Yes, that is some incredible fact, they are still working on 80-100% forward current but they light darker or generally go out on 1-15% nominal forward current.
In fact i'am looking for what is damaged, pn junction, micro resistance of wire bond, anode or cathode, damaged structure of cristal structure of pn junction. The manufacturer guarantee is one case, but the second, is abnormal LED chips work - I ve never seen before and any other engineer... So thats why we are trying
establish fact and reason.
The diode manufacturer said, the test in their laboratory will cost over 40 000 USD.
Of course, i sad that diodes works fine at 80-100 forward current but... The humans eye cant deceive us, and it is very possible that we can't register abnormal damaged LED work.
I will try to send luminaries to laboratory with goniophotometer to measure total flux, and will try to measure forward voltage of one diode. But it is very interesting, and looks like the damaged diodes have changed gap bands width of pn junction, so that's why phenomenon of electroluminescence is so weak with lower forward current. Maybe the material has changed their own special properties , and pn junction has much bigger resistance. This fact could explain why diode work, not flickering but glowing is darker than healthy diode - the LED diode resistance is not linear like resistors, has a greater dynamics of change like below:
Currently (i think) the characteristics has changed and resistance changing like voltage at lower current value - the changes are characterized by step change. It is linked with changed gap band what could have influence for characteristics and for example some part of electrons recombination is changed to auger effect, so we lost energy, diode emitting more heat, and much less photons.
So maybe it is simple way to check smd diodes - power the health and damaged diode with the same current 1/10 (nominal) and measure voltage drops, heat and flux. Of course the result wouldn't give an answer what was destroyed but give me some evidence, is it good or bad experiment direction.
** I don't know what is the energy of auger electron compared to photons in the same material, semiconductor type.