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Home About RSR Taste of the Past Rendez-vous February 1999 - Blue Light Special

Rendez-vous February 1999 - Blue Light Special

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RSR Rendez-vous February 1999


Blue Light Special

I'm writing this in the "dark" part of the year, you know, it's 
dark when you go to work and it's dark a couple hours after lunch. Our
headlights get a workout until the days get longer. I mentioned
Litronic headlamps in my last rant about fog light misuse and I've
gotten email about them. 

You've probably seen cars equipped with these lights. They're easy to
spot. The headlights are very bright and when viewed from the front, 
so
white as to make regular headlamps look yellow. Seen from a more 
oblique
angle, they look blue. Porsche fits them as standard equipment on the
Turbo and Turbo S models and they're optional on others. They are
expensive as you may have noticed.

These lamps are also available on lesser brands like Mercedes, 
BMW and
Lincoln. Each manufacturer has their own name for them but they
essentially use the same technology. What makes them special is 
their
high efficiency, remarkable light output and spectrum.

As a class, these Litronic, Xenon etc. headlights are High Intensity
Discharge (HID) lamps. They've been used for years lighting parking
lots, arenas and ski-hills. You may recognize trade names like
"Metalarc" for instance. 

HID lamps are very popular for illuminating large areas with 
a minimum of lamps. The reason is simple. These luminaires 
produce a ton
of light per watt of power consumed and the "bulbs" last a long time, a
good thing, considering they are fairly expensive. I quoted "bulbs"
because I have a hard time calling a lamp which can cost hundreds of
dollars a "bulb". The output tends towards the higher frequency or
"blue" end of the spectrum. Ladies, don't try on bathing suits under
this light. 

HID produces light by exciting an arc. A gas (usually Xenon) 
is charged by a high voltage making it glow. Regular lights are 
incandescent, i.e., they produce light by heating a filament of metal
until it glows. Sooner or later the filament burns thin and fails. HID
lamps don't depend on a filament and are much more durable.

In order to induce a gas to glow brightly (that's the arc) you have to
use very high voltage, usually in the range of 30,000 volts or more. 
The input voltage is converted to a higher voltage using a transformer.
In the lighting business, they call them "ballasts".

Until recently, HID lamps took too long to start to make them 
useful in automotive applications. What's made HID practical 
for cars was the invention of the electronic ballast. Instead of 
using transformers and large capacitors, a small electronic circuit can
be used to take a low input voltage and change it into a much higher
output. 

The electronic ballast is smaller, lighter and best of all, much 
faster to build up enough voltage to create the arc. Voila, the 
vehicular solution. 

In automotive service HID headlamps offer significant benefits. They are
far more efficient than halogen lamps. A 35 watt lamp is all that's
needed to produce the stunning light output of a 993 Turbo. Compare
that to 55 watt halogen lamps with less output and you'll see that 70
watts per pair is a serious energy saving compared to 110 watts for
halogen lamps. Drawing less power from the alternator results in fewer
gallons burned or, in the case of a 911, less engine output wasted on
producing amps instead of acceleration. 

HID headlights cost a lot. About $2,000 on a 911, and around $1,200 on a
Bimmer. While the lamps (aka bulb) and the electronic ballasts are
costly, the biggest expense is the improved optics. Along with the
high-tech bulbs we get much better reflectors and lenses. If you test
drive a Porsche with HID headlamps, you'll notice that the light pattern
is very precisely controlled.

Sophisticated optics are worth the effort when using HID 
because the lamp itself contributes to the process. The arc is 
very small and precisely located. The small source and accurate 
location (consistent from lamp to lamp) means that the lens and 
reflector assembly can be optimized instead of compromised. We've 
come a long way since the days of a checker board pattern stamped 
into the glass of a sealed beam lamp.

Did you notice the blink? When you turn on HID headlights, you'll see
what looks like a momentary blink. Look more closely and you see that
two things are happening. First, the arc lights off and for a split
second the light output is low. About two-tenths of a second later, the
lamp is at full brightness. While this is going on, the headlamps are
adjusting themselves to level! Since they're so bright, automatic
aiming makes a lot of sense. 

I haven't quite figured out how it works. I suspect a liquid and
some sensors which operate a servo mechanism. Does this sound more
expensive than a couple of adjusting screws? I remember my old
Renault, under the hood were a couple of levers which adjusted the
aim (up and down) of the headlights. You could compensate for the
load. Good thing too because they had very soft, long travel
suspensions and with a good load in back the headlights would be
illuminating tree tops. 

Of course you can always count on Porsche to engineer a superior 
solution. The latest Litronics on the 996 not only self level but 
compensate for the terrain. They dip going up hill and rise going down.
Since they are so bright, avoiding dazzle for oncoming drivers is a
very nice feature. On cars without this gadget, you're likely to get a
face full of high beams as a sign of how much the oncoming vehicles
appreciate your high tech lights. 

One Bulb Fits All:

There's a lot going on in automotive lighting. Designers are working
hard to produce a practical single source system. A single HID lamp in a
convenient location would provide all the lighting needed for the car.
Headlights, turn signals, instruments, switches and courtesy lights, the
whole works all lit from a single source. 

Distribution will use fiber optics. Before you laugh at the notion,
consider how much of a car's wiring harness is there to support
accessory lighting. Those harnesses are expensive, trouble prone and
heavy. Optical fiber pipes are almost indestructible and can be routed
anywhere inside or underneath the car. There are no connections to
corrode and no bulbs and/or sockets to replace. If you've ever suffered
the frustration of having to dismantle the entire dash to replace a
lousy indicator bulb you'll like where the industry is going.

The idea of reducing weight and complexity of a car's electrical 
system by using new methods is not new. Modern car designs use a "bus"
instead of individual wires to each controlled element. Aircraft have
been doing this to save weight for years. On a 747 there is a single
pair of wires that connect all the reading lamps together. A tiny
electronic circuit attached to the wiring at each lamp is told by a
computer to turn on or turn off the lamp. When you push the "on button"
a signal is sent to a controller somewhere which responds with a signal
to the control circuit to connect the lamp to the power bus. These
signals are sent on the power bus wiring itself. This explains why
there is a slight delay between the time you press the button and when
the light actually turns on, if you've ever wondered.

I'm told that these devices save over 10,000 pounds of electrical 
wire on a jumbo jet. This system is showing up in automobiles and I
think we'll see more and more of this as designers try and reduce weight
and make cars more reliable and easier to maintain.

Dazzling Technology:

After my rant about %$#$ fog lights last month, someone passed me an
article about a pilot project being run by Hella and Volvo. The idea is
to use polarized headlights and coat the windshield with a partially
reversed polarity coating. When light is reflected its polarity changes
so that (in theory at least) the light coming back from the road surface
in front of you would be visible. Direct light from the lights of an
oncoming car for example would be reduced by virtue of the coating on
the glass since the direct light would be of reversed polarity. A neat
idea if it works. Until these things are available, I think we should
polarize fog lights by spraying them black.

Yet another idea is to use lamps with a much higher proportion of UV
light than visible. UV is that so called black-light which makes your
white shirt appear to glow in the dark. The notion is that it will
provide plenty of usable light for the driver while being much less of a
nuisance to oncoming cars. I suspect it would defeat the purpose of
daytime running lights though. 


Bob

Porsche ... lighten up, spring is coming.

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