Re: Dead LEDs

> 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
>
>
>
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