Re: LED "bulbs" for Spider tail lights

["Dean W. Cains" <dwc@domain.elided>]

Hi Paul:

You're exactly correct in your reasoning about why the LED 'bulbs' aren't 
yet perfected for cars.  If the LED's were facing into the reflector, 
they'd be plenty bright and probably work well, as the ones I bought are 
not really lacking in absolute light output.  They have a dozen or so LED's 
in each 'bulb'.  Unfortunately, they were likely designed for the rice-boys 
with their clear tail light lenses, and not for real cars.  FWIW, I've seen 
buses and trucks with purpose-built LED tail lights that seem to work very 
well, and one of the new Cadillacs has rear lights that must have 100 LED's 
in a circuit board just inside the lens,  Those work pretty well, but if 
you view them from an angle too far off-axis, the light output drops off 
considerably.  Also, I find that the instant-on quality of the LED's seems 
to attract my attention better, which is exactly what I wanted my Spider's 
brake lights to do.

I remember a product described in Road & Track maybe 30 years ago that was 
interesting.  It was called the Cyberlight and it had a short, wide lens 
that mounted along the top edge of the rear license plate.  The light was 
activated by the brake pedal, but had an accelerometer built into the 
circuit as well.  Higher rates of acceleration (during braking) resulted in 
the light flashing at a faster rate, which was supposed to attract more 
attention.  As I recall, they were tested on a fleet of NYC taxi cabs, and 
the rate of rear end collisions decreased by some impressive number, like 
40%.  Maybe a good idea that got neglected by NHTSA and/or DOT, or maybe 
the Cyberlight inspired the center brake lights we all have now.  Who 
knows?  I do know that I've almost always got one eye on my Spider's rear 
view mirror when I'm stopped at an intersection.  I happen to have a NOS 
Cibie rear fog light (red lens) that is almost blindingly bright, and I 
guess I could always give that a try as a third brake light.

Regards,

Dean


At 05:32 PM 11/22/2002, you wrote:

> Date: Fri, 22 Nov 2002 10:43:35 -0800 (PST)
> From: Paul Witek <pwitek@domain.elided>
> Subject: Re: LED "bulbs" for Spider tail lights
>
> I think the primary problem with these LED "bulbs" is that they're trying 
> to replace incandescent bulbs in a taillight designed for incandescent bulbs.
>
> Light bulbs are a "point source"; that is, without reflectors, the light 
> travels pretty much in all directions from the filament.  Taillights use 
> reflectors to shine the light from the sides of the bulb out through the lens.
>
> LEDs are far more directional; by and large there is very little light 
> leakage off to the sides.  Without this, you end up with a small circle of 
> illumination on the lens, right over the bulb.
>
> Add to this fact that as yet, even the brightest LED's are a far cry from 
> putting out the light of a 79-cent 1156 bulb.  New production cars that 
> use LED's in the taillight use a large array of them (with no reflectors).
>
> I suppose one could mount a ton of individual LEDs on some perf board (or 
> etch a circuit board) the same shape as the lens of a taillight - this 
> would put out much closer to the original light output and pattern.
>
> You can always spot cars with LED taillights, they're somewhat odd in that 
> the light is on, then instantly off - you don't realize how conventional 
> bulbs "fade out" as the filament cools until you see an LED taillight 
> switch off.
>
> - - Paul Witek
--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided