)

It works the other direction, too; suppose we feed the bulbs 13.5v:

910 x [(13.5 ÷ 12.8)^3.4] = 1091 lumens (a little over 5 percent above spec voltage, a little under 20 percent more light than spec).

Or suppose we connect the bulbs via fat wires directly to full-boogie 14.4v off the alternator:

910 x [(14.4 ÷ 12.8)^3.4] = 1358 lumens (12.5 percent above spec voltage, 49 percent more light than spec).

So yes: feeding the bulbs a complete breakfast makes them put out more light, and starving them makes them feeble. But we might not want a zero-loss power path between the alternator and the bulbs. Bulb lifespan is also exponential with input voltage, but the exponent is much larger at -13 (negative 13), so the formula for bulb life looks like this:

hours @ spec volts x [(operating volts ÷ spec volts)^-13] = hours @operating volts

Let’s take a long-life HB2 bulb with a 1000-hour-at-12.8v low beam filament and run those same voltage calculations:

12.2v: 1867 hours (87 percent longer than spec)
11.8v: 2879 hours (almost 3x spec)
13.5v: 500 hours (half of spec)
14.4v: 216 hours (less than a quarter of spec)

This tells us why an automaker would prefer a little less rather than a little more voltage reaches the bulbs; it cuts down dramatically on bulb replacement costs under the vehicle warranty. Add the cost savings from using lighter-duty wire and switches, and multiply by the number of cars built, and, well, in the auto industry a fraction of a penny shaved from the automaker’s cost of a car earns someone a fat bonus and a promotion.

Warranty cost reduction is also a major reason why automakers tend to specify long-life bulbs as original equipment. But the filament changes required to make a long-life bulb tend to reduce luminance and beam focus, which means shorter seeing distance and a browner light color. The image shown here is from the R&D journal of Hella, one of the world’s foremost vehicle lighting manufacturers. It’s a comparison of the low beam seeing distance from a headlamp using a long-life bulb (3000 hours) versus that same headlamp using a bulb with higher luminance and better beam focus, but shorter lifespan (500 hours). This should go a fair ways toward answering why picking the longest-life bulb you can find and feeding it as high a voltage as you can would be a no-gain, zero-sum deal.

Now come those other reasons I mentioned for avoiding overwattage bulbs. For one, their lifespan is very short even at carefully-controlled voltage. But let’s say you really don’t care about bulb life; you’re happy to carry around a case of spare bulbs and change them every 10 days as long as you can see. But overwattage bulbs won’t help you see better — not really, it’ll only feel that way. High-watt filaments are bigger than lower-watt filaments, and a bigger filament has a strongly negative effect on beam focus, so effective seeing distance plummets. At the same time, the big increase in foreground light destroys your distance vision; the overlit foreground causes your pupils to constrict and drags your gaze downward, so you can clearly see all the things close to the car (at realistic road speeds you’re going to hit ’em no matter how brightly lit they are), but you can’t see the important stuff further down the road. Double-whammy, too; the bright foreground creates the false feeling that you have excellent lighting — we humans are very poor judges of our visual performance; our vision just doesn’t work the way it feels like it does, so it’s very easy to create situations where we think/feel we can see much better (or much worse) than we actually can, and while foreground light is the top correlate with subjective impressions of headlight performance, it’s really very far down the list of safety performance factors in a headlamp’s light distribution. Down-the-road distance light is much more important.

And on top of all that, you’re in a Tucson, which is an SUV with headlamps mounted higher than they are in a passenger car. Put overpower bulbs in, and you’re producing unsafe and illegal amounts of blinding glare for other road users (some of whom can write you tickets for it), unless you lower the lamp aim — and even a seemingly minor drop in aim angle severely limits your seeing distance (while increasing foreground light even more). Lose/lose.

But wait, there’s more! Since overwattage bulbs aren’t legal in any country developed enough to have traffic lights, there’s no reason for automakers to specify (or pay for) headlamps that can tolerate the much greater heat output of high-power bulbs. You might get away with it for awhile, but even if your headlamps don’t turn into flaming rivers of molten goo right before your very eyes, they’re suffering. The reflector is shiny by dint of a super-thin layer of vapor-deposited aluminum with a super-thin protective clear topcoat. The heat from a high-power bulb degrades the topcoat, then the aluminum oxidizes and the reflector’s shot to hell, even if it still looks nice. Optical degradation of the reflector is severely advanced well before you can see it with the naked eye; by the time it’s progressed far enough to be described as “pretty good, just a little imperfect” the lamp is a zombie, long past dead. In optics the important stuff happens on a scale we can’t see with our eyes: a headlamp reflector and the bumper of a vintage show car look equally shiny to us, but an as-new headlamp reflector is over 97 percent reflective, while even the most costly, beautiful show chrome is only about 67 percent reflective — not nearly adequate for optical purposes.

