NewBie
*Retired*
Many have asked, some actual data I ran across (FYI, these are Nichia 5mm LEDs):
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5mm overdrive degradation data
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Wow. Very informative. Thanks. It'd be cool to also have 20mA data as well. Lumileds has 10K hours of data on 5mm LEDs (driven at spec, I'm sure), it'd be neat to have that overlayed as well. The data is in this document:
http://www.luxeon.com/pdfs/RD25.pdf
Page 4
http://www.luxeon.com/pdfs/RD25.pdf
Page 4
NewBie
*Retired*
You can draw a line from 100 to 80% at 1000 hours for 20mA drive. If a fella overdrives them, they degrade faster and faster, the more they are overdriven... Primary factor is heat. My Nichia fella said to use 296 to 350 C/W for the thermal resistance from die to lead, and then one needs to also add in the C/W of the lead to ambient. From my own testing, the C/W from lead to ambient is also a major factor, as heat is the #1 degradation mechanism- which has been proven over and over...phosphor degradation is #2 (in 5mm LEDs). Though, die attach adhesive can be the biggest culprit of for some of the LEDs that are not made well-heat and wavelength affect the die attach adhesives. You'll find CREE and LumiLEDs soldering their die instead of utilizing adhesives...
Right, I have a graphic here:
Right, I have a graphic here:
NewBie said:
Good info. I've seen other data that shows Nichia's degrading considerably slower than any other 5mm brand, so just wonder how quickly the other brands degrade when overdriven.
BTW, are the CREE and Lumileds die larger? If so, that may be a primary reason why they use solder over epoxy/adhesives. Most assembly houses have problems controlling solder volume to minute scales and smaller die have a tendency to tilt, twist, or even shorted (solder creepage too high up the sides of the die) so smaller die tend to use epoxy (which also has a limit on die size being too small). Also, since 5mm are lower power, the justification and cost for solder is harder, tho solder is a better heat conductor (needed and thus more justified for higher power LEDs).
Ty_Bower
Flashlight Enthusiast
evan9162 said:
Old LEDs don't die, they just... fade away.
eebowler
Flashlight Enthusiast
This is upsetting. I've always had the impression that 5mm LEDs had a significantly higher lumens maintenance than high power LEDs even though they had no noticable means of getting rid of heat. Graph two proves otherwise. 
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ViReN
Flashlight Enthusiast
NewBie said:Many have asked, some actual data I ran across (FYI, these are Nichia 5mm LEDs):
are these Nichia CS LED's ?
I have emailed Mr. Narendran and awaiting response
NewBie
*Retired*
Viren, they are the 510BS LEDs. It really isn't going to make a whole lot of difference. You still have the thermal resistance from the die to the cup, then down the lead that runs out of the 5mm package. It is in the 300-350 C/W range.
When you over drive these at all, they are going to degrade *much* more rapidly.
The lifetime of white LEDs has never been a secret. It has been published widely since 2002 that they degrade fast, and the degradation rate accellerates *extremely* fast in overdrive. Absolutely nothing at all new about this.
Now there have been alot of folks running around, ill-informed, making up stuff about 100,000 hours. I asked the major players about this, and it was big news to them. When pushed, one of the manufacturers provided this official factory testing information:
You don't remember when folks used to keep asking Gransee about what he did to his new ARC AA/AAA, as they kept saying that it is so much brighter than my old one!!! It wasn't, it was the LED in the old one had degraded so rapidly.
No, it is not the high power LEDs that have the rapid degradation. They can degrade fast, if you over drive them, or have poor heatsinking, or both (which is really bad). There is a reason for specs, and if one doesn't understand them, they are bound to have issues. It is the 5mm white LEDs that have the very rapid degradation.
However, if you underdrive the 5mm LEDs (1-5mA), I have data that shows their lifetime can be *greatly* extended. Additionally, if the leads are soldered to copper slabs, right where they come out of the package (not 3mm later...), and heatsinks are added, and you use 30cfm of air on the heatsink, their life can be additionally increased on top of the underdrive, rather significantly yet again.
Arrays of like three 5mm LEDs, that are closely spaced (say at 1 cm spacing) are a very bad idea, as the heat by the nearby LEDs makes matters even worse, and things compound alot. Its kinda like riding a pissed off bull that is being stung by hornets heading for the safety of a barn that is on fire while an earthquake is in progress. It gets much worse for arrays of more than three.
If you chop off the leads, when you solder them flush on a pcb (which is usually FR-4/G-10), things get even worse. The copper layer is typically 0.000707" thick, and as such, provides really **** poor heatsinking.
Oh, yeah, and their lm/W numbers go to hell in a hen basket when over driving, even just a little bit.
When you over drive these at all, they are going to degrade *much* more rapidly.
The lifetime of white LEDs has never been a secret. It has been published widely since 2002 that they degrade fast, and the degradation rate accellerates *extremely* fast in overdrive. Absolutely nothing at all new about this.
