About a couple of years ago I made up some edge lighting for a meter in a
pal's small recording studio. To replace the tiny 24v tungsten which were
forever blowing. Used 9 diffused 5mm white LEDs - 3 each in series and
one series resistor per chain of three setting the current at something
like 3 mA which was plenty bright enough - and the end result was very
even illumination. Much better than the tungsten.

Very unlikely to be the PS as that is used for other indicators too -
which were ok.

Checking things here on my own PS, it's the LEDs themselves which have all
gone low output. Some more than others - but all well down on the spares I
have from the same batch - bought off Ebay. And rather bluer than the new
spares. The series resistors are all in perfect condition - no signs of
ever even having got warm.

I've had the odd LED fail - but never anything like this. Any explanation?

--
*Starfishes have no brains *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
"Dave Plowman (News)" writes:
About a couple of years ago I made up some edge lighting for a meter in a
pal's small recording studio. To replace the tiny 24v tungsten which were
forever blowing. Used 9 diffused 5mm white LEDs - 3 each in series and
one series resistor per chain of three setting the current at something
like 3 mA which was plenty bright enough - and the end result was very
even illumination. Much better than the tungsten.

Very unlikely to be the PS as that is used for other indicators too -
which were ok.

Checking things here on my own PS, it's the LEDs themselves which have all
gone low output. Some more than others - but all well down on the spares I
have from the same batch - bought off Ebay. And rather bluer than the new
spares. The series resistors are all in perfect condition - no signs of
ever even having got warm.

I've had the odd LED fail - but never anything like this. Any explanation?

There's a large glut of LEDs on the market which have failed batch
testing - they usually end up on Ebay, but they do also turn up in
the reputable electronics supply chain, and get built into products
with a much longer design life than the LEDs actually have (often
low volume high value specialist products).

Your best bet to avoid this is to buy from reputable electronics
supply chain, but that's still no guarantee.

It sounds like the ones you bought were produced extremely cheaply;
poor quality LEDs and too little phosphor. At a couple of years old,
they can't have done even 20000 hours, even if used 24/7.
What is their forward current rating?
What is their operating temperature likely to be?

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Tue, 20 Dec 2016 11:06:29 +0000 (GMT), "Dave Plowman (News)"
wrote:

And rather bluer than the new
spares.


Which would suggest the fluorescent material has deteriorated and UV
is escaping??

AJH

On Tuesday, 20 December 2016 11:06:39 UTC, Dave Plowman (News) wrote:
About a couple of years ago I made up some edge lighting for a meter in a
pal's small recording studio. To replace the tiny 24v tungsten which were
forever blowing. Used 9 diffused 5mm white LEDs - 3 each in series and
one series resistor per chain of three setting the current at something
like 3 mA which was plenty bright enough - and the end result was very
even illumination. Much better than the tungsten.

Very unlikely to be the PS as that is used for other indicators too -
which were ok.

Checking things here on my own PS, it's the LEDs themselves which have all
gone low output. Some more than others - but all well down on the spares I
have from the same batch - bought off Ebay. And rather bluer than the new
spares. The series resistors are all in perfect condition - no signs of
ever even having got warm.

I've had the odd LED fail - but never anything like this. Any explanation?

**** LED's via ebay, can't quite imagine LEDs running at 3ma I have some low current ones that aren't very bright they run at 2ma.

"Dave Plowman (News)" wrote:
About a couple of years ago I made up some edge lighting for a meter in a
pal's small recording studio. To replace the tiny 24v tungsten which were
forever blowing. Used 9 diffused 5mm white LEDs - 3 each in series and
one series resistor per chain of three setting the current at something
like 3 mA which was plenty bright enough - and the end result was very
even illumination. Much better than the tungsten.

Very unlikely to be the PS as that is used for other indicators too -
which were ok.

Checking things here on my own PS, it's the LEDs themselves which have all
gone low output. Some more than others - but all well down on the spares I
have from the same batch - bought off Ebay. And rather bluer than the new
spares. The series resistors are all in perfect condition - no signs of
ever even having got warm.

I've had the odd LED fail - but never anything like this. Any explanation?