So let’s look at better bulb options. Bulb selection matters a lot to how well you can (or can’t) see at night. It pays to be picky, because there’s a mountain of junk on the bulb market, a lot of it is overpriced, and of course it’s all promoted as an “upgrade”. You were headed in the right direction when you picked up those +30 bulbs, but you’ll want to go further down that road. The +30 bulbs you got were state of the art about 20 years ago; since then we’ve progressed: +50, +80, +90, +100, +120, etc.

What do those plus-numbers mean, though? It’s not the amount of light coming from the bulb, because again, that’s pretty tightly controlled: plus or minus just ten percent on the HB2 low beam. In fact, the plus-numbers refer to intensity within the headlight beam. We already talked about the performance-degrading effects of optimizing a filament for long life; the opposite filament changes are made to create the “plus” bulbs, with the opposite effects: lifespan is reduced, but luminance and beam focus are improved so you get to see better and longer, and the light isn’t as brownish. The important thing to understand is that even if all the filaments put out exactly the same amount of light — the same lumens from a long life bulb, a standard bulb, +30, a +80, etc. — the headlamp performance and appearance with the long-life bulb would still be inferior compared to the same headlamp performance and appearance with a “plus” bulb.

That’s enough theory to understand the bulb test results posted here by a far-flung colleague of mine. Take a look at the giant differences in beam performance between a standard 60/55w bulb and a “+80” 60/55w bulb! Also note how the only advantage the 100/90w bulb gives is in amount of light on high beam. Seeing distance on low beam is inferior to that from the “plus” 60/55w bulb.

So okeh, to see as well as possible you’ll want to skip the overwattage bulbs and the weak standard and long-life bulbs; now let’s eliminate some more bad options in another fell swoop: any bulbs claiming to produce “extra white” light is best avoided (or super white, hyper white, platinum white, metal white, xenon white, etc). It doesn’t matter whose name is on the bulb — Sylvania Silver Star or ZxE, Philips BlueVision or CrystalVision, Wagner TruView, anything from PIAA or Hoen,, Nokya, Polarg, etc. — all the same bad deal. They have blue-tinted glass which changes the light color a little but blocks light that would reach the road if the glass weren’t tinted, so they give you less light than ordinary bulbs (not more). It’s purely for fashion; these bulbs (poorly) imitate the color, but not the performance of higher-technology HID and LED headlamps. The filament has to be driven very hard to get legal-minimum levels of light through the blue glass, so these kinds of bulbs have a very short lifespan, and there’s nothing about the tinted light that improves your ability to see — the opposite is true (less light = less seeing, no matter about the tint). A couple of years ago Sylvania got spanked pretty hard (30 million dollars’ worth!) for false and misleading “upgrade” claims on Silver Star bulbs, and theirs are among the least-bad ones, so the math kind of does itself: you’ll want to reject the whole category.

My current favorite 60/55w H4/HB2/9003 bulb is made by Tungsram (GE of Europe); it is a +120 item that is a few developmental iterations improved over the +80/+90 bulbs in the linked comparison tests. I bring them over from Europe in wholesale quantity, but they’re also available (usually at a price I have a hard time seeing as cost-effective) in American GE packaging as seen here — replete with the usual clue-deprived “reviews”. Another solid pick is the Philips Xtreme Vision +100, more reasonably priced as seen here. Occasionally there’ll be a screamin’ deal price drop on one or another of these premium bulbs; right this minute here’s a super price on the Philips Xtreme Vision +130, though it could be gone by the time you read this, and Canadian prices and deals are going to be different.

Narrowing in even further, what’s to pick among these +100, +120, +130 types of bulbs? Rather than just shooting for the highest plus-number, you’ll want to pick ones with the least amount of blue-tinted area on the bulb glass. The Philips and GE +130, the Sylvania Silver Star Ultra, and the various Osram Night Breakers have an uncolored ring surrounding the low beam filament, but the whole rest of the bulb, including the area the high beam filament shines through, is blue-tinted. That means you’re losing some performance on high beam for useless fashion points. The Philips +100 and the GE-Tungsram +120 have only a thin blue ring right below the tip of the bulb, which doesn’t affect performance at all. The marketers say it’s is there to make a fashion statement with your headlamps, etc, and yes, from various off-axis angles as you observe the headlamp, you do see some blue glint, but it’s really there to sneak the bulbs past their type-approval tests. The regs strictly limit bulb output to not more than 10 percent above the nominal spec, remember? That’s tested in a device called an integrating sphere, which measures the bulb’s total output in all directions. The blue ring filters a part of the bulb that has nothing to do with beam formation because it’s not in the light path between the filament and the reflector. So that blue ring gives fashion-fixated kids of all ages a blue flash they can point to from certain irrelevant angles without coloring the beam or filtering out any usable light. It gives the marketers something to babble about so the bulbs fly off the shelves. Meanwhile, the filament is pumping mad lumens through the uncolored glass where the reflector is looking — a clever trick that really works.

If you want to wring maximum possible light out of the headlamps, no matter how short the bulb life might be, that’ll take the optimal bulbs and a relay install done thoughtfully and properly (i.e., make sure you’re putting in components dependable enough to entrust your life to, because that’s what you’re doing); hints are here. But there’s one other reason why you might not want to install a headlamp relay harness: if your vehicle uses the headlamps as DRLs (daytime running lights), then in many cases you can’t put in a relay harness without making problems: most headlight-based DRL systems operate the low and/or high beams at reduced voltage compared to what they get when you turn on the headlamps to drive at night. High beam DRLs operate at about 50 percent of normal voltage; low beam DRLs at between 75 and 85 percent. Full-intensity low beam DRLs are only allowed if all the lights normally lit with the headlamps — parking lights, tails, side markers, license plate, etc — either come on full time with the DRLs, or come on automatically when it gets below a certain darkness outside. Full-intensity high beam DRLs aren’t allowed at all. But the lights will run at full intensity if you install a headlight relay harness on such a vehicle, meaning the DRLs will be operating in an unsafe and illegal manner until the relays burn out, which they will. If you’re bound and determined, you can disable the headlight-based DRLs (easier on some vehicles than others) and move the DRL function to the front turn signals with a module like this, or install a reputable-brand (Hella, Philips, Osram/Sylvania) set of LED DRLs.

Now we’ve finally sorted out what to do about bulbs and wiring: lamp aim is by far the main thing that determines how well you can (or can’t) see at night with any given set of lamps, so this is crucial: you will need to see to it that the lamps are aimed carefully and correctly with an optical aiming machine as described here. It can be difficult to find a shop that has (and uses) an optical aiming machine; keep calling around until you get the right answer — and “we shine ’em on a wall/on a screen” is the wrong answer. To get an idea of what a proper lamp aim job looks like, see the VW document presented here.

One final point: you’re absolutely right and very smart to steer clear of so-called “HID kits” and “LED bulbs”, every last one of which is illegal and unsafe. Halogen lamps can only work effectively, safely, and legally with halogen bulbs.

[Image: Shutterstock user Fahroni]

Daniel Stern has been a freelance vehicle lighting consultant for decades. He’s on several of the world’s technical standards development boards for vehicle lighting, and is Chief Editor of DrivingVisionNews, the global vehicle  lighting and driver assistance industry’s journal of record.

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.
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39 Comments on “Piston Slap: Droppin’ Knowledge on Headlight Wiring Voltage Drop...”

  • avatar
    golden2husky sells relay kits for this exact purpose.

    Please don’t “overlamp” your vehicle and blind others…some of these bulbs produce horrid bluish light…they create horrid glare.

    • 0 avatar

      Many of the blue lights you see aren’t due to voltage or wattage issues, instead they just have a different Kelvin temperature. Higher K = bluer. You see this in various aftermarket bulbs, this article explains it well:
      As newer, better lights hit the market this blue look gain popularity because they were featured on many high-end German models. Thus people started associating blue to higher quality (and cost). This is especially true since older bulb technology produced a yellowish tint. Thus the race to make high Kelvin blue lights was on and now we all suffer every night.

