Is there a way to non destructively measure the junction temperature, since lumen output falls the hotter the internals of the led gets, it may be interesting to find out how hot they get as we use them.
I’ve seen very thin thermistors before. you can thermal glue very close to die. Otherwise you need an expensive thermal camera. One idea would be to emulate one with Ir filter in front of digital camera/webcam without strong IR filtering itself (calibrate w/ boiling/frozen water).
That won’t work… standard CCD sensors does not see far enough into the IR to detect the die temperature. My best 3rd gen night vision goggles see much deeper into the IR, and can barely see something at 150C
You can measure temperature with forward voltage. But these is long procedure and you need fast DMM with memory or osciloscope.
I don’t think there’s a way to non destructively do it… The only way I can think of is to try to turn it on without the head, and point maybe an infrared thermometer at the junction.
But you can do it only with right equipment, and it takes several hours for just one LED.