# Car Headlights **URL:** \ **Category:** Factual Questions\ **Created:** [February 21, 2010, 1:25am UTC](https://boards.straightdope.com/t/car-headlights/529828 "2010-02-21T01:25:23Z")\ **Posts on this page:** 11\ **Page:** 2
**Author:** ![figure9](https://avatars.discourse-cdn.com/v4/letter/f/f0a364/32.png) [@figure9](https://boards.straightdope.com/u/figure9)\ **Post date:** [February 23, 2010, 11:18pm UTC](https://boards.straightdope.com/t/car-headlights/529828/21 "2010-02-23T23:18:05Z")
Since the bulbs failed 10-14 days apart I think it is unlikely to be a relay/wiring problem. I am still thinking it is dirty/loose connectors at the bulb or bad bulbs. ---
**Author:** ![unclelem](https://avatars.discourse-cdn.com/v4/letter/u/ac91a4/32.png) [@unclelem](https://boards.straightdope.com/u/unclelem)\ **Post date:** [February 23, 2010, 11:57pm UTC](https://boards.straightdope.com/t/car-headlights/529828/22 "2010-02-23T23:57:25Z")
there have been several recall notices on problems like this with various honda models. I would check with a dealership to see if the problem applies to your vehicle. If they say “no”, then I would check with a different dealership to make sure the first one wasn’t lying to me. The recall issue appears to be a problem in the switch that turns on the (low beam) lights. One of the wires is too thin, overheats and then no longer works. The symptom is that the high beams work and the lo beams do not. I suppose that potentially this could become an intermittent problem. There have been reports on the web that some vehicles seem to have exactly this issue even though Honda claims they are not affected by any particular recall notice. I would try to get them to fix it for free under a recall notice first. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [February 24, 2010, 12:06am UTC](https://boards.straightdope.com/t/car-headlights/529828/23 "2010-02-24T00:06:18Z")
> [@Gbro](#): > > Rick, on that surface charge; > I see that often when I test a charging system at the store. How do you eliminate this before testing to get a true reading? > Is it more prevalent with a dirty old battery vs a new one, or is the surface discharge that I am thinking about unrelated? > > Thanks for the information.🙂 Turn on the headlights for 30 seconds or so, or just leave the key in the on position for say 30 seconds or so. This will remove the surface charge so you can get an accurate reading. ---
**Author:** ![Gbro](https://avatars.discourse-cdn.com/v4/letter/g/c6cbf5/32.png) [@Gbro](https://boards.straightdope.com/u/Gbro)\ **Post date:** [February 24, 2010, 2:54am UTC](https://boards.straightdope.com/t/car-headlights/529828/24 "2010-02-24T02:54:27Z")
> [@Rick](#): > > Turn on the headlights for 30 seconds or so, or just leave the key in the on position for say 30 seconds or so. This will remove the surface charge so you can get an accurate reading. I had a couple more questions, But googling helped me after your post gave me answers to puzzling conditions i have seen and did not understand:smack: [This link](http://www.prestolite.com/pgs_training/training_2.php), although a big rig link helped me also. Thanks again ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [February 24, 2010, 5:22am UTC](https://boards.straightdope.com/t/car-headlights/529828/25 "2010-02-24T05:22:32Z")
**Gbro** no problem, if I can answer any other questions feel free to ask. > [@Fridgemagnet](#): > > **Rick** , I do apologise profusely if the numbers I pulled out of my butt don’t meet your cromulence expectations, and you’ll forgive me my rounding error on the 12 V quote. The lack of decimal places here is a clue to the given accuracy. But you will find that in-car electronic systems are rated at 13.4 V, which is the average system voltage with the engine running. It can’t be too much higher than this or bulbs will start blowing; too low and the battery won’t charge fully, or will take too long to charge and won’t reach full capacity. BTW, did you mean an internal battery resistance of 0.2 _ohms_ per cell? In which case, the actual cell voltage will depend upon the charging current. As well as the battery temperature, the integrity of the plates, the pH of the acid, and so on, there are many variables. For the record, I earn a living as a freelance electronic designer producing circuits for things like battery chargers and alternator regulators, and I take care to retain my hard-earned BS-free reputation, as the job market says I’m only as good as my last design. > > All the details of sealed lead-acid battery charging can be found at the excellent [batteryuniversity.com](http://www.batteryuniversity.com/partone-13.htm). First off we are on a message board that is dedicated to fighting ignorance, not prolonging it or perpetuating it. That is the cool thing about stuff technical, either the answer is right, or it is wrong. Your answer was wrong. Saying that a 12 volt battery produces 12V with no qualifier that a fully charged 12 battery is 12.6+ volts and then saying that the lack of a decimal place is due to given accuracy is about like a mathematician saying that Pi is equal to 3 because he could not figure out how to set the calculator to display digits to the right of the decimal place. A convenient excuse, but not a right answer. Also funny you