We had two GU10 LEDs that did the same, very much reduced output after
a year or so of use. All the electronics is inside the 'bulb' but I
still don't really understand how they managed to go so much dimmer
without actually failing.


--
Chris Green
·

On 20/12/2016 11:06, Dave Plowman (News) wrote:
About a couple of years ago I made up some edge lighting for a meter in a
pal's small recording studio. To replace the tiny 24v tungsten which were
forever blowing. Used 9 diffused 5mm white LEDs - 3 each in series and
one series resistor per chain of three setting the current at something
like 3 mA which was plenty bright enough - and the end result was very
even illumination. Much better than the tungsten.

Very unlikely to be the PS as that is used for other indicators too -
which were ok.

Checking things here on my own PS, it's the LEDs themselves which have all
gone low output. Some more than others - but all well down on the spares I
have from the same batch - bought off Ebay. And rather bluer than the new
spares. The series resistors are all in perfect condition - no signs of
ever even having got warm.

Sounds like the phosphor isn't stable so that they are now leaking more
blue light. Never seen a problem like that with any LEDs I have bought
but I am careful not to buy them from untrusted sources on eBay.

If you were running them continuously at 30mA and Tj around 120C then I
could believe that they might struggle after a couple of years but run
cool at 3mA I can't see how they should fail apart from an intrinsic
manufacturing defect. The odd one may fail taking out a chain but what
you are describing sounds like a low quality unstable phosphor.

LED indicators I installed in the mid 70's when they were expensive and
new are still going strong after all this time and ~5mA.

Even the ones for low power lighting I have running at 750mA on
heatsinks have been fine for years of extended use.

I've had the odd LED fail - but never anything like this. Any explanation?

Dodgy batch of unknown provenance. Dodgy capacitors are *much* worse.

--
Regards,
Martin Brown

On Tuesday, December 20, 2016 at 11:06:39 AM UTC, Dave Plowman (News) wrote:
About a couple of years ago I made up some edge lighting for a meter in a
pal's small recording studio. To replace the tiny 24v tungsten which were
forever blowing. Used 9 diffused 5mm white LEDs - 3 each in series and
one series resistor per chain of three setting the current at something
like 3 mA which was plenty bright enough - and the end result was very
even illumination. Much better than the tungsten.

Very unlikely to be the PS as that is used for other indicators too -
which were ok.

Checking things here on my own PS, it's the LEDs themselves which have all
gone low output.

partial film failure on the actual die is also an explanation have heard.

Possibly made from contaminated wafers way back in the chain, probably dropped through a few QC sieves before reaching ebay.

One possible weeding test is very low current performance, uA , duffers wont fire up until get a big enough kick, posh leds will light with virtually nothing.



Some more than others - but all well down on the spares I
have from the same batch - bought off Ebay. And rather bluer than the new
spares. The series resistors are all in perfect condition - no signs of
ever even having got warm.

If they didn`t spend the dosh on the dice , premium phosphors would have been a no as well.

Power density within an LED is very high.


I've had the odd LED fail - but never anything like this. Any explanation?

Nichia can still command 60p an LED for a reason, best dice , best phosphors , tight binning and reliability have a cost.

https://www.rapidonline.com/nspw500d...000mcd-50-0700

--
*Starfishes have no brains *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
says...

Checking things here on my own PS, it's the LEDs
themselves which have all gone low output...

...And rather bluer than the spares.

I've had the odd LED fail - but never anything like
this. Any explanation?

My understanding is that White LEDs are actually blue LEDs
which also produce UV which causes a yellow phosphor to
fluoresce. The 'white' light is a combination of the two.

So, perhaps in your case it is the phosphor which is under
performing, thus the blue shift.

--

Terry

Terry Casey wrote:

My understanding is that White LEDs are actually blue LEDs
which also produce UV which causes a yellow phosphor to
fluoresce. The 'white' light is a combination of the two.

AIUI older "white" ones can be UV LED with phosphors to turn the UV into
R+G+B, or newer ones are blue LED with phosphors to turn (some of the)
blue into R+G.

