Date:         Sun, 29 Jun 1997 14:09:37 -0700
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Blue Eyes <lvlearn@ibm.net>
Subject:      Old alternative driving light proposal reviewed

I'd read that high-end Audi and BMWs had gas discharge headlamps earlier, 
so while reading about the new VW Passat, I found the following clip 
interesting.

***********copy follows************

 Gas-discharge headlamps emit 2-1/2 times more light than conventional
 halogen-bulb units.  The source of light is a glass lamp filled with
 xenon gas.  The gas is ignited by a high-tension electric pulse
 generated in a special supply unit.  Xenon lamps run for about 2,500
 hours or four times as long as the average halogen bulb.  The new
 Passat is the first Volkswagen to have this form of lighting as a
 factory option.

************end copy************

I've followed evolving driving light improvements for 4 decades now and 
confess to having used high amperage aircraft landing lights nearly as 
long ago, as well as having performed lots commercial product trials.  
These Xenon lamps sound to me like an appropriate solution.  You're 
already familiar with Xenon lamps' excellent color temperature.  They've 
been used in photo flash units for years.  Few VW Bus drivers enjoy 
really good driving light systems, and some originally equiped VW Van 
lighting systems borderline on being dangerously inadequate.

The old suggestion of polarizing driving light output and similarly 
polarizing the driver's night view still appeals to me, though I 
understand the DOT has never approved it for use on US roadways.  As I 
understand it, part of DOT staff's objection to the proposal was 
reduction to already limited light output available from then current 
lamps that auto electrical systems could sustain.

Consider your whole lighting system designed to substitute for natural 
illumination at dark times (did you think I was going to say "night," 
hereby failing to consider eclipses?).  You send out visible radiation 
and depend on what's reflected back to make driving decisions on which 
your family's life may depend.  Obviously the better your 
information/noise ratio, the better your decisions.  The implications are 
clear.

Imagine your vehicle is both send/receive polarized on the top left to 
bottom right axis of X, and so are vehicles approaching you from the 
opposite direction.  You clearly and brightly see your own reflected 
illumination.  But similarly equiped on-coming traffic illumination 
appears to you to be polarized on the bottom left to top right axis, so 
their driving lamps don't brightly glare information "noise" into your 
eyes.  X pattern polarized illumination is very clever and very 
appropriate if the supporting equipment exists.  I suggest that time is 
finally at hand.

The first obvious concern about any new system is backward compatibility 
with prevailing standards.  By increasing lamp output, then through 
polarization, proportionally decreasing it to the current DOT allowable 
maximum, no other drivers would be negatively impacted by the appearance 
of this new standard on US public roadways.  But drivers and passengers 
of other polarized illumination system equiped vehicles would be 
positively impacted.  So the backward compatibility test appears 
positive.

Another concern is electrical load sustainability.  Two convergent 
changes have worked to our benefit here.  Gas discharge lamps like Xenons 
and metal halides are much more efficient in converting electrical energy 
into visible radiation than halogens that were "state of the art" a 
quarter century ago.  Times change, and with them so too have typical 
motor vehicle electrical systems.  Larger sustainable load carrying 
capacity is common in cars today than when big fins were popular.  

An even smaller metal halide gas discharge lamp for battery pack equiped 
bicyles is now available.  It's 21 watts produce light equivelant to a 
conventional auto headlight!  Granted, they're priced like moon rocks, 
but with near zip production volumes, new technologies tend to be that 
way.

Anyway, I hope this sparked some interest.  If the DOT got enough 
requests to reevaluate the X pattern driving light polarization proposal 
again in the context of today's new more efficient lamps and improved 
electrical systems, perhaps we might foster a more pleasant tomorrow and 
save a few lives at the same time.

If you feel this posting should be reviewed by other eyes and you 
subscribe to other appropriate e-mail lists or similar information 
exchange facilities, feel free to "cut and paste" parts of it as you see 
fit into a contribution for their eyes.  There's no need for attribution 
to me as my only objective here is to make tomorrow better. 

Thanks for your consideration and the best to you all,
Blue