could put one significant digit to the right of the decimal when giving the wrong alternator charging voltage, but that significant digit was beyond you when giving battery voltage. If you do in fact design battery chargers and alternator regulators for automotive use, you might want to look up the design specs for a GM CS-130 which in very cold weather can charge in the vicinity of 16 volts. About resistance. I said voltage and I meant voltage. The internal resistance in the battery requires a charging voltage that is about .2 volts above the nominal battery voltage. That assumes a proper charging current. If you try and cram too many amps into the battery, since the internal resistance does not change, to accommodate the additional amps, the voltage has to go up. Ohms law, it is not only a good idea but the law, and it is not subject to repeal. Anyone that designs battery chargers should know this cold. BTW did you even bother to read the cite you provided? > [@](#): > > Correct settings of the voltage limits are critical and range from 2.30V to 2.45V. Let’s do the math. 6 cells X 2.3 volts equals 13.8 volts. 2.45 volts/ cell would give a charging voltage of 14.7 Volts. Both comfortably above the 13.4 volts you are claiming. 13.8 minus 1.2 Volts for the internal resistance of the battery gives 12.6 Volts exactly what I said the voltage of a fully charged battery was. Reading a bit further they give a range of 2.26 to 2.37 V / cell for automotive and VRLA batteries. I suspect that VRLA batteries are the lower end of that range. And reading a bit further look at the chart they have for determining a battery’s state of charge by reading the open circuit voltage ```auto 12.65V 100% 12.45V 75% 12.24V 50% 12.06V 25% 11.89V or less Discharged ``` Look familiar? It should. It is essentially the chart I posted. But hey what do I know? I have only been doing this for over 40 years, am an ASE master automotive technician, was a technical training instructor for a car company for 15 years and edited the training manual on starting and charging systems. (Yes I am the guy that wrote the book) 😃 ---
**Author:** ![Fridgemagnet](https://avatars.discourse-cdn.com/v4/letter/f/22d042/32.png) [@Fridgemagnet](https://boards.straightdope.com/u/Fridgemagnet)\ **Post date:** [February 24, 2010, 9:47pm UTC](https://boards.straightdope.com/t/car-headlights/529828/26 "2010-02-24T21:47:16Z")
You are absolutely correct **Rick** , and I take my trousers down to your superior automotive skills. From now on I will specify equivalent series resistance in volts, not ohms, magnitude of current notwithstanding. In years to come I can only hope to be like your good self and be so secure in my position and respected by my peers that I would never consider attempting to raise my profile by belittling any contribution that I might disagree with. And if I did, then hey, manners are for the people that don’t matter. To be fair to Rick, I was disingenuous in my reply to his post - weaselwordsRme. And there’s a big difference between the charging methods employed by alternators and lead-acid battery chargers (I didn’t make the distinction, but read alternators). And forgive me my decimal places, and those who decimal place against me, for those figures I quoted are from dimly remembered measurements taken several years ago. And though in-car electrical equipment has a nominal line voltage of 13.4 V, there will always be an allowable range either side of this designed in. The voltage seen by such equipment will be a little lower than the battery voltage due to copper losses in the wiring and ohmic contacts in the switches, relays and connectors. Although incandescent bulbs are sensitive to overvoltage (the lifetime of a halogen bulb will be halved at a mere 5-10% overvoltage (disclaimer - butt figures)), some auto bulbs have overvoltage protection these days. Interestingly, halogen bulbs also suffer during undervoltage conditions as they are unable to undergo their crucial “halogen cycle”. As for what constitutes a normal battery charging voltage, opinions vary, even from the OEMs: [Car Batteries are Not 12 Volts](http://landiss.com/battery.htm). It seems they can’t agree on a right answer. **Jinx** , I am sorry for participating in a micturating match in your thread, I only hope you can glean some useful information out of the noise that enables you to fix your headlight issues. I’m out of useful information, so I bid the thread goodbye before it degenerates further, and wish you success. ---
**Author:** ![Mapache](https://avatars.discourse-cdn.com/v4/letter/m/58956e/32.png) [@Mapache](https://boards.straightdope.com/u/Mapache)\ **Post date:** [February 25, 2010, 2:00am UTC](https://boards.straightdope.com/t/car-headlights/529828/27 "2010-02-25T02:00:13Z")
If anybody finds out the definitive answer to Jinx’s problem, I hope they’ll post it here. I have a 2005 CRV and I’m on my fifth righthand low beam bulb. None of the other bulbs give any trouble, and the local Honda dealer hasn’t got a clue as to what’s going on. At least the cops in Oaxaca don’t ticket people for blown lights; if they did they wouldn’t have much time for anything else. ---
