Led lifespan

Interesting article on leds. May help some decide how hard they want to push their leds. http://www.ledsmagazine.com/content/leds/en/articles/print/volume-9/issue-2/features/are-you-using-all-of-the-lumens-that-you-paid-for-magazine.html

The concept of using higher drive current also applies to LED families other than the XP-G. For example, the XLamp XM-L family is rated for 3000-mA maximum drive current. At 67% of maximum rated drive current (2000 mA), the TM-21 L70 projections yield a reported value of 36,300 hours based on 6000 hours of LM-80 testing. That 36,000-hour reported result is gated by the LM-80 test time and is valid across the LM-80 temperature range. But the calculated projections range from 2.3 million hours (at 45°C) to 160,000 hours (at 85°C).

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2.3 million hours!?

Finally the link.

Here is another 2012 publishing that is pretty good
http://www.aqualumaled.com/pdf/LED Behavior.pdf
Page 20 in the doc has the graph you want.

Nice link..just quickly went through it. Looks like they use the lm80 testing standard. Nice thing about the led magazine article is they show the lifespan adjusted for lower temperatures. Using big heatsinks and fans makes the lower numbers more applicable I think. Makes sense too after seeing how hot a 10 year warrantied cree led household bulb runs.

Efficiency is still king I think. But, there are things to look at considering driving harder. More watts from one reflected source may have less lumens per watt...but will have more lumens in total...driving further into canopy. So less efficient at producing lumens, but more efficient at projecting light further.

And if anything, at least another plus for quality leds. Keep them cool...and they will last a lot longer than 50,000 hrs..

Good info thnx pos. I have been frustrated that the Cree datasheets ignore the lower Tjs that many of our DIYs are running at. I have been aiming for less than 3% lumen depreciation in 3 years of 12/12 (13000 hours). At that point we could say, there virtually is no lumen depreciation. LM97

The article is suggesting that running soft is underutilizing the LED. I would agree with that regarding flashlights or lights that are used less frequently than grow lamps. But for our purposes, long hours in the grow room, running soft is more appealing. We can't see lumen depreciation but it shows up on our scales. Higher efficiency for a slightly higher up front cost = less heat, less AC, less heatsink, less driver and less electricity bill - good stuff.

I agree supra..it's why I'm doing my next build on the efficiency side. Running xmls at 2/3 max got my light more power in the available space. Running them at 1a would have took twice as much space and cost twice as much. Now with cobs..it's a different story. Cake and eat it too..lol.

What I took mostly from this wasn't overdriving them. It was how well top leds perform at max rated current and that led life is incredibly long if temperatures are controlled. Nothing that hasn't been heard before..I just like the way the article explained it.

Also, it seems, if someone wanted to do a simple as possible build they could mount one cob at max current and if kept reasonably cool still enjoy a long lifespan.

Anyone else noticed how these LEDs are at their best after 8000 hours of cool running.

I just assumed it was some kind of measurement error, but if not that is very interesting side effect

My personal cooling 'goal' would be to keep CXAs running at 1950 mA ,with their Tc under 50°C ...

Mr Flux ,those are case temperature indicated or junction temperatures ?
(maybe a silly question,but I'm too tired ,right now,to analyse the graph .... )

SupraSPL said:

I just assumed it was some kind of measurement error, but if not that is very interesting side effect

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The effect is real, Cree calls it dopant atom activation.

Mr Flux ,those are case temperature indicated or junction temperatures ?
(maybe a silly question,but I'm too tired ,right now,to analyse the graph .... )

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It's the case temperature.