Do LEDs become older after being used for 1 year?

[Q Gang]

Hi

I found a strange things in my LEds device.

I made a "Batterless Bicycle Safety Lights" 12 months ago.
(http://www.freelights.co.uk).

The LEDs on the device are opened to the air, sometime raining, water
will touch the LEDs. Few days ago I found the red LEDs not working. I
checked all system, nothings is broken. Then I uses a 3v battery to
test the LEDs, the LEDs are working, but I feel the red LEDs are
little darker than the new LEDs. When I put the red LEDs back to the
device, the red LEDs still not working.

Finally, I change the red LEDs (replaced by 2 new red LEDs), the
system working again.

The problem is: Will the LEDs become older after using a while? Such
as become darker, resistence will go up.....

Someone who are know LEDs well can give me a answer. Thanks very much.

This is very important to me, because I plan to mass manufacturing
this product in low cost. If the LEDs will become older, I have to
change the designs for mass manufacturing. (To be honest, I do not
know how the do the redesign job if the LEDs do get older).

If you are interested see my redesign works for mass manufacturing, go
to:
http://www.helpyou.freewire.co.uk/redesign.html

Thanks for your help.
Chin

 

[Spehro Pefhany]

On 28 Oct 2004 06:50:40 -0700, the renowned [email protected] (Q Gang)
wrote:

Chin:-

Especially some cheaper white LEDs will lose brightness after a long
time operating near maximum current, but I don't think this is your
problem. (we call it "aging"-- of course they are a year older after a
year whether they are used or not. ;-) )

Zai jian.

I found a strange things in my LEds device.

I made a "Batterless Bicycle Safety Lights" 12 months ago.
(http://www.freelights.co.uk).

The LEDs on the device are opened to the air, sometime raining, water
will touch the LEDs. Few days ago I found the red LEDs not working. I
checked all system, nothings is broken. Then I uses a 3v battery to
test the LEDs, the LEDs are working, but I feel the red LEDs are
little darker than the new LEDs. When I put the red LEDs back to the
device, the red LEDs still not working.

Finally, I change the red LEDs (replaced by 2 new red LEDs), the
system working again.

The problem is: Will the LEDs become older after using a while? Such
as become darker, resistence will go up.....

Someone who are know LEDs well can give me a answer. Thanks very much.

This is very important to me, because I plan to mass manufacturing
this product in low cost. If the LEDs will become older, I have to
change the designs for mass manufacturing. (To be honest, I do not
know how the do the redesign job if the LEDs do get older).

If you are interested see my redesign works for mass manufacturing, go
to:
http://www.helpyou.freewire.co.uk/redesign.html

Thanks for your help.
Chin

Best regards,
Spehro Pefhany

 

[Dave Platt]

I made a "Batterless Bicycle Safety Lights" 12 months ago.

(http://www.freelights.co.uk).

The LEDs on the device are opened to the air, sometime raining, water
will touch the LEDs. Few days ago I found the red LEDs not working. I
checked all system, nothings is broken. Then I uses a 3v battery to
test the LEDs, the LEDs are working, but I feel the red LEDs are
little darker than the new LEDs. When I put the red LEDs back to the
device, the red LEDs still not working.

Finally, I change the red LEDs (replaced by 2 new red LEDs), the
system working again.

The problem is: Will the LEDs become older after using a while? Such
as become darker, resistence will go up.....

LEDs do tend to lose some brightness over the years. This is a
significant problem for some of the "white" LEDs, which use a phosphor
layer to broaden the spectrum from a blue LED emitter... I've heard
that some of the phosphors "burn out" quite a lot after a year or so
of steady use.

Red and other monocolor LEDs don't use phosphors. They can "age" with
use, but this is normally a fairly slow process... I think they are
usually rated as having lifetime-to-50%-brightness of 100,000 hours or
so, very roughly speaking.

Now, this applies if and only if the LEDs are being used within their
ratings. LEDs do not have a fixed "resistance" - like other diodes,
they conduct very little current at voltages below their "threshold",
and then conduct very high amounts of current once the voltage exceeds
the threshold. Threshold for red LEDs is in the neighborhood of 1.2 -
1.5 volts, depending on the specific color.

LEDs are usually rated for both a maximum continuous current, and an
absolute-maximum pulse current. You can usually get away with running
an LED at current levels higher than its maximum continuous current
*if* you're feeding it pulses with a short duty cycle, but there's an
upper limit beyond which even a short pulse of high current will
either degrade or destroy the LED.

The sharpness of the current-vs.-voltage curve means that it is almost
always necessary to have _some_ form of current control or current
limiting, in order to drive an LED safely.

Also, LEDs are not very tolerant of high inverse voltages. If you
present an LED with a reverse-polarity voltage, it's likely to "break
down" (start conducting current in the reverse direction) at a
relatively low reverse voltage, and I believe I've read that this
tends to degrade the LED junction.

I looked at the "freelights" page, and I wasn't able to see whether
the little magnetic generator contains [1] any form of current
limiting, or [2] any protection against reverse voltages.

