Cree led deterioration

I was going to ask last week if Cree LED's deteriorated with age, but I have just installed a new set of batteries (3x AAA) and it is back to its full amazing power. I bought the little Cree torch around 8 years ago in Aldi or Lidl and I was astounded by its intensity of its beam. I guess I rather expected it to just rapidly dim as the batteries failed, rather than the slow deterioration I got. A battery tester suggested the batteries were still good.
I also had in mind to keep my eyes open for another Cree torch as a replacement.
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It should be borne in mind there is 'Cree' and 'ebay Cree', the latter being whatever LEDs the Chinese vendor managed to find and label as Cree. I wouldn't be surprised if the latter isn't as high quality. I'd expect Aldidl quality to be somewhat better.
Theo
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I would have expected it to produce the same light output then deteriorate rapidly as the batteries reach the end of their life.
Only LEDs I've had which deteriorated - rather than fail - were some cheap warm white low current types. They got dimmer and dimmer - despite being conservatively driven.
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On 05/06/2018 15:44, Dave Plowman (News) wrote:

For short bursts quite badly deteriorated batteries can drive an LED torch OK - especially one which has a voltage to current converter drive for the LED. It will run the batteries down until they leak if you let it (especially one with three batteries where the weakest one dies).

That is quite unusual. The only power LEDs I have ever seen dim with age have been on inadequate heatsinking and run *very* hard. After a while you can see blackening of the previously yellow phosphor and yellowing of the nominally water clear plastic lens.
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These looked perfectly normal. They were used to illuminate a meter - replacing the original pea bulbs.
I just assume I got a bad batch somehow. They were pretty cheap ones from China via Ebay. Not silly cheap though. Replaced them using exactly the same drive electronics, and those have been fine.
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On 06/06/2018 17:26, Martin Brown wrote:

+1, IME even cheap eBay "Crees" last very well. I have them all over the place.
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I think it very much depends on the circuit running the leds. Some of them actually use a stabilisation system so the battery really needs to be pretty knackered for it to dim, while others perform more like a real old fashioned torch and the light dims as the battery volts drop.
Brian
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On 06/06/2018 07:25, Brian Gaff wrote:

If the torch has three cells I suspect it's connected directly to the LEDs with resistors to drop the voltage to 4V and limit the current. A torch with two cells must have some kind of voltage multiplier which may regulate the current in a clever way as the battery drains.
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Yes - have a two D cell Lidl one which is brilliant. That seems to stop working suddenly. But has a very good battery life.
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Dave Plowman (News) wrote :

All are a long way from the glow worm filament lamps of a few years ago.
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Absolutely. If only domestic LEDs gave the same improvment over tungsten (I'm not talking efficiency)
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On Wed, 06 Jun 2018 07:25:00 +0100, Brian Gaff wrote:

Avoid the ones that utilise 3 or 4 AA cells since that *usually* indicates the use of a simple dropper resistor to limit the LED current to a safe maximum limit on a fresh battery of cells. Not only is this wasteful of expensive battery energy, it also leads to a rapid reduction in light output and a shortening of battery life during the all too brief useful light output phase.
A much safer bet that a proper electronic ballast circuit has been used to stabilise the light output efficiently and improve battery life, is to pick a torch that uses only one or two cells since the lower voltage mandates the use of an electronic ballast to drive the LED.
That's not to say a 3 or 4 cell torch can't use a proper electronic ballast module as in the case of the LED bulb upgrade modules for the three D cell "Maglight" torches and clones, it just seems so unlikely that anyone would encumber a 'designed from scratch' electronically ballasted LED torch with more cells than are strictly required.
In the days before LED Torch bulbs existed, there was a very good reason to use 3 or 4 D cells in a torch; the higher wattage tungsten filament torch bulbs needed that extra voltage (and battery life) to provide the brighter light output for which they'd been designed.
The only downside of an electronically ballasted LED torch is the ballast circuit's negative load impedance which makes battery contact resistance effects even more of a nuisance than they were with good old fashioned torch bulbs (and the tungsten filament torch bulbs had their own built in negative impedance effect due to their extremely positive temperature coefficient of resistance over their normal working voltage range). Good quality high pressure spring battery contacts are a vital part of a modern day torch using an electronically ballasted LED lamp.
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Johnny B Good presented the following explanation :

Thanks, I was thinking to buy a newer one anyway.
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