LED Light Emitters: Failure Mode?

[(PeteCresswell)]

Do LED lights fail completely or gradually?

i.e are they all-or-nothing?

I've got a nice little LED flashlight that, one day, started
getting dim.

Noticed that some of the contacts were corroded and wire-brushed
the ones on the back of the emitter module. The plate that
connects the two stacks of AA batteries in the back recess of the
light's body is inaccessible so, after scratching it a little
with a long knife to no avail, I folded up some alu foil and
stuffed it down there... but still no luck.

Fooled around with it today, and couldn't even get a dim light by
applying 6v from a known good source to the feet of the emitter
module.

My first thought was that I'd hosed the LED completely by
accidentally applying reverse polarity somewhere along the line.
Possible?

If not, what about the gradual dimming? Does that fit with LED
failure, or does it narrow the cause down to some sort of
electrical contact issue?

 

[Meat Plow]

Do LED lights fail completely or gradually?

i.e are they all-or-nothing?

I've got a nice little LED flashlight that, one day, started
getting dim.

Noticed that some of the contacts were corroded and wire-brushed
the ones on the back of the emitter module. The plate that
connects the two stacks of AA batteries in the back recess of the
light's body is inaccessible so, after scratching it a little
with a long knife to no avail, I folded up some alu foil and
stuffed it down there... but still no luck.

Fooled around with it today, and couldn't even get a dim light by
applying 6v from a known good source to the feet of the emitter
module.

My first thought was that I'd hosed the LED completely by
accidentally applying reverse polarity somewhere along the line.
Possible?

If not, what about the gradual dimming? Does that fit with LED
failure, or does it narrow the cause down to some sort of
electrical contact issue?

An LED can grow dim if the input voltage is too high but I've never heard
of one gradually dimming. This does not mean that it doesn't happen of
course.

 

[Ron(UK)]

An LED can grow dim if the input voltage is too high but I've never heard
of one gradually dimming. This does not mean that it doesn't happen of
course.

I have several of those little led keyring torches, and they do grow
dimmer after a time compared with new ones even with brand new batteries.

Ron(UK)

 

[Meat Plow]

I have several of those little led keyring torches, and they do grow
dimmer after a time compared with new ones even with brand new batteries.

Cheap Bastards, how dare they!

 

[mc]

Gradual dimming is the normal way LEDs wear out. I thought it took years,
though.

 

[Keith G]

Cheap Bastards, how dare they!

OK, Meat Wanka - we're in your parlour now. Let's see what Mr Big Mouth
Show-Off's like when he's at home....

(I'll be in touch soon, sweedie.... ;-)

 

[Michael Kennedy]

Gradual dimming is the normal way LEDs wear out. I thought it took years,
though.

If you overdrive them it will happen much faster. I've done that a few times
playing with LEDs.

Mike

 

[Trevor Wilson]

Do LED lights fail completely or gradually?

i.e are they all-or-nothing?

I've got a nice little LED flashlight that, one day, started
getting dim.

Noticed that some of the contacts were corroded and wire-brushed
the ones on the back of the emitter module. The plate that
connects the two stacks of AA batteries in the back recess of the
light's body is inaccessible so, after scratching it a little
with a long knife to no avail, I folded up some alu foil and
stuffed it down there... but still no luck.

Fooled around with it today, and couldn't even get a dim light by
applying 6v from a known good source to the feet of the emitter
module.

My first thought was that I'd hosed the LED completely by
accidentally applying reverse polarity somewhere along the line.
Possible?

If not, what about the gradual dimming? Does that fit with LED
failure, or does it narrow the cause down to some sort of
electrical contact issue?

**White LEDs wear out pretty quickly. They are a blue LED with a fluorescent
coating. The coating fails. Regular coloured LEDs can last for many decades,
whilst I've found white LEDs will dim to around 30% of their original output
after about 1 - 2 years of continuous duty (at rated current). Higher
currents will accelerate that wear.

Trevor Wilson

 

[Andy Cuffe]

If you overdrive them it will happen much faster. I've done that a few times
playing with LEDs.

Mike

I have some blue Philips LED christmas lights that I was using as a
night light. After they were on 24/7 for a year a number of LEDs had
failed short circuit and the rest were 50-75% dimmer than new. I was
very disappointed with them. Ordinary light bulbs last longer than
that! They were either using cheap LEDs, or over driving them (or
both). Looking directly into the dim LEDs I could see large dark
areas on the dice.
Andy Cuffe

[email protected]

 

[Arfa Daily]

**White LEDs wear out pretty quickly. They are a blue LED with a
fluorescent coating. The coating fails. Regular coloured LEDs can last for
many decades, whilst I've found white LEDs will dim to around 30% of their
original output after about 1 - 2 years of continuous duty (at rated
current). Higher currents will accelerate that wear.

Trevor Wilson

I believe that some of these LED flashlights use drive electronics built
into the head, to pulse the LEDs rather than DC drive them. It apparently
produces a greater light density per amp, and helps to prolongue the life of
the LEDs. It's possible that the one that has failed may have such
electronics, and that's where the problem lies ??

