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Re: Dead LEDs
by Bob Axtell-3
::
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Russell,
The problem with the white LEDS is similar to problems with other Chinese
goods (i.e.
Li-Ion cells, many other items). The causes seems to be poorly-made
chemicals. The
raw chemicals used in many processes don't seem to be chemically pure enough
for
the task at hand. The labor is fine, the business practices are OK (but not
to Western standards), but critical chemicals don't seem to be available.
That's why a battery maker is able to make decent batteries for months then
make a batch of really shoddy goods one
week. That's what I was told when _I_ asked about it...
--Bob
On Wed, Jul 16, 2008 at 6:33 AM, Apptech <apptech@...> wrote:
> Getting White LEDs with long lifetimes is easy. Getting them
> at a low cost is another matter.
>
> I've been testing various white LEDs for longevity and been
> getting some rather bad results from Chinese sourced
> products. Reports from others testing LEDs for the same
> purpose are similar. This is not a total surprise as the
> general received wisdom is that this is the case. It is
> however a somewhat surprise as it is not obvious why the
> Chinese products should tend to be so bad. A Chinese
> supplier (name will not be stated) even made some changes to
> try and meet my spec and the results were no better.
>
> By Chinese I mean companies that are Chinese based - NOT
> known internationals who are domiciled elsewhere but may use
> Chinese manufacturing (eg Avago, Cree, Nichia, ...) - such
> companies are demonstrably more liable to get it right.
>
> The universal claim is that white LEDs last 100,000 hours. I
> can assure you that many don't come anywhere close (by 2+
> orders of magnitude in some cases).
>
> My questions are:
>
> - What mechanism makes Chinese LEDs so bad?
>
> - Why is this allowed to be? ie why don't they do whatever
> it takes to fix it.
>
> If anyone feels that my statements are a generalisation and
> that some Chinese white LEDs do have the sort of lifetimes
> one would expect then *PLEASE* do tell me the brands!. I'd
> be extremely happy to be wrong and to be able to source LEDs
> at non-market-leader prices.
>
> For white phosphor LEDs (blue radiator and yellow phosphor
> re-radiator) the degradation mechanism seems to be actual
> LED die output level. A possible mechanism in some cases MAY
> be die over-temperature due to excessive over-rating of die
> current capabilities. Phosphor death does not seem to be an
> issue in what I have seen. (it is in some other cases). Die
> bonding adhesive to the LED structure cup is claimed to be a
> problem in some cases but when this was changed in the LEDs
> I was getting to a Japanese sourced bonding product of good
> parentage it made about zero difference.
>
> Interestingly, and not directly related, some name brand
> LEDs give atrocious spectral results at very low currents
> while others are about as good across a wide range of
> currents.
>
>
>
> Russell
>
>
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>--
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
The problem with the white LEDS is similar to problems with other Chinese
goods (i.e.
Li-Ion cells, many other items). The causes seems to be poorly-made
chemicals. The
raw chemicals used in many processes don't seem to be chemically pure enough
for
the task at hand. The labor is fine, the business practices are OK (but not
to Western standards), but critical chemicals don't seem to be available.
That's why a battery maker is able to make decent batteries for months then
make a batch of really shoddy goods one
week. That's what I was told when _I_ asked about it...
--Bob
On Wed, Jul 16, 2008 at 6:33 AM, Apptech <apptech@...> wrote:
> Getting White LEDs with long lifetimes is easy. Getting them
> at a low cost is another matter.
>
> I've been testing various white LEDs for longevity and been
> getting some rather bad results from Chinese sourced
> products. Reports from others testing LEDs for the same
> purpose are similar. This is not a total surprise as the
> general received wisdom is that this is the case. It is
> however a somewhat surprise as it is not obvious why the
> Chinese products should tend to be so bad. A Chinese
> supplier (name will not be stated) even made some changes to
> try and meet my spec and the results were no better.
>
> By Chinese I mean companies that are Chinese based - NOT
> known internationals who are domiciled elsewhere but may use
> Chinese manufacturing (eg Avago, Cree, Nichia, ...) - such
> companies are demonstrably more liable to get it right.
>
> The universal claim is that white LEDs last 100,000 hours. I
> can assure you that many don't come anywhere close (by 2+
> orders of magnitude in some cases).
>
> My questions are:
>
> - What mechanism makes Chinese LEDs so bad?
>
> - Why is this allowed to be? ie why don't they do whatever
> it takes to fix it.
>
> If anyone feels that my statements are a generalisation and
> that some Chinese white LEDs do have the sort of lifetimes
> one would expect then *PLEASE* do tell me the brands!. I'd
> be extremely happy to be wrong and to be able to source LEDs
> at non-market-leader prices.
>
> For white phosphor LEDs (blue radiator and yellow phosphor
> re-radiator) the degradation mechanism seems to be actual
> LED die output level. A possible mechanism in some cases MAY
> be die over-temperature due to excessive over-rating of die
> current capabilities. Phosphor death does not seem to be an
> issue in what I have seen. (it is in some other cases). Die
> bonding adhesive to the LED structure cup is claimed to be a
> problem in some cases but when this was changed in the LEDs
> I was getting to a Japanese sourced bonding product of good
> parentage it made about zero difference.
>
> Interestingly, and not directly related, some name brand
> LEDs give atrocious spectral results at very low currents
> while others are about as good across a wide range of
> currents.
>
>
>
> Russell
>
>
>
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
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