If the Freelight doesn't provide a good discharge path for the
"reverse" half of the voltage cycle generated by its little
rattling-magnet dynamo, the reverse voltage (the output of the coils)
is likely to spike up quite high, and I suspect that it'll probably
exceed the inverse-breakdown voltage of the LEDs. This is bad for 'em.

You *might* be able to fix the problems by adding a zener diode right
across the coil. Wire it so that it zeners in the forward direction
when the coil's output voltage rises up high enough that the current
through the LEDs is approaching the safety limit. The zener will also
conduct when the voltage across the coil drops below -0.7 volts (i.e.
one diode drop in the reverse direction) and this should keep the LEDs
safe from excessive inverse voltage.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Hi

I found a strange things in my LEds device.

I made a "Batterless Bicycle Safety Lights" 12 months ago.
(http://www.freelights.co.uk).

The LEDs on the device are opened to the air, sometime raining, water
will touch the LEDs. Few days ago I found the red LEDs not working. I
checked all system, nothings is broken. Then I uses a 3v battery to
test the LEDs, the LEDs are working, but I feel the red LEDs are
little darker than the new LEDs. When I put the red LEDs back to the
device, the red LEDs still not working.

Finally, I change the red LEDs (replaced by 2 new red LEDs), the
system working again.

The problem is: Will the LEDs become older after using a while? Such
as become darker, resistence will go up.....

Someone who are know LEDs well can give me a answer. Thanks very much.

This is very important to me, because I plan to mass manufacturing
this product in low cost. If the LEDs will become older, I have to
change the designs for mass manufacturing. (To be honest, I do not
know how the do the redesign job if the LEDs do get older).

If you are interested see my redesign works for mass manufacturing, go
to:
http://www.helpyou.freewire.co.uk/redesign.html

I've seen LEDs get weird, the resistance increasing, and then becoming
intermittent. But I haven't seen this happen with red LEDs. Usually
it's blue or white LEDs that have problems.

You might have a problem with sunlight overheating the LEDs when they're
outside. Or the LED maker made a bad batch of LEDs.

Also, how do you solve the brightness variation with speed?

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

On 28 Oct 2004 06:50:40 -0700, the renowned [email protected] (Q Gang)
wrote:

Chin:-

Especially some cheaper white LEDs will lose brightness after a long
time operating near maximum current, but I don't think this is your
problem. (we call it "aging"-- of course they are a year older after a
year whether they are used or not. ;-) )

I was gonna say the same thing, too. ;-)

Well, I guess it's time for a periodic update on my white LED
experiment.

I've had four white LEDs, two Nichia NSPW500BS whites, and two cheapo
Hong Kong white LEds in series on a CC power supply, running at 20 mA
since July 11. It's been about 2700 hours (for the HKs, the Nichias are
the same ones from the previous test and have another couple thousand
hours at 25 mA). The Nichias are still very bright, might have dimmed a
bit. But both HKs have dimmed very noticeably, they're putting out much
less light. They are not as dim as the pair I tested previously at 25
mA, and which dimmed very badly. The pair I'm now testing have lost, by
eyeball estimation, probably 2/3 or more of their output. No, I don't
have a light meter, this is just a simple lifetime test, with my
eyeballs, that's all.

From this and the previous test, I would say that the cheapo HK LEDs
have very poor tolerance of overcurrent, and their lifetime is severely
shortened as the current is increased beyond 20 mA. At exactly 20 mA,
their lifetime is still a lot less than the advertised 100,000 hours.
The Nichias seem to hold up well, and should be capable of sustained
high light output for more than 5 to 10 thousand hours. But the HKs
will be lucky to make it to 3000 hours (~4 months) and still have enough
light output to be considered useful. Sometime in January, at 6 months,
or about 4500 hours, I expect the cheapo HKs to be nearly useless for
even indicator grade LEDs. I'll keep everyone informed.

Zai jian.

I found a strange things in my LEds device.

[snip]

Best regards,
Spehro Pefhany

http://www.speff.com

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

[snip]

Threshold for red LEDs is in the neighborhood of 1.2 -
1.5 volts, depending on the specific color.

The threshold of IR LEDs is about 1.6 volts, but for red LEDs, it's
about 1.8 to 2.1 volts. That doesn't sound like a lot of difference,
but when you put them in series across a power source, it is very
important.


[snip]

 

[Jim Adney]

The problem is: Will the LEDs become older after using a while? Such
as become darker, resistence will go up.....

An LED run at its max current for a year will give off about half as
much light at the end of the year. I suspect that if you run them well
below their maximum current the effect will be much less.

-

 

[Ken]

An LED run at its max current for a year will give off about half as
much light at the end of the year. I suspect that if you run them
well below their maximum current the effect will be much less.

That's very true.

 

[René]

Then I uses a 3v battery to
test the LEDs, the LEDs are working, but I feel the red LEDs are
little darker than the new LEDs. When I put the red LEDs back to the
device, the red LEDs still not working.

3V - what current limiting device? With red leds the limited life span
could be a self fulfilling prophesy if exposed to a "hard" 3V?