Re: Dead LEDs

> Mind you to ellaborate a bit on how you test LEDs for longevity?
>
> How do you accelerate the process to understand 100K hours is wrong or
> what
> variables/instrument do you use to measure performance?
>
> 2008/7/16 Apptech <apptech@...>:
>
>> 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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>
>
>
> --
> Ariel Rocholl
> Madrid, Spain
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