**Author:** ![SecTech](https://avatars.discourse-cdn.com/v4/letter/s/ea666f/32.png) [@SecTech](https://boards.straightdope.com/u/SecTech)\ **Post date:** [February 25, 2010, 8:27am UTC](https://boards.straightdope.com/t/car-headlights/529828/28 "2010-02-25T08:27:32Z")
> [@Fridgemagnet](#): > > I’ve never heard of a lighting design that cuts a circuit to a blown bulb; doesn’t mean to say they don’t exist, but I can’t think of a particularly good reason why this should be done. Not exactly a lighting system, but I have X-ray machines that use the filaments of the “X-ray ON” indicator lamps as part of the safety/interlock loop. At power on, a relay closes, one set of contacts is used in that loop in a “holding” circuit to keep the relay energized. One lamp going out disables the machine the same as an Emergency Stop button being pushed, or an interlocked door being opened. Could this not be the same in the Honda, using the lamp filament resistance/continuity to “hold” a relay until power to the lamp is provided. No voltage would be measured at the lamp until the light switch is activated. At which time the first relay would drop out, and the “low beam” relay kick in. I believe this might go to the “weak” wire on the light stalk mentioned. I had a Pontiac Grand Am, that I replaced the accessories control on the steering column, twice, for a similar problem. Lights went out while on a night drive on twisty roads in some remote area of SC. Scary. ---
**Author:** ![Gbro](https://avatars.discourse-cdn.com/v4/letter/g/c6cbf5/32.png) [@Gbro](https://boards.straightdope.com/u/Gbro)\ **Post date:** [February 25, 2010, 3:08pm UTC](https://boards.straightdope.com/t/car-headlights/529828/29 "2010-02-25T15:08:45Z")
> [@Jinx](#): > > A friend may help me diagnose today. I’ll let you know what we find. BTW, ironically the problem started with my left bulb as well…but the dim setting, not highbeams. (Would a halogen bulb create a yellow smoke stain, or only the older-style bulbs?) What is puzzling to me with this Toyota headlamp arrangement is your vehicle is a 4 headlamp system (high beam and low beam being separate lamps, however they are identical headlamp bulbs [BP1255H1](http://www.rockauto.com/catalog/moreinfo.php?pk=319193) Are the currents different from high to low, or the len’s/diffusers just so much different??? Unrelated, but interesting story. One of the local repair shops called for a BP9003 bulb witch is a duel filament bulb that he was replacing in a Toyota and came back 30 min later for a second one. Along with instructions on bulb blister pac’s to “Not touch bulb with bare hands” is instructions to replace both bulb. Well he was only replacing the burned bulb and the other failed right there in the shop. He admits to never replacing a working bulb and that this was just a coincidence.:dubious: ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [February 25, 2010, 3:55pm UTC](https://boards.straightdope.com/t/car-headlights/529828/30 "2010-02-25T15:55:26Z")
> [@Jinx](#): > > Consulting a friend of his works on Hondas who says the circuit is “cut” (i.e., no voltage) once the bulb dies. Must be some kind of “smart circuit”, but for what purpose? I don’t know what this friend was thinking of, but he’s wrong. There is no interruption to the power or ground of the circuit when a bulb goes out. There would be no purpose to such a set-up, just needless complexity. > [@Jinx](#): > > My friend says there was no power to the low beams… I find this highly suspect. Both high and low beams are powered by the same relays and the same fuses (one relay and fuse for the left, one of each for the right). Switching for high beams is done through ground. To have power to the high beams but not to the low beams would mean that both the left low beam power wire and the right low beam power wire have problems, which is very unlikely. This type of bulb is very sensitive to surface contamination on its glass. If those bulbs were touched by fingers during replacement, that alone could result in very short bulb life. If this happened, replace them again and make absolutely certain that the bulb glass is NOT TOUCHED BY BARE FINGERS. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [February 25, 2010, 5:58pm UTC](https://boards.straightdope.com/t/car-headlights/529828/31 "2010-02-25T17:58:04Z")
> [@Gbro](#): > > What is puzzling to me with this Toyota headlamp arrangement is your vehicle is a 4 headlamp system (high beam and low beam being separate lamps, however they are identical headlamp bulbs [BP1255H1](http://www.rockauto.com/catalog/moreinfo.php?pk=319193) > Are the currents different from high to low, or the len’s/diffusers just so much different??? It is not unknown for the high and low beam bulbs to be the same bulb with different lens and reflectors. On the gas discharge lamps on the cars I work on, the bulb only has one brightness. High and low is accomplished by moving the reflector and or the lens to change the beam pattern and focus. Getting back to the OP I called a buddy of mine who is a master tech and a service manager at a Honda dealership. He asked around his shop and no one there had seen this issue. he wondered if there was condensation inside the housing. Until something definitive is reported back I am leaning toward either condensation or fingerprints on the bulb as the cause. [Previous page](https://boards.straightdope.com/t/car-headlights/529828.md?page=1)