Hi beam and lo beam power consumption?

[raj55]

BMW 3 series (e.g. BMW E90) uses H7 bulbs, one each for high and low beam. When they are switched on, are the power consumption different for high and low beam or are they same? That is to say, does BMW modify the power consumption (and there by modify out put) of these bulbs when using for high and low beam function?

There is a thread in a BMW forum asking the same question and it has created a sort of disagreement. My opinion is that the power consumption is the same but the light output is modified by the reflector. A gentleman who has worked for the BMW suggests that they are modified by the BMW.
Can some one please enlighten us?

Here is the link to that forum.
http://forums.bimmerforums.com/forum....php?t=1870727

[Alaric Darconville]

There is a thread in a BMW forum asking the same question and it has created a sort of disagreement. My opinion is that the power consumption is the same but the light output is modified by the reflector. A gentleman who has worked for the BMW suggests that they are modified by the BMW.

I used to work for Wendy's, but I couldn't tell you what machine they use to deep fry the chicken for their sandwiches, because things may have changed since then.

I expect that for both high and low beam applications, the nominal wattage is the same. If they wanted different wattages for high and low beams, using two different bulbs would be better.

[Hilldweller]

I believe that the E90 has PWM'd circuits ---- does the car in question have DRLs? That would be the only change in power to speak of that I know.
You'd have the same amperage at nominal output to both the high and lowbeam.
FWIW, I like H7s if you're using good ones. I used to use Osram 65w bulbs in my Honda Goldwing and MINI Cooper R53; the light was quite nice. Those bulbs were the original Silverstars, not to be confused with the miserable Sylvania product.
Your highbeams on the car just have a different reflector, aim, etc than the lowbeam.

[Scheinwerfermann]

The idea of supplying different voltage to the bulb for the low vs. high beam function is only just very recently allowable by the applicable regulations; late last year ECE Regulation 37 was amended to provide output ratings for headlight bulbs at both 12v and 13.2v. This, together with a few other changes in the applicable regulations, now permit the homologation of an optimized BiHalogen headlamp (a projector with a movable cutoff shield which produces a low beam until the cutoff shield is moved electrically out of the light path, then it provides a high beam). The optimization consists of using a high-luminance, high-flux bulb, such as H9, operated at 12v with cutoff shield in place for the low beam function and 13.2v with the cutoff shield stowed for the high beam function. This optimizes bulb lifespan on low beam and bulb luminance and flux on high beam. A couple of the major European headlamp makers have proposed such projectors, but TTBOMK no automaker has yet commercialized such a headlamp.

The idea is not used in single-beam headlamps (low beam only, high beam only). All BMWs presently on the road with halogen headlamps supply line voltage to the low beam bulbs and line voltage to the high beam bulbs. And there are no "low beam H7" versus "high beam H7" bulbs; they are the same. The difference in light distribution is entirely due to the optics.

UPDATE: I just skimmed the linked thread. The guy talking about PWM operation is technically correct; BMW has made extensive use of PWM supply to exterior lights for some years now -- for example, dimmed high beams as DRLs, single-filament P21W bulbs operated at full voltage for the brake light mode and at PWM low voltage for the tail light function, etc. They may run the headlamps via a PWM-controlled steady-voltage supply to assure maximum bulb lifespan. But they do not operate the bulbs at one voltage for low beam and another for high beam.

[SemiMan]

The idea of supplying different voltage to the bulb for the low vs. high beam function is only just very recently allowable by the applicable regulations; late last year ECE Regulation 37 was amended to provide output ratings for headlight bulbs at both 12v and 13.2v. This, together with a few other changes in the applicable regulations, now permit the homologation of an optimized BiHalogen headlamp (a projector with a movable cutoff shield which produces a low beam until the cutoff shield is moved electrically out of the light path, then it provides a high beam). The optimization consists of using a high-luminance, high-flux bulb, such as H9, operated at 12v with cutoff shield in place for the low beam function and 13.2v with the cutoff shield stowed for the high beam function. This optimizes bulb lifespan on low beam and bulb luminance and flux on high beam. A couple of the major European headlamp makers have proposed such projectors, but TTBOMK no automaker has yet commercialized such a headlamp.

The idea is not used in single-beam headlamps (low beam only, high beam only). All BMWs presently on the road with halogen headlamps supply line voltage to the low beam bulbs and line voltage to the high beam bulbs. And there are no "low beam H7" versus "high beam H7" bulbs; they are the same. The difference in light distribution is entirely due to the optics.

UPDATE: I just skimmed the linked thread. The guy talking about PWM operation is technically correct; BMW has made extensive use of PWM supply to exterior lights for some years now -- for example, dimmed high beams as DRLs, single-filament P21W bulbs operated at full voltage for the brake light mode and at PWM low voltage for the tail light function, etc. They may run the headlamps via a PWM-controlled steady-voltage supply to assure maximum bulb lifespan. But they do not operate the bulbs at one voltage for low beam and another for high beam.

Scheinwerfermann, I always learn things from your posts. Thank you!

Semiman

[Scheinwerfermann]

Thanks for the acknowledgement. You are welcome!