In article ,
Andrew Gabriel wrote:
In article ,
"Dave Plowman (News)" writes:
About a couple of years ago I made up some edge lighting for a meter
in a pal's small recording studio. To replace the tiny 24v tungsten
which were forever blowing. Used 9 diffused 5mm white LEDs - 3 each
in series and one series resistor per chain of three setting the
current at something like 3 mA which was plenty bright enough - and
the end result was very even illumination. Much better than the
tungsten.

Very unlikely to be the PS as that is used for other indicators too -
which were ok.

Checking things here on my own PS, it's the LEDs themselves which have
all gone low output. Some more than others - but all well down on the
spares I have from the same batch - bought off Ebay. And rather bluer
than the new spares. The series resistors are all in perfect condition
- no signs of ever even having got warm.

I've had the odd LED fail - but never anything like this. Any
explanation?

There's a large glut of LEDs on the market which have failed batch
testing - they usually end up on Ebay, but they do also turn up in
the reputable electronics supply chain, and get built into products
with a much longer design life than the LEDs actually have (often
low volume high value specialist products).

They were certainly inexpensive. But I've bought lots from Ebay direct
from China or whatever that seem to have lasted OK.

Your best bet to avoid this is to buy from reputable electronics
supply chain, but that's still no guarantee.

Oh dear. ;-)

It sounds like the ones you bought were produced extremely cheaply;
poor quality LEDs and too little phosphor. At a couple of years old,
they can't have done even 20000 hours, even if used 24/7.

I did ask, and the studio is powered down when not in use. So I doubt rums
for much more than 50 hours a week on average.

What is their forward current rating?

Can't find the details but remember it as being a normal 20mA or so - and
that they are run well below that as they were too bright. My brief was to
give very even illumination hence using 9 of them on a 95mm wide meter.

What is their operating temperature likely to be?

Being an additional meter - a stereo PPM - mounted in a pod, room
temperature plus their own heat. I doubt a moving coil meter generates
much heat even when hammering the end stops. ;-)

--
*If you try to fail, and succeed, which have you done?

Dave Plowman London SW
To e-mail, change noise into sound.

On 20/12/2016 12:50, Andy Burns wrote:
Terry Casey wrote:

My understanding is that White LEDs are actually blue LEDs
which also produce UV which causes a yellow phosphor to
fluoresce. The 'white' light is a combination of the two.

AIUI older "white" ones can be UV LED with phosphors to turn the UV into
R+G+B, or newer ones are blue LED with phosphors to turn (some of the)
blue into R+G.

Not really. The breakthrough for making white LEDs was getting a high
efficiency blue emitter that was short wavelength enough to excite the
yellow phosphor. UV leds have always had (much) worse efficiencies and
have had to jump through more hoops to get to manufacture.

http://www.ledsmagazine.com/articles...-lawsuits.html

AFAIK there was never a time when UV LEDs were used for white. They were
too exotic, expensive and inefficient compared to shortwave blue.

--
Regards,
Martin Brown

In article ,
Andy Burns writes:
Terry Casey wrote:

My understanding is that White LEDs are actually blue LEDs
which also produce UV which causes a yellow phosphor to
fluoresce. The 'white' light is a combination of the two.

AIUI older "white" ones can be UV LED with phosphors to turn the UV into
R+G+B, or newer ones are blue LED with phosphors to turn (some of the)
blue into R+G.

They're mostly blue LEDs with phosphors to turn (some of the)
blue into R+G. There's no UV from these.

There are UV ones - they are used where more control of the
colour is required, and/or the light source for the R+G needs
to be in exactly same place as the blue so they don't focus
in different places. They're significantly more expensive to
make (and possibly less efficient due to increased Stokes
shift, although I haven't actually compared them).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Well it was many years ago, when I bought some super bright red leds for
power indicators on some home built devices. After about a year or so, they
had dimmed. Its of course hard to say exactly what had happened but it
seemed to me that although LEDs do run quite cool you can still feel heat on
their bodies when in use, so maybe there is either a chemical change in the
material, or the interface with the body material that changes over time due
to either cycling or just prolonged heating.

