UPDATE LED Life Test at 2 Months

Watson A.Name - "Watt Sun, th · 2004-07-06T01:10:34+00:00

I I've had the 4 LEDs operating at 25 mA for all of May and June, andthe first few days of July. This is about 1500 hours so far. The LEDsare two Nichia NSPW500BS white LEDs, and two white LEDs from Hong Kongthat I got off Ebay. All four are in series so there is no doubt thatthey are all running at exactly the same current.The two Nichias are going strong, with no noticeable signs of dimming.The two Hong Kong LEDs, sad to say, are so dim that they wouldn't makegood panel lights, so can't even consider them suitable forillumination. They're really quite dim.Of the hundred Hong Kong LEDs I bought, all I've used have had thisdimming problem after a few hundredds of hours, so I decided to put thefour on a PS to control the conditions and verify that I'm not imaginingthings. I think one problem might be that the Hong Kong LEDs use anorganic phosphor that degrades faster than Nichia's, and mightcontaminate the LED chip. But I'm not an expert on this at all, so I'mopen to any other ideas.I posted an update of the progress of the dimming at the beginning oflast month, and now this one shows that the hong kong LEDs are so dimthat it's probably not worth continuing the test. I may solder two moreunused hong kong LEDs into the circuit, and start the test again, justfor the halibut.--@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@###Got a Question about ELECTRONICS? Check HERE First:### email address is whitelisted. *All* email sent to itgoes directly to the trash unless you add NOSPAM in theSubject: line with other stuff. alondra101 Don't be ripped off by the big book dealers. Go to the URLthat will give you a choice and save you money(up to half). You'll be glad you did!Just when you thought you had all this figured out, the gov'tchanged it:

Jul 06, 2004 22 Replies

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Mike Harrison 22 years ago

..and what do they mean by 'last'... it may still produce _some_ output after that time, but how much?

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Tim Shoppa 22 years ago

"Can last 100,000" hours is awfully vague. Is that a lifetime or a MTBF? (The two are not the same... the MTBF of a US Soldier in Vietnam was

280 years, for example.) Under what conditions?

Agilent and Nichia have some really good documents on their websites about how they test their LED's. They probably don't apply to E-bay sellers :-).

Tim.

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Mark Mcmillan 22 years ago

I remember being told once in the case of normal LEDs (no phosphor) that over time (powered) and power cycling and at higher currents that, micro fractures occur in the die and as these accumulate they prevent the light from escaping from the die hence less light output. True or not I do not know.

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