On Sat, 7 Apr 2007 08:28:07 -0500, "Anthony Fremont"
wrote:

MassiveProng wrote:
On Fri, 6 Apr 2007 08:10:25 -0500, "Anthony Fremont"
Gave us:

We will have to see on that. It sure looks like they're burning out
in traffic signals and car tail lights fast enough.

That's bull****. Bus Lines, as well as traffic controllers switched
to them SPECIFICALLY due to the FACT that they have a longer life
span, and lower consumption rate.

And you don't see failures? Take a good look at traffic lights, you can
usually find dead pixels in them. They might last longer, but they aren't
eternal.

---
Good quality LEDs have lifetimes in excess of 50000 hours with, I
believe, the criterion for failure being a halving of the light
output.
---


On a slightly different note, I'm disturbed at the number of vehicles I see
that don't have working tail lights. Not old vehicles, but newer ones (3
years old) that shouldn't have these kinds of failures. It looks to me like
over-all reliability is going the other way while expense and complexity are
going up. I know those failures are for other reasons, but they are
failures none the less.

---
I suspect that in cars, early LED failure is due to the nasty
electrical environment, and primarily to high-voltage reverse bias
spikes PIVing the diodes.
---

The light source will be
expensive and it will have a limited life (man-made at least).

Bulbs yes. LEDs, no. That stats already exist.

Like always, they will be operated at the maximum power dissipation that
gives a life expectancy just longer than the warranty period. Why do you
think it would be any different? Just look at regular light bulbs, a 10%
reduction in voltage greatly increases life expectancy. Given that, it
stands to reason that manufacturers could just make the filament a little
sturdier to accomplish the same thing. Why aren't any manufacturers doing
that?

---
Make the filament any thicker (sturdier, but lower resistance) and
you'd need a lot more power to get the same brightness as well as
making the lamp cost more. Make it any thinner (less sturdy and
higher resistance) and you'd have to make it shorter and it would
burn out more quickly.

The failure mode for the lamp (other than gross mechanical abuse) is
evaporation of the tungsten from the filament to the point where the
filament can no longer support its own weight and it breaks.

There is no such failure mode in an LED. See "Failure Modes" in:

http://en.wikipedia.org/wiki/Light-emitting_diode


--
JF