      • 0 avatar

        That’s not how it works. Early HID lights were overall whiter than halogen (a higher color temperature), but they happened to have a strong narrow spike in the blue frequency range. It’s that stupid blue spike that got associated with fancy headlights. It’s a bug, not a feature.

        Modern HIDs do not have the blue spike, nor do LED headlights.

        • 0 avatar
          Daniel J. Stern

          Actually, krhodes1, JMII got it right; his comment is bang-on accurate (though his link is full of poo, not surprising given that its intent is to sell stuff, not to educate).

          The output spectrum of what you are calling “modern HID headlamps” contains _more_ blue light (a higher/bigger blue spike) than the earliest ones. And legitimate LED headlamps have even greater blue content (even higher/bigger blue spike in the output spectrum) than any legitimate HIDs. And HID headlamps are “whiter” than halogens only in the imaginative world of marketeering babble; light with a higher CCT from an HID or LED headlamp is not “whiter” in any real sense than light with a lower color temperature from a halogen headlamp.

  • avatar

    Great stuff, Daniel!

  • avatar

    Now, if I could find some better lights for the Cobra.

  • avatar

    Very thorough response. Though, instead of the relay route or potentially messing with SJB output circuits which are often monitored, LEDs are my preferred go-to. I know you said you didn’t want LEDs, but they’ve really gotten pretty good and the better kits have clockable bulbs to correct any rogue beam patterns.

    • 0 avatar

      About the only LEDs I’d consider (in my Tacoma) are the Philips x-TremeUltinon bulbs. They’re pricey (around $200USD a set)

      • 0 avatar
        Daniel J. Stern

        Pricey, yes…and even so, they still don’t work acceptably. Just the other day I got in a pair of Philips’ newest Gen-2 Xtreme Ultinon H4 LEDs and put ’em in some headlamps on the test bench to see how they’d evolved from the Gen-1. Result: fail, fail, fail, fail, fail; the beam pattern damage is severe and really detrimental to the headlamp’s safety performance. Wrong amounts of light in the wrong places—too much in some places, not enough in others, which boils down to inadequate seeing and excessive glare, no matter how cool anyone might think they look.

        It is flatly wrong to state that so-called LED bulbs for halogen headlamps have not “gotten pretty good”. No, they have not. They are not a legitimate, safe, effective, or legal* product, no matter whose name is on them or what the vendor claims. A halogen lamp—any halogen lamp—equipped with one of these will not produce an appropriate, proper, safe, or legal distribution of light.

        There is a task force within the Society of Automotive Engineers Lighting Systems Group working to devise a technical specification for LED retrofit bulbs for use in halogen lamps. The technical challenges to making such a retrofit bulb that actually works acceptably are eventually surmountable, but they’re pretty tall, and so really effective LED retrofit bulbs are still several years away. When they become available, the situation will actually be more complicated than it is today, because then consumers will have to discern between legitimate and fraudulent LED bulbs: “some of them are OK and others aren’t”.

        But for now, the situation is comparatively simple: Halogen lamps need to use halogen bulbs or they don’t (can’t, won’t) work effectively, safely, or legally. This is not like trying out different bulbs in the kitchen or living room or garage, where all it has to do is light up in a way you find adequate and pleasing. Headlamps aren’t just flood or spot lights; they are precision optical instruments (yes, even a cheap and minimal headlamp counts as a precision optical instrument) that have a complex, difficult job to do in terms of simultaneously putting light where it’s needed, keeping it away from where it’s harmful, and controlling the amounts of light at numerous locations within the beam to appropriate levels (too much light in certain areas is just as dangerous as not enough). Headlamps cannot just spray out a random blob of light, and that’s what they do with anything other than the correct kind of light source.

        *”Legal” is a bit of a slippery target in North America, because the regs are laxly enforced and do not adequately address the aftermarket. There are stringent standards that apply to headlights and bulbs installed by a vehicle maker as original equipment, and to any replacement parts installed for any kind of pay (by a dealer, independent repair shop, “upgrade” shop, guy working out of his garage, etc) but those regs don’t apply to vehicle owners, and Customs, although they could, don’t do much to stop the flow of unsafe aftermarket lighting equipment imports. However, this does not make an anything-goes situation; states (and Canadian provinces) can still enact vehicle equipment requirements requiring vehicles used on public roadways to have lighting equipment that complies with the applicable national standards — thus extending the stringent regs to cover not only automakers and repair businesses but also end users/consumers.

        But even if one happens to live in a place where the vehicle equipment code is silent on the matter, or is laxly enforced, there can be severe liability consequences to using unsafe lights. After a crash, if a vehicle is found to have lights that don’t meet the standards they’re supposed to meet, and that is even potentially a contributing factor in the crash, the owner of the vehicle stands to get absolutely *hosed* in court, and could face ruinous liability costs. So grinning and saying “Well, it’s not illegal where I live” or “Well, the cops don’t care” is foolhardy.

        Nevertheless, even major brands (Philips, Sylvania) have taken advantage of the outdated limitations in the national standards to market what they claim are LED retrofit bulbs for halogen headlamps. It’s unfortunate that they’re allowed to profiteer this way, but that’s the situation. Forget buyer beware, try buyer be *wise* and just…don’t.

        • 0 avatar

          Example. My 2017 Chrysler 300S had the base lighting (non HID, non adjusting). These were dangerously dim at night, and the IIHS agrees. I took the beam pattern on the wall at 25ft and again at 50ft and 100ft with high beam shutters open.

          I installed a pair of ProLux LEDs and clocked them and adjusted the headlamp assemblies until the pattern was approximately matched, low and high beam. The result, FAR better visibility and NO ONE flashes their high beams back at night, something that factory equipped HID 300s can’t claim.

          You can go on about technicalities and legalities, but if installed correctly, the LED conversion can net a big improvement. In my car, the FET protection wouldn’t care much for a janky relay setup, so this was the way to go.

          • 0 avatar

            Your methods make so much sense. I wonder why GM–the poster child of cost-cutting–hasn’t adapted your methods for testing headlamps. Take a known reference headlamp that performs decently and then design the new Yukon’s headlamps to “approximately match” the output of the good reference lamp!

            And then for final validation, just take a spin around Detroit and see if anyone flashes you!

            With this knowledge, you could easily put me and D.S. out of jobs! Any college intern could do this!

            Goniophotometer time isn’t cheap, as D.S. knows. Neither is funding the trial-and-error that is headlamp design. It’s not as simple as slapping a projector from Hella together with a curved lens as dictated by the styling department.

            I know the point will be lost on you, but the fact of the matter remains: headlamp development for each car costs millions, and it’s not because of the strippers and blow.


            Your 300S has some unfortunate headlamps, but two rights don’t make a wrong. The area of the beam pattern on a wall that causes glare is just a small rectangular area even at 25 feet away. I suspect that you haven’t got the slightest clue of where to find this “glare box.” Plus, I suspect that your eyes aren’t quite sophisticated enough to determine if the glare thresholds of 700/1000 candela have been exceeded.

          • 0 avatar

            I’m not claiming to be an expert, I’m not in this area. However, without the big budget to hire a guy like you, I worked with what I had and the headlamps work far better than before with no discernible negative effects. The alternative were headlamps that worked poorly. They were designed by qualified people that presumed whatever spec was issued to them to be adequate. They weren’t.

            Overloading the halogen bulbs seems like an ever poorer choice as I’d end up spending more time with burned out bulbs. If you guys could maybe just spend a little more time on these things, then we wouldn’t have to modify them and we could all be satisfied!

          • 0 avatar

            The base halogens on the 300 are actually acceptable. You cite the IIHS as saying the 300’s lamps were “dangerously dim,” but in fact, this is what they say:

            “On the straightaway, visibility was good on the right side of the road and fair on the left side. On curves, visibility was inadequate in all 4 tests.”

            The lamps are hardly dangerously dim on straight stretches of road. Curves do leave something to be desired, however, but the lights objectively provide good seeing distance down the right side of the road.

            I’m not sure what you mean by “overloading” the halogen lamps but that isn’t the advice provided. The advice provided in the article is to simply aim the lamps and provide more slightly more voltage to the lamps if the factory wiring is inadequate or degraded.

            It just goes to show that human perception is rarely accurate. You think your lamps are “dangerously dim,” but the IIHS reports that the lamps provide a fair bit of seeing distance straight down the road. People fail to realize that human perception is actually really bad. A good example of how human perception fails is the sheer number of people who feel that it’s safe to drive after a fifth of vodka. You might feel that you are in control, and that you’ll get home safely, but the reality is that a good number of ’em end up in the tank, the morgue, or in court.

