Running LEDS VERY hot

I am new here, so hope I am not running over an old topic.

Since the problem with heat is thermal runaway, has anyone
used a current limiter and run an LED very hot (like ~ 100C)
I would imagine that so long as one kept strict limits on
current, that heat would not be such a big issue.

Well...

LEDs tend to get less efficient and age faster when they are hotter, so it is often good design practise to keep them cool.

On the other hand, the maximum junction temperature is rated at about 125°C (depends on the device) so it is entirely possible to run LEDs at rather high temperatures if other design constraints require it.

-Jon

Look around and you'll find that many people have run Luxeons in "severe overdrive" conditions, either resistored or with high-current BadBoys.

I believe some people have used BadBoy 750s with 1W Luxeons, although most 750s are used to drive 5Ws at slightly above spec instead of 1Ws at over 2x spec current.

IIRC, LumiLeds has announced that the 1W is good up to 1A as long as the thermal conditions are met (ie GOOD heatsink).

As long as you stay below the 125 deg junction temp, it should work. But how do you get the LED hot with a current limit? You can fry them with a too high voltage, also. I have overdriven single LED's (white, rated @ 30ma) up to 100ma. Failures (apparently from thermal runaway) start occuring at 80ma & higher. Some did not fail, but were in the process, judging by the rapidly reducing light output & heat increase. I don't know what the max forward voltage is for these, but there is one. Above that your semiconductor becomes a conducter (shorts), until it burns up (melts?).
Using even a small resistor seems to prevent thermal runaway (within limits, I haven't done that much testing. For example, I have a 3 AA flashlight direct driving 4 LEDs using 3 lithium 1.5v AA batteries and a 10 ohm resistor (I don't recall the current, over 120ma IIRC). I'll test again with fresh batteries & let y'all know............RussH

My very point, strict current limiting avoids runaway
(it is the current that runs away)
Controlling the voltage will not hack it.