On 05/06/2018 15:44, Dave Plowman (News) wrote:
In article ,
Harry Bloomfield wrote:
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 would have expected it to produce the same light output then deteriorate
rapidly as the batteries reach the end of their life.

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).

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.

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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Regards,
Martin Brown