Of course whit LEDs are more complex, being more than one colour in the
package, and I'd not be surprised if one colour goes lower emission than
others as it ages.
I suppose we are still in relative early days with this form of lighting as
light sources not just indicators still.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Dave Plowman (News)" wrote in message
...
About a couple of years ago I made up some edge lighting for a meter in a
pal's small recording studio. To replace the tiny 24v tungsten which were
forever blowing. Used 9 diffused 5mm white LEDs - 3 each in series and
one series resistor per chain of three setting the current at something
like 3 mA which was plenty bright enough - and the end result was very
even illumination. Much better than the tungsten.

Very unlikely to be the PS as that is used for other indicators too -
which were ok.

Checking things here on my own PS, it's the LEDs themselves which have all
gone low output. Some more than others - but all well down on the spares I
have from the same batch - bought off Ebay. And rather bluer than the new
spares. The series resistors are all in perfect condition - no signs of
ever even having got warm.

I've had the odd LED fail - but never anything like this. Any explanation?

--
*Starfishes have no brains *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Brian Gaff wrote:
Well it was many years ago, when I bought some super bright red leds for
power indicators on some home built devices. After about a year or so,
they had dimmed. Its of course hard to say exactly what had happened
but it seemed to me that although LEDs do run quite cool you can still
feel heat on their bodies when in use, so maybe there is either a
chemical change in the material, or the interface with the body
material that changes over time due to either cycling or just prolonged
heating.

I have seen some pretty old indicator LEDs that are no longer in the first
flush of youth. But then they were usually driven fairly hard. This is the
first similar I've seen that gave problems after such a short time -
especially since they were gently driven.

--
*I have my own little world - but it's OK...they know me here*

Dave Plowman London SW
To e-mail, change noise into sound.

On Tue, 20 Dec 2016 03:54:48 -0800 (PST), whisky-dave wrote:

**** LED's via ebay, can't quite imagine LEDs running at 3ma I have
some low current ones that aren't very bright they run at 2ma.

Have a cheapo NAS with a blue LED indicator on the front. A night it
would be dazzleling and light up the entire room. I "got at it" and
inserted a series resistor to drop the brightness. In the process I
found it would glow with the leakage current through dry fingers
lightly holding the wire. Eventually settled on 50 uA (micro amps)
and it was still on the bright side.

Been playing with fairy lights and a Raspbery Pi as you do at this
time of year. Raided from a commercial battery operated 240 LED set
I've got 6 chains of 40 parallel connected bright white LEDs, each
chain takes no more than 20 mA flat out = 0.5 mA/LED. The Pi provides
programable, independant PWM control of each chain.

--
Cheers
Dave.

Dave Plowman (News) has brought this to us :
To replace the tiny 24v tungsten which were
forever blowing.

Tungsten is happy on AC, LED's are not. Any chance the 24v might be AC,
or have an AC component?

In article l.net,
Dave Liquorice wrote:
**** LED's via ebay, can't quite imagine LEDs running at 3ma I have
some low current ones that aren't very bright they run at 2ma.

Have a cheapo NAS with a blue LED indicator on the front. A night it
would be dazzleling and light up the entire room. I "got at it" and
inserted a series resistor to drop the brightness. In the process I
found it would glow with the leakage current through dry fingers
lightly holding the wire. Eventually settled on 50 uA (micro amps)
and it was still on the bright side.

Yup. I changed the old red 5mm LED in my Quad 405 to a modern blue one,
and was amazed how low I had to set the current to make it acceptable.

--
*Work is for people who don't know how to fish.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Harry Bloomfield wrote:
Dave Plowman (News) has brought this to us :
To replace the tiny 24v tungsten which were
forever blowing.

Tungsten is happy on AC, LED's are not. Any chance the 24v might be AC,
or have an AC component?

No. It's a fairly standard PS for that sort of thing - used to drive
relays too. Definitely DC. And well smoothed.

--
*Cover me. I'm changing lanes.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
"Dave Plowman (News)" writes:
In article l.net,
Dave Liquorice wrote:
**** LED's via ebay, can't quite imagine LEDs running at 3ma I have
some low current ones that aren't very bright they run at 2ma.