Arfa

 

[William Sommerwerck]

I have some blue Philips LED christmas lights I was using as a
night light. After they were on 24/7 for a year, a number of LEDs
had failed short-circuit, and the rest were 50-75% dimmer than
new. I was very disappointed -- ordinary light bulbs last longer than
that! They were either using cheap LEDs, or overdriving them (or
both). Looking directly into the dim LEDs I could see large dark
areas on the dice.

Don't do that! You'll put your eye out!

 

[Allodoxaphobia]

Don't do that! You'll put your eye out!

Maybe _that_ explains the "large dark areas ...."

 

[Trevor Wilson]

I believe that some of these LED flashlights use drive electronics built
into the head, to pulse the LEDs rather than DC drive them. It apparently
produces a greater light density per amp, and helps to prolongue the life
of the LEDs. It's possible that the one that has failed may have such
electronics, and that's where the problem lies ??

**Certainly possible. However, it depends on the electronics driving the
LED. Manufacturers have a tendency to drive the LED as hard as possible, in
order to obtain maximum brightness. They don't care if the thing fails in
six months. The money is already in the bank.

Trevor Wilson

 

[Meat Plow]

OK, Meat Wanka - we're in your parlour now. Let's see what Mr Big Mouth
Show-Off's like when he's at home....

(I'll be in touch soon, sweedie.... ;-)

Yawn-------

 

[Keith G]

On Sat, 19 Jan 2008 21:43:50 +0000, Keith G wrote:


Yawn-------

Aww.....

Meat Wanka's tired - must be past his bedtime! (Perhaps he should try
wearing boxing gloves at night - then he'd not be so *beat up* during the
day!

At least his tits aren't still slapping the keyboard....

 

[James Sweet]

Do LED lights fail completely or gradually?

i.e are they all-or-nothing?

I've got a nice little LED flashlight that, one day, started
getting dim.

Noticed that some of the contacts were corroded and wire-brushed
the ones on the back of the emitter module. The plate that
connects the two stacks of AA batteries in the back recess of the
light's body is inaccessible so, after scratching it a little
with a long knife to no avail, I folded up some alu foil and
stuffed it down there... but still no luck.

Fooled around with it today, and couldn't even get a dim light by
applying 6v from a known good source to the feet of the emitter
module.

My first thought was that I'd hosed the LED completely by
accidentally applying reverse polarity somewhere along the line.
Possible?

If not, what about the gradual dimming? Does that fit with LED
failure, or does it narrow the cause down to some sort of
electrical contact issue?

It depends on the LED, some of them do in fact grow dim, the blue LEDs on my
PC used to be identical, now the hard drive LED is considerably brighter
than the power LED which is on far more. The phosphor coated LEDs dim even
faster, white and pink LEDs are a phosphor over a blue chip.

I've had some too that got dim and flickered. I don't know the exact
mechanism of failure.

 

[James Sweet]

I have some blue Philips LED christmas lights that I was using as a
night light. After they were on 24/7 for a year a number of LEDs had
failed short circuit and the rest were 50-75% dimmer than new. I was
very disappointed with them. Ordinary light bulbs last longer than
that! They were either using cheap LEDs, or over driving them (or
both). Looking directly into the dim LEDs I could see large dark
areas on the dice.
Andy Cuffe

I have some too that have bad LEDs, they flickered horribly as well, one set
I modified with a rectifier and it was MUCH nicer looking then, it lasted a
couple years but now has one dim flickering LED. My friend gave me some more
sets which had not been modified and they have several more bad LEDs so it
isn't the rectifier that did it. I'm not impressed with LED Christmas
lights, they're just not there yet.

 

[William Sommerwerck]

I have some too that have bad LEDs, they flickered horribly as well,
one set I modified with a rectifier and it was MUCH nicer looking then,
it lasted a couple years but now has one dim flickering LED. My friend
gave me some more sets which had not been modified and they have
several more bad LEDs so it isn't the rectifier that did it. I'm not impressed
with LED Christmas lights, they're just not there yet.

What you're saying suggests that the LEDs are simply connected across the
power line in series, with the LEDs serving as their own rectifiers, so to
speak. Glitches and spikes in the "reverse" direction aren't going to do the
LEDs any good. Adding a rectifier presumably provides protection.

 

[Jimmie D]

I have some blue Philips LED christmas lights that I was using as a
night light. After they were on 24/7 for a year a number of LEDs had
failed short circuit and the rest were 50-75% dimmer than new. I was
very disappointed with them. Ordinary light bulbs last longer than
that! They were either using cheap LEDs, or over driving them (or
both). Looking directly into the dim LEDs I could see large dark
areas on the dice.
Andy Cuffe

[email protected]

They probably were being overdriven. I have some blue LEDs that are on 24/7
now for 3 years without any sign of dimming. 2 of then make an excelent
bathroom night light. I reccomend using a small transformer to step the
voltage down to something close to the value they need. The LEDS will still
have to draw there rated current if you use a resistor to drop the voltage
from 120 you might as well use a light bulb instead of an LED.