            Lamps are unfortunately developed as much by the styling department as they are by the actual engineers. That’s why not every vehicle on the road today has a set of exemplary lamps. It’s basically impossible in many cases to design a set of lamps that will satisfy the accountants and the stylists while providing good performance. The current trend is toward smaller and more aerodynamic lamps. The Lexus IS250/350 used to have curve-adaptive lamps, but in 2011, the addition of the LED DRL strip caused the curve-adaptive feature to be removed. Just one in a thousand examples of style trumping engineering. The LED DRL strip cost more money, so something had to go to balance out the cost.

            A good example is the sheer number of vehicles in the US with red turn signals. Red turn signals have been proven time after time in the last 40-50 years of traffic safety research to increase the risk of crashes. Every country except the U.S. has mandated amber turn signals. Yet the U.S. trudges on stubbornly, even after the NHTSA itself released a report stating that red turn signals are dangerous. Vehicle stylists simply do not care. Red taillights look more attractive than red and amber taillamps. The back of your 300C is a solid red. Looks great. The back of its stablemate, the Charger, is also a solid red. There’s no amber to be found on either one because well, it looks good without the amber, according to the various focus group panels conducted by automakers. People simply don’t like the look of amber taillamps, safety be damned. Blame the engineers all you like, but the reality is that the engineering department is often trumped by the stylists and accountants.

            Moan that you can’t afford the expensive time of actual engineers, but in this article, you have 2 engineers, and you’re just ignoring all the free advice presented to you. Sounds like the issue is on your end, not on anyone else’s end, but that’s probably a hard pill for you to swallow.

  • avatar

    Wow, excellent write-up by Daniel. He helped me out 20+ years ago, when I was adding repeater lamps (I used Saab parts) to the front fenders on my ’95 F-150.

    My wife’s ’08 Sienna has headlights with just an okay cutoff, and a pretty poor overall beam pattern and reach. Cleaning them up helped some, and I run a set of the Philips X-tremeVision +100 bulbs (low-beam 9006; I run stock high-beam bulbs), which help even more.

  • avatar

    Daniel Stern clearly knows his stuff. And here I thought he hadn’t done much since Home Alone!

  • avatar
    schmitt trigger

    This post should be called “Everything you wanted to know about automotive headlamps but were afraid to ask”. Thumbs up!!

    The only minor thing that I could add, is as the automobile ages, their electrical circuits further degrade. Corrosion increases the contact resistance.

    An even worse voltage loss will eventually occur.

  • avatar

    I totally agree with Mr. Stern’s comments. Certainly about the blue tint being a “fashion statement” and detrimental to good lighting performance. I have given up trying to discuss lighting with most drivers. As Mr. Stern noted, most judge headlights by the near ground brightness which is backwards from what is needed to see hazards.
    Most seem to think that brighter/more light(s) will help them see better. Usually this will just waste money and or get you a ticket.
    BTW I have installed headlight relays on most of my vehicles, but they are ancient and do not have DRLs so a good result and little complexity.

  • avatar

    So your headlight is clear and reflector is fine, and your new bulb is not helping much. I’m not sure all the wiring change will be worth the extra 10% or so lumen, really. Can she use high beam when no other cars are around?

    What about adding extra light at the bumper level? Kids from the 90s like me used to see people adding “fog light” to the bumper to “make them see better”. If I’m going to reroute lighting I’m going to do that instead. Similar effort (at least in wiring), way more lumens.

    • 0 avatar

      Bumper-level lights are kneecapped by geometry. You’re mounting lights lower than the actual low-beams on your vehicle. This severely diminishes the ability of the extra lights to actually illuminate far out.

      Seeing every rock on the ground 20 feet from your bumper doesn’t actually help you avoid obstacles.

      Plus, extra lights on the front can obscure turn signals. Is this really what you want?

  • avatar
    cimarron typeR

    Many thanks to Mr Stern for sharing wealth of knowledge. My old ML350 didn’t have the lighting package (most didn’t) . I respect Mr Sterns and others’ opininon on retrofits and legality etc., but ultimately I was only satisfied with a 35 watt HID conversion kit from the Retrofit Source professionally installed by MB indy mech.We sold the car to a teacher at my daughter’s school and they are still functioning fine 7years out. Best 300.00 I’ve spent on a mod(100-150kit and labor).
    I drive odd hours for work and will never go back to base /halogen lighting again.

    • 0 avatar

      I personally have a problem with purchasing federally illegal lighting products.

      I’m not going to get into the photometrics. All I’m saying is that I have a hard time supporting a business who’s in the business of mislabeling their imported lighting products to avoid seizure by port officials.

  • avatar

    Don’t forget your Hella Supertones.

    At any rate, if you go the relay route, use one with a built in snubber diode, or install one in the circuit or you will introducing inductive spikes back into the electrical system, with unpredictable results.

    I put headlight relays on my Suzuki Bandit, which has notoriously evil lighting, and when I switched high/low, there was enough voltage across the coils to fire off both turn signals at once. A snubber diode will cure that. The relays, plus some Bosch projectors and heavier wiring (stock wiring was laughable) has given me impeccable night vision now. I tried to band aid it with a HID system and all I got was a crap beam. The silvering was off of the low beam reflector, so no amount of HID jiggery-pokery was going to fix it. The high beam reflector was another matter as it lit up the night like a damn klieg light.

  • avatar
    kjhkjlhkjhkljh kljhjkhjklhkjh


  • avatar

    I have been wanting to legally get either whiter light or more lumens in my current vehicle for a while, as the halogen warm white blends in with most of the overhead street lighting, making city driving, particularly when wet or right after sunset, particularly nerve-wracking.

    But Mr. Stern’s response was WAY too technical for me. I simply want to different halogen bulbs without changing the cut off or pattern. But the help at most auto shops just point me in the direction of the book by the bulbs to look up ‘what fits’, Audi will only do OEM bulbs, and the indie shop I prefer will install aftermarket bulbs, but only if I take the liability to make sure they are legal. He makes a bulb suggestion, but the bub he links to does not fit my vehicle according to Amazon. It will list ‘compatible’ bulbs, but mixes LEDs in (BAD!), and none list that ‘+xxx’ number he mentioned.

    Is there some retailer or database I can find to make sure I do this right?

    I’m lost.

    Also, what about fog lamps replaced by LED’s or at least a higher temperature color? Can I do that without breaking the law and angering other drivers?

    • 0 avatar
      Daniel J. Stern

      All the technical stuff boils down to this:

      • LEDs don’t safely or effectively go in place of halogen bulbs, whether it’s in headlamps or fog lamps (also, fog lamps should be turned off just about 100% of the time; see .)

      • You can waste a mountain of money buying bulbs that claim to produce what marketers want you to think is “whiter” light. It’s not whiter, and it’s not better in any real sense, it’s actually just bluer and dimmer.
      Any of the bulbs claiming to produce “extra white” light (or super white, hyper white, platinum white, metal white, xenon white, this or that color temperature or “kelvin rating”, etc) as its main promotional “benefit” is best avoided. It doesn’t matter whose name is on the bulb — Sylvania SilverStar/Ultra or ZxE, Philips BlueVision or CrystalVision, Wagner TruView, anything from PIAA or Hoen, Nokya, Polarg, etc. — all the same scam. They have a blue-tinted glass, which changes the light color a little, but blocks light that would reach the road if the glass weren’t tinted, so they give you less light than ordinary bulbs (not more). To get legal-minimum levels of light through the blue glass, the filament has to be driven very hard so these bulbs have a very short lifespan, and there’s nothing about the tinted light that improves your ability to see; the opposite is true (less light = less seeing, no matter about the tint). Sylvania got spanked ( ) to the tune of thirty million dollars(!) for false “upgrade” claims on their Silver Star bulbs — and theirs are among the least-bad of an overall bad product category, so the math kind of does itself.

      You don’t mention what year or model your Audi is, but the top picks readily available in the US are the Philips XtremeVision (like ), GE Night Hawk Xenon ( ) or Megalight Ultra ( ), and the Osram Night Breaker Unlimited ( ). Note how although these bulbs have blue bands on the glass, they aren’t located directly in the light path between the filament and the reflector, so they’re not cutting light that would otherwise reach the road. They will nudge your headlights’ appearance toward the “whiter” appearance you want, but keep in mind that halogen headlights will always look like halogen headlights.

      • 0 avatar

        2011 Audi Q5.

        Thanks for the links, I will check them out.

        I definitely want to see better at night, so if these help, then I am grateful. I want to make sure I’m legal while also not blinding other drivers. I’ve had that happen to me so many times. You think some one has their high beams on, so you flash yours on to remind them to switch to low beams, and then you get blinded when their actual high beams come one…because they either have their lights aimed too high or have some aftermarket stuff that is just wrong and damaging to other divers. I do NOT want to be that guy.