Now there have been alot of folks running around, ill-informed, making up stuff about 100,000 hours. I asked the major players about this, and it was big news to them. When pushed, one of the manufacturers provided this official factory testing information:
You don't remember when folks used to keep asking Gransee about what he did to his new ARC AA/AAA, as they kept saying that it is so much brighter than my old one!!! It wasn't, it was the LED in the old one had degraded so rapidly.
No, it is not the high power LEDs that have the rapid degradation. They can degrade fast, if you over drive them, or have poor heatsinking, or both (which is really bad). There is a reason for specs, and if one doesn't understand them, they are bound to have issues. It is the 5mm white LEDs that have the very rapid degradation.
However, if you underdrive the 5mm LEDs (1-5mA), I have data that shows their lifetime can be *greatly* extended. Additionally, if the leads are soldered to copper slabs, right where they come out of the package (not 3mm later...), and heatsinks are added, and you use 30cfm of air on the heatsink, their life can be additionally increased on top of the underdrive, rather significantly yet again.
Arrays of like three 5mm LEDs, that are closely spaced (say at 1 cm spacing) are a very bad idea, as the heat by the nearby LEDs makes matters even worse, and things compound alot. Its kinda like riding a pissed off bull that is being stung by hornets heading for the safety of a barn that is on fire while an earthquake is in progress. It gets much worse for arrays of more than three.
If you chop off the leads, when you solder them flush on a pcb (which is usually FR-4/G-10), things get even worse. The copper layer is typically 0.000707" thick, and as such, provides really **** poor heatsinking.
Oh, yeah, and their lm/W numbers go to hell in a hen basket when over driving, even just a little bit.
InfidelCastro
Banned
evan9162 said:
Marketing people.
NewBie
*Retired*
InfidelCastro said:
Most especially flashlight marketing people.
For 5mm white LEDS, the main source of light degradation IS NOT heat. Heat certainly plays a major impact when you start talking about LEDs life being reduced into the 5-10K hour life, but white 5mm LEDs have significant degredation at as little as a couple hundred hours into the low thousands of hours.
This quick degradation occurs due to the yellowing of the epoxy encapsulation used in 5mm LEDS. The phosphor essentially "traps" the blue light near the phosphor causing rapid degredation of the epoxy. Almost all high powered LEDS and some mid-power surface mount LEDS use silicon encapsulation. This was one of the big advances that Lumileds brought to the market. This eliminated the rapid degredation of white LEDS. To get the 50K+ hours at 70% light output, of course lots of other things are needed such as good thermal management of the die, robust die structures that do not cause any "hot spots" due to current crowding, etc. It is difficult to even get reputable LED suppliers like Cree and Nichia to give you a very clear statement of how long their LEDs will last at a given die temperature. For the no name guys, they just say 100K hours on their data sheets but with little or no description under what conditions this will occur.
The Luxeon and Luxeon3 dies were attached with solder, but I think the new K2 uses a different die attach method.
Semiman
This quick degradation occurs due to the yellowing of the epoxy encapsulation used in 5mm LEDS. The phosphor essentially "traps" the blue light near the phosphor causing rapid degredation of the epoxy. Almost all high powered LEDS and some mid-power surface mount LEDS use silicon encapsulation. This was one of the big advances that Lumileds brought to the market. This eliminated the rapid degredation of white LEDS. To get the 50K+ hours at 70% light output, of course lots of other things are needed such as good thermal management of the die, robust die structures that do not cause any "hot spots" due to current crowding, etc. It is difficult to even get reputable LED suppliers like Cree and Nichia to give you a very clear statement of how long their LEDs will last at a given die temperature. For the no name guys, they just say 100K hours on their data sheets but with little or no description under what conditions this will occur.
The Luxeon and Luxeon3 dies were attached with solder, but I think the new K2 uses a different die attach method.
Semiman
NewBie
*Retired*
SemiMan said:
Humm, don't you realize that epoxy degrades on exposure to heat?
You should read a few of Mr. Narendran's papers where he studied the degredation mechanism, and himself, said it was heat, amongst other things. It is the heat that affects the epoxy, combined with the short wavelength light.
Even more so, it is good to recognize that it has been shown repeatedly that blue LEDs actually degrade slower than White LEDs. This is counter-intuitive, if the major mechanism is due to the short wavelengths involved...as the White LED's phosphor actually convert a large portion the blue to longer wavelengths. Visit the link below, under "Journal of Crystal Growth 268 (3-4): 449-456".
I have just the critter under test right now, where I've *very* agressively addressed the heat issue, and they are running out past 20,000 hours now, and it will be a very long time before they cannot make the required light level. My testing has actually been in process since 2001.
IEEE/OSA Journal of Display Technology, Vol. 1, No. 1, September 2005
Life of LED-Based White Light Sources
Nadarajah Narendran and Yimin Gu
"Even though light-emitting diodes (LEDs) may have a very long life, poorly designed LED lighting systems can experience a short life. Because heat at the p-n juncion is one of the main factors that affect the life of the LED, by knowing the relationship between the life and heat, LED system manufacturers can design and buld long-lasting systems."
http://www.lrc.rpi.edu/programs/solidstate/pdf/narendran-gu-JDT2005.pdf
Journal of Crystal growth, Vol 268, No. 3-4, pp. 449-456, August 2004
Solid-State lighting" failure analysis of White LEDs.
