[s-cars] Re: HEADLIGHT UPGRADE

[Kirby Smith]

In reading the following, admittedly in haste, I got the impression of a
misconception about lamp radiant output behavior.

The original comment asserted that by adding xenon gas to the
tungsten-iodide (halogen) cycle, a higher color temperature could be
achieved for the same wattage.  I don't know if that is particularly
true, but just adjusting the filament will do the same thing at the
expense of lifetime, so presumably the actual effect, if true, is
increasing the color temperature at the same lifetime.

At a higher color temperature, more of the lamp emission is provided in
the visible band and less is generated in the part of the IR band where
the quartz envelope absorbs, roughly 2.7 microns and longer.  In this
case, with the assumed same wattage, the quartz would run cooler, and so
would the base.  However, the halogen cycle depends on the quartz being
hot enough for the iodine to pull the tungsten off the surface and
redeposit it back on the filament.  (It does this imperfectly, else the
lamp lifetime would be infinite.)  A smaller envelope could compensate.
Thus I suspect such lamps operate very nearly with the same thermal
behavior as regular halogen lamps.

Assuming such lamps have no deliberate spectral filtering, do they
advertize an apparent black body color temperature?  Normally, halogens
are operated in the range of 3200K to 3400K.  Audi wiring is so good at
degrading voltage that I suspect they barely reach the minumum.  This
would explain why I very rarely have to change a headlamp in any of my
three cars.  (Tungsten lamp lifetime goes as the inverse of some high
power of the voltage.)  If one were willing to change his lamps twice a
year, he could run at 14V - 15V and get a lot of improvement in color
temperature for a modest increase in power load.  The power supply
needed for this would possibly approach the cost of an HID setup, so I'm
not proposing it as really practical, although the intermediate step of
relaying the headlights provides a clear improvement, at least for
90qs.  (I haven't done the S6 yet.)

So, the actual questions to be asked of a candidate lamp are: What is
your color temperature, at what input power (at 13.6V, say), and at what
lifetime?  Unless the candidate lamp's color temperature went up
relative to the baseline lamp without increasing power or degrading
lifetime, then there has been no technological improvement, just a
different choice of operating point.  Or ask the simpler question: How
many lumens do you output at what lifetime?  That answer will compensate
for the eye's response.  Indoor lighting is specified in that manner.

kirby

CyberPoet wrote:
>
> Dan,
>
>     What you are missing is the temperature issue (above and beyond it
> drawing the same power). Any
> given filliment can be made to run brighter by improving it's burn
> characteristics. Up the temp of the burn
> on any specific type of bulb (by either increasing power or decreasing
> filiment width), generally up the light output,
> but simultaneously increase the heat that is radiated from the quartz
> surface of the bulb as infrared heat.
> Increasing the ambient bulb casement temperature leads to a
> higher-than-designed-for temperature in the headlight housing, which
> over time causes the plastic components to fail by either becoming
> fragile (heat range cycling) or melting (too high
> an absolute temp). Additionally, since the reflector material sits on a
> plasticized backing in your car, that plastic
> may well also give up it's surface cohesion, resulting in loss of
> reflective materials. Increasing the power to the
> bulb (using a higher-draw bulb) adds to all the previous problems by
> increasing the heat load on the supply wires and
> relays, which in worst-case scenarios can lead to fire (gee, imagine
> that next time you're driving through the country
> on a deserted road at night).
>
> Everyone here pretty much gave you the best advice on what to do with
> the stock headlight system -- replace it with
> the Euro lens or the Euro-spec headlight assemblies. The only
> additional suggestion they missed I will take straight out of my own
> rally experiences and add to their advice: add an additional set of
> externally mounted driving lights (such as Hella 550's mounted below
> the bumper line). Since these lights won't tie into the existing wiring
> harness, you can buy as powerful a set as you can stand (and afford --
> low cost Hella's can be had at $60 set for driving lights) -- and
> simply add more light by a factor of 100% or more rather than trying to
> upgrade your existing lights by a factor of 10% - 35%.
>
> Best Wishes,
> =-= Marc Glasgow
>
> Dan said:
>
> > I am considering just replacing my stock
> > bulbs with Xenon bulbs, which are available at
> > http://www.eurolights.com/.
>
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