      • 0 avatar

        Also, I am going to peruse your website about another exterior light question.

        I will email you directly if I cannot find an answer.

        Thanks again.

      • 0 avatar

        I put a set of the sylvania blu blu bulbs in my saab. My wife asked me to take them out-I agreed, it was a failed experiment.

  • avatar

    Provided voltage is within range, 11 volts plus or whatever, it is Ground (-) that controls the brightness of lights, not the voltage. With minimum voltage and a good Ground, lights either turn ON, full output, or they don’t turn ON.

    In other words, a bad Ground will dim the lights. Besides checking for a solid (-) connection (wiring loom to body), check out the body “grounding strap” for corrosion, etc.

    • 0 avatar

      No, resistance anywhere in the circuit will cause the headlight to dim. Yes, if it’s on the ground it will cause it to dim as much as the power. Also it doesn’t matter how perfect the wiring and ground are. On a conventional bulb with a filament, halogen or not, the more voltage, the brighter until it burns out. The operating range is simply were they recommend it running on. It will still be brighter at 14V then 11V

  • avatar

    ? Only 20 gauge on a headlight feed ? .

    That’s terrible .

    NAPA’s Echlin line used to sell a very good and easy to install dual headlight relay that delivered direct battery current to both high and low beams, we’d install them on those 1970’s Japanese vehicles that also used improper 20 gauge headlight wiring and it made the stock seal beams work properly not to mention being able to power higher wattage Halogen bulbs without over working the original harness and switches, fuse boxes and so on .


  • avatar

    No, resistance anywhere in the circuit will cause the headlight to dim. Yes, if it’s on the ground it will cause it to dim as much as the power. Also it doesn’t matter how perfect the wiring and ground are. On a conventional bulb with a filament, halogen or not, the more voltage, the brighter until it burns out. The operating range is simply were they recommend it running on. It will still be brighter at 14V then 11V

  • avatar

    Thank you Daniel.
    Back in the day, we’d toss the DOT spec lights and insert H4 or H1 bulbs, depending. I had a Golf and a Jeep, each had the 7 inch H4 spec with normal 55/60 bulbs, then as an additional switched circuit, relayed off the high beam side, 100 watt H1 bulbs in separate driving lights. Provided you aimed the H4 correctly, you were in good shape.

    The current “blu bulbs” or the guy who runs around with an LED strip on, are just a public nuisance. Now, I get it…I’ve had bad lights on cars. The nonsense 9004 bulb comes to mind, but even that was good in the Volvo 240, which had a huge lamp to aim it….although most interations were horrid. Luckily, that bulb appears to have died out, finally.

    Lights can be wonderful. I have an LED setup on my C class that is bright, white, aims itself, and does not glare at all, while giving me the best light I’ve ever had . My MDX, with HID low and halogen highs, also does an excellent job. I’ve not felt the need to adjust or augment either car.

    One of the few places the IIHS and my issues align is in headlights and crash tests.

    I’ve been followed and glared by too many bogus LED lights. I’m not a violent person but I have a fantasy about carrying around a ball peen hammer…..

    • 0 avatar

      The Volvo 240 was able to wrangle acceptable performance out of the twin transverse filaments but because of how big the reflector was, beam focus was pretty much non-existent. The Volvo’s headlamps just created a big blob of light–its only saving grace was it managed to put more of that light on the road versus other 9004 systems, which barely put any light on the road.

      9004 was created by Ford with a focus on low system cost and long bulb life. The twin transverse filament orientation is rarely used in more modern bulbs. The twin transverse filaments pretty much limit each filament to using only half of the reflector.

    • 0 avatar

      I had H4s in my 914: amazing.

      I imported a Euro grill with factory monoblock aero H4 lamps for my gen-1 Jetta: amazing. However, my mechanic wired in a second set of wires & relay with a switch under the dash. Flick the switch off, and they were as sickly-weak and yellow-brown as the lights on any gen-1 water-cooled VW over 5 years of age. This was handy when the local cops were looking to bust people for aftermarket lights.

  • avatar

    Excellent read.
    I finally subscribed after lurking for a few years just to comment.
    Nice to understand why so many oncoming cars with headlight “upgrades” annoy me to no end.

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