Have a cheapo NAS with a blue LED indicator on the front. A night it
would be dazzleling and light up the entire room. I "got at it" and
inserted a series resistor to drop the brightness. In the process I
found it would glow with the leakage current through dry fingers
lightly holding the wire. Eventually settled on 50 uA (micro amps)
and it was still on the bright side.

Yup. I changed the old red 5mm LED in my Quad 405 to a modern blue one,
and was amazed how low I had to set the current to make it acceptable.

Yes, I have a row of 6 diagnostic LEDs on my Raspberry Pi heating
controller using a few different colours. There's one blue one
(indicates boiler burner on, i.e. flame colour), and ISTR I ended
up with 1/20th of the current through that one compared with the
othees, and it's still much brighter.

It wouldn't surprise me if it was more efficient to make a red LED
using one of the blue ones, a red phosphor, and a blue blocking filter,
inspite of the Stokes shift and other losses.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andrew Gabriel wrote:

It wouldn't surprise me if it was more efficient to make a red LED
using one of the blue ones, a red phosphor, and a blue blocking filter,
inspite of the Stokes shift and other losses.

I think that must be done with some of the "clear straw hat" LEDs.

I have a multi-coloured R/G/B/Y set from ADSA, designed to run from 2xAA
with no limiting resistors anywhere (unless buried within the LEDs
themselves) so all colours run at the same ~3V, in fact I run them at 4V
from a PSU, they've lasted 2 years of christmas without any burning out
so far.

In article ,
Andrew Gabriel wrote:
Your best bet to avoid this is to buy from reputable electronics
supply chain, but that's still no guarantee.

It sounds like the ones you bought were produced extremely cheaply;
poor quality LEDs and too little phosphor. At a couple of years old,
they can't have done even 20000 hours, even if used 24/7.

Because of the time of year and possibly slower postage, I've just
replaced them with the identical spares I had. Which will at least sort it
for some time.

But will get some better spares for next time. Any suggestions for the
most reliable supplier? The spec would be 5mm diffused warm white. They
don't need to be super efficient or whatever, as power isn't a problem.

--
*A backward poet writes inverse.*

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
"Dave Plowman (News)" writes:
In article ,
Andrew Gabriel wrote:
Your best bet to avoid this is to buy from reputable electronics
supply chain, but that's still no guarantee.

It sounds like the ones you bought were produced extremely cheaply;
poor quality LEDs and too little phosphor. At a couple of years old,
they can't have done even 20000 hours, even if used 24/7.

Because of the time of year and possibly slower postage, I've just
replaced them with the identical spares I had. Which will at least sort it
for some time.

But will get some better spares for next time. Any suggestions for the
most reliable supplier? The spec would be 5mm diffused warm white. They

I have bought those from Rapid in the very distant past (2700K).
Can't recall if they were diffuse or not though. (I have attacked
5mm/3mm LEDs with sandpaper on occasion.)

don't need to be super efficient or whatever, as power isn't a problem.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 24/12/2016 10:54, Dave Plowman (News) wrote:
In article ,
Andrew Gabriel wrote:
Your best bet to avoid this is to buy from reputable electronics
supply chain, but that's still no guarantee.

It sounds like the ones you bought were produced extremely cheaply;
poor quality LEDs and too little phosphor. At a couple of years old,
they can't have done even 20000 hours, even if used 24/7.

Because of the time of year and possibly slower postage, I've just
replaced them with the identical spares I had. Which will at least sort it
for some time.

But will get some better spares for next time. Any suggestions for the
most reliable supplier? The spec would be 5mm diffused warm white. They
don't need to be super efficient or whatever, as power isn't a problem.

AT the risk of degrading their longevity due to vibration and if you are
intending to use them for what I think then you can make a cylindrical
lens by very carefully drilling though the clear plastic of the water
clear type to make a spread beam in one dimension.

Expect to trash a few before you get it right. I don't know why makers
dont package some in a water clear cylindrical negative lens for diffuse
area illumination for side lighting older meter displays.

--
Regards,
Martin Brown