Seconds. It’s like 10 seconds, less with fragile E21A
EDIT: My rule is to never get past 1,5x rated max current.
[Clemence]
Okay, but you later said,
That seems to say 500 hours when driven at 5A (1.66x rated max current). Or are you saying that the full 5% damage gets done in the first 10 seconds, then almost nothing after that?
Are we talking about the same LEDs? I thought this was about Cree LEDs, like the XML or XPL. What current are you using to do significant damage in 10 seconds? It’s got to be way more than 5A. If you’re trying to shove 8 or 9 amps into the LED, then I can totally believe 10 seconds. But if it’s 5 amps, I don’t think Cree’s LM80 stats or personal usage of high-output lights backs that up.
Yeah, let’s be careful about what the datasheets says.
The LEDs are probably tested on non DTP MCPCBs, or high performance aluminium MCPCBs.
The type of MCPCBs we use transfer heat much more effectively to the body, meaning the LED is probably running much cooler under load vs on an aluminium MCPCB.
And most of our lights can’t overdrive LEDs for very long because of thermal control.
That 500 hours was my guesstimation derived from Cree’s LM80 data. But Cree never published anything above 3A - their max rated current.
I tested below LEDs:
- Nichia: 219C, 319A, E21A, 144AM/AR, 757GRV3, E17A
- Cree: XPL, XPL-HI, XPG, XTE, XPG2, XPE2, XHP50, (sorry, no XML or XML2)
- Some Citizen COB
- Some unknown LED bulb LEDs
Cree is tougher than other LED I tested, but still suffer invisible damage (output reduction) at above 1,5 - 2x rated current. Whenever I get past max rated current, whenever I redo the output test, the voltage always reduced. The farther away from max rated current, the lower the voltage became. Lower forward voltage is a clear sign that output has permanently reduced. My test requires me to keep the LED at certain current for almost 2 minutes in each increment. I only write down the output after the voltage has stabilized. LED Vf is a very accurate good thermal sensor.
But as I said earlier, I sometimes forgot or skipped something and made me step backwards. Whenever I did this above max rated current, the voltage always permanently reduced. Even if I just stayed at the higher current step for few seconds
[Clemence]
I have never done specific tests for this, so what I know is some peculiarities that many leds showed that I tested.
1) after a led test (that usually goes well beyond specifications), in cases that they did not seem to have damaged the led, I often go back to a reasonable current within specs and let the led stabilise at that current. The output is always a bit (often just 1 or 2%, nothing serious usually) lower than the initial output at that current, and the voltage has dropped a bit. If I increase the current a bit to get back to the voltage that I originally measured, the output is exactly what I originally measured with non-increased current (so after overdriving the output seems to “follow” the voltage rather than the current). Of course now the output per Watt has suffered a bit.
2) there seems to be a recovery of the led over a longer period than a few minutes. Not just with bare leds but also with output/throw measurements of flashlights, I noticed several times that a re-measurement after a couple of minutes always gives a lower result, even when the light was fully cooled down, but when waited a day the measurement was back up again at the first value.
But as I said, this is all circumstantial observations that I gathered over time without specific testing for it, Clemence has already done more proper testing on this than I.
You can do some real quantitative testing specificially looking for the effects and get much more information, about how partial this recovery is for instance.
Has anyone ever done a long term lumen maintenance test on an LED? Something like running an XP-L HI at 5A (typical DD current) for a few hours or days to see how it holds up.
Interesting stuff. 1% or 2% doesn’t sound too bad, if you were driving things really hard to test failure currents. Strange about the long-term recovery of the LED, though. I would have thought if it didn’t recover within a few minutes, it wouldn’t. I presume it wasn’t just the battery recovery you were using.
Well, as I mentioned earlier, I re-tested a Astrolux C8 (FET driver with Samsung 30Q) that I’ve used for about 15-20 hours on max output over the past year-and-a-half. It gave the same output as when it was new.
However, my measurements are much less accurate than the 1% or 2% that djozz was talking about. And I’m not sure how much output variance clemence was seeing.
With the abundance of high quality copper MCPCB’s, my question is
Now are these boards comparable like Noctigon or KD for hold high Current and quality finiture?
I have checked quite a few DTP boards over time and they perform close to each other, and are at least all thermally way better than non-DTP boards.
Good to say Djozz,I hope also they will be perfect flat
without imperfections especially on the edges
where I found stairs on alu board time ago,had sanded