On Fri, 21 Dec 2018 13:58:10 -0000, William Gothberg "William wrote:

On Fri, 21 Dec 2018 04:11:46 -0000, Rod Speed wrote:



"William Gothberg" "William wrote in message
news
On Fri, 21 Dec 2018 01:06:46 -0000, Rod Speed
wrote:

When a led fails, it just stops emitting light but is still electrically
identical to before it failed. This is the least likely.

I'd say it was the most likely, although from the above measurement in the
photo, it looks like they stuill conduct, but a different amount, and the
neighbour in the pair doesn't care that much.

Hard to say with the contradictory listing of the voltages.

That's confused me. If both in a pair break, they seem to conduct MORE easily, as the voltage lowers. If one breaks, it seems to conduct LESS easily, as a higher voltage is required to make the other take the same current. The only conclusion I can come to is they're failing differently depending on if they're the first or second to go in a pair. Measuring all of them - each pair obviously had the same voltage across each (I've confirmed by looking closely, they're definitely 2 LEDs in parallel, then another 2, then another 2, etc, with each pair in series with the next pair and so on, to create a string of 24 x (2 paralleled LEDs) in series.:
https://www.dropbox.com/s/1ruivl8arz...tages.jpg?dl=0
Perhaps what happens is, one fails open circuit in a pair, and the other takes slightly more voltage to conduct double the current. Eventually it wears out as it's being pushed harder, and fails in a different way, conducting.
I've also noticed that pressing lightly on the LEDs can make a broken one light up temporarily - must be something coming loose inside them.

Forgot to add, I tested shorting out a quarter of the LEDs, and the voltage at the ends drops, so it's definitely constant current.