RE: Red dash gone

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

... a few thoughts ...

... you could have 1000+ watts of light facing away from you ... unless it
reflects from something it will not affect your night vision ...

... it may be true that the reflection of said source from some object on or
in your path could be bright enough to affect your night vision, but unless
that object is a mirror that is aimed directly back into your eyes the 1/r^2
rule should apply to the returned light.  In any case, this is the reason
you want that kilowatt of illumination ... to see what is ahead.  

... you are correct that the big reason behind the use of the red
illumination is that the pupil responds least to such wavelengths of light
... and it sure seems to me that you have answered your own question.  The
goal is to provide the best chances that you will be able to see the objects
outside of the car that you need to see to safely operate your vehicle.  To
achieve this you attach the brightest illuminator to the front of your car
to increase the chances that some light will reflect off the important
features outside, and you minimize the illumination inside the vehicle as
much as possible and make it an appropriate wavelength to minimize the
amount of pupil restriction which would limit that light being returned from
the outside world.  Certainly your pupils will adjust to the reflected light
if it is bright enough.  

When this thread comes up it always calls to mind that one night driving in
California's Sierra Nevada mountains on a brightly moonlit night.  Once your
eyes had adjusted to the darkness visibility was much better driving with
the headlights turned off!  Fortunately we were the only one on the road so
it wasn't necessary to deal with eyes adjusting to oncoming headlamps.  

Steve Buchholz
San Jose, CA (USA)

... hey, isn't that a blue moon rising right about now?  :-)

	----------

	This doesn't make sense.  My 200+ watts of white light illuminating
the 
	road in front of me don't affect my night vision?  By the same
thought 
	process as long as I don't look _at_ the sun, just the lit results,
then 
	even daylight wouldn't affect night vision.  Yes, I am aware of
being 
	blinded by other drivers, but that affect would be similar to
staring at 
	the sun (don't please) briefly and then having diminished vision for
a 
	period in normal light.  This is due to the adjustment of the pupil,
not 
	the eye chemical that gives night vision.  I know that red light 
	preserves night vision, I just question whether red dash lighting in
a 
	vehicle relying on bright white lights for forward vision serves
that 
	purpose.  BTW, I like my red dash lights.