Nadarajah Narendran and Yimin Gu and L. Deng
"Therefore, based on past studies, the primary reason for the degradation of indicator-style white LED packages is the yellowing of the epoxy that is caused by excessive heat at the p-n junction of the LED.
Society of Photo-Optical Instrumentation Engineers
Third International Conference on Solid State Lighting, Proceedings of SPIE 5187: 107-114
Nadarajah Narendran and Yimin Gu
"Therefore, based on past studies, the primary reason in the degradation of 5mm white LEDs is the yellowing of the epoxy due to thermal effects."
http://www.lrc.rpi.edu/programs/solidstate/pdf/NonContactMethod.pdf
International Society of Optical Engineers
Fourth International Conference on Solid State Lighting, Proceedings of SPIE 5530
White LED Performance
Yimin Gu, Nadarajah Narendran, and Jean Paul Freyssinier
"Tests of 5mm white LED arrays showed that junction temperature increases produced by dirve current had a greater effect on the rate of light output degradation than junction temperature increases from ambient heat...The dissimilarity in temperature effect among 5mm and high-flux LEDs is likely caused by packaging differences between the two device types."
http://www.lrc.rpi.edu/programs/solidstate/pdf/guSPIE.pdf
Journal of Crystal Growth 268 (3-4): 449-456
N. Narendran, Y. Gu, J.P. Freyssinier, H. Yu, and L. Deng
Failure Analysis of White LEDs
Experimental results showed that the degradation rate depends on both the junction temperature and the amplitude of short-wavelength radiation. However, the temperature effect was much greater than the short-wavelength amplitude effect.
http://www.lrc.rpi.edu/programs/solidstate/pdf/narendran2004_jcrystalgrowth.pdf
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jtr1962
Flashaholic
Don't you mean to say that blue LEDs degrade slower than white ones? My guess for the reason is that the conversion to white light of the phosphor in white LEDs produces some heat as a byproduct over and above that emitted by the blue die itself. This means for any given drive level white LEDs run hotter than blue ones with an identical chip, and hence degrade faster.NewBie said:
Can you share your data? I have a project in the future where I'm already underdriving the LEDs at 10 mA for longer life. Will the life be extended significantly by coming down to 5 mA instead?
Regarding this whole subject, it shouldn't be terribly hard or terribly expensive to change the packaging used in 5mm LEDs slightly so that there is a better thermal path, and to use epoxy formulations which are resistant to both short wavelength light and heat, again for little if any cost penalty. I for one would certainly be willing to pay a few pennies more per 5mm LED if it they really did take 100,000 hours or more to reach 50% brightness.
On another note, if heat is the primary degradation mechanism then eventually more efficient chips should solve the problem. If you can get power to light conversion efficiency to approach 100% then there is virtually no heat in the LED package.
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BentHeadTX
Flashlight Enthusiast
I am glad I converted to all Luxeon LEDs with my most used lights. 5mm LEDs are great for their original design but not overdriven in flashlights. (See ranting in the Proton review) Still use 5mm lights for red/UV when needed so no major worries about every wearing them out.
For existing lights, it might be a good idea to go with NiMH instead of lithiums to drop the drive levels. Peter had better get moving on the Luxeon AAA model.
For existing lights, it might be a good idea to go with NiMH instead of lithiums to drop the drive levels. Peter had better get moving on the Luxeon AAA model.
NewBie
*Retired*
jtr1962 said:
Yes, thanks. Fixed.
jtr1962
Flashaholic
Indicator lights running at 5 to 20 mA. Once LEDs were bright enough to be used for illumination instead of indication the desire came along to make them even brighter by overdriving. The 5mm package just isn't up to the demands of running at more than 20 to 30 mA. Also, blue (and white) LEDs have a higher Vf than the original red, amber, orange, and yellow, so this results in yet more power being dissipated even at 20 mA compared to the older LEDs.Archangel said:
The so-called superflux LEDs have a much better thermal path and as a result should last longer for a given current level compared to 5mm LEDs. I'll point out that 5mm LEDs still have plenty of uses even for illumination provided one is aware of their limitations. A Luxeon is wasted on a device only requiring a few lumens, for example.
NewBie
*Retired*
So folks don't get confused, 5mm LEDs and SuperFlux LEDs are quite different creatures. The SuperFlux LEDs have a very large metal pad inside, with multiple leads, which greatly enhances their thermal properties and allows you to drive them up at 50-70mA without severely degrading the LED. They are also known as Spider LEDs, but not all are created equal.
http://www.lumileds.com/products/line.cfm?lineId=4
I have seen these in white, but I don't remember who made a white version in this package.
There is also the SnapLED, which is designed for 70-150mA, but is only available in the reds:
http://www.lumileds.com/pdfs/DS08.PDF
http://www.lumileds.com/products/line.cfm?lineId=4
I have seen these in white, but I don't remember who made a white version in this package.
There is also the SnapLED, which is designed for 70-150mA, but is only available in the reds:
http://www.lumileds.com/pdfs/DS08.PDF
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