Re: LED's

[Lance Fisher <lfisher@cyberoptics.com>]

Been following the posts on LEDs and wanted to set some
things straight that might have been a
little misleading.
 First while it's true that incandescents are much less
efficient than LED's I doubt that the heat from incandescent
stop lights does much for melting snow and ice.  I live in
Minnesota where it gets pretty cold and my taillights get
covered with snow often.  Also unless you drive with your
foot on the brake all the time (and way too many do around
here, but not for that reason) the brake lights won't be on
long enough to warm anything.
 Second it is not true, as one poster suggests, that "LED's
are many times more efficient
when pulse-driven at higher voltages".  LEDs (and their
cousins  Laser Diodes) are often used in a pulsed mode but
this does not in any way allow higher average brightness.
Pulsed drive is used for the following two reasons:  Short
high intensity pulses are easier to detect by electronic
photo detectors under some circumstances and pulsing the
light allows the carriage of useful information on the light
signal.  A much more common reason which probably applies to
stop lights is that to limit the current passing through an
LED to a life prolonging value pulsing  makes the driver
much more efficient which translates into less heat
dissipated by the driver and a longer life for it.
BTW around here they have begun to use LEDs for traffic
signals.  First only for the red lights but lately the
greens are LEDs also.  I'm pretty sure long life is the main
incentive.  If you are looking for this it is pretty easy to
notice... check it out.

lance fisher
lfisher@cyberoptics.com
93 S4

P.S. While I may think I know a lot about LEDs (I design
electronics involving LED's and Lasers) I am kind of
ignorant about some aspects of Audi's.  What exactly does
UrQ mean?  I assume that the Q stands for quattro.