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Dead LEDs
by Apptech
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Getting White LEDs with long lifetimes is easy. Getting them
at a low cost is another matter. I've been testing various white LEDs for longevity and been getting some rather bad results from Chinese sourced products. Reports from others testing LEDs for the same purpose are similar. This is not a total surprise as the general received wisdom is that this is the case. It is however a somewhat surprise as it is not obvious why the Chinese products should tend to be so bad. A Chinese supplier (name will not be stated) even made some changes to try and meet my spec and the results were no better. By Chinese I mean companies that are Chinese based - NOT known internationals who are domiciled elsewhere but may use Chinese manufacturing (eg Avago, Cree, Nichia, ...) - such companies are demonstrably more liable to get it right. The universal claim is that white LEDs last 100,000 hours. I can assure you that many don't come anywhere close (by 2+ orders of magnitude in some cases). My questions are: - What mechanism makes Chinese LEDs so bad? - Why is this allowed to be? ie why don't they do whatever it takes to fix it. If anyone feels that my statements are a generalisation and that some Chinese white LEDs do have the sort of lifetimes one would expect then *PLEASE* do tell me the brands!. I'd be extremely happy to be wrong and to be able to source LEDs at non-market-leader prices. For white phosphor LEDs (blue radiator and yellow phosphor re-radiator) the degradation mechanism seems to be actual LED die output level. A possible mechanism in some cases MAY be die over-temperature due to excessive over-rating of die current capabilities. Phosphor death does not seem to be an issue in what I have seen. (it is in some other cases). Die bonding adhesive to the LED structure cup is claimed to be a problem in some cases but when this was changed in the LEDs I was getting to a Japanese sourced bonding product of good parentage it made about zero difference. Interestingly, and not directly related, some name brand LEDs give atrocious spectral results at very low currents while others are about as good across a wide range of currents. Russell -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by Wouter van Ooijen
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> The universal claim is that white LEDs last 100,000 hours. I
> can assure you that many don't come anywhere close (by 2+ > orders of magnitude in some cases). Just out of interest: how do you test this? 100.000 minus 2 orders of magnitude is 41 days, that's testable (with some patience), but how do you test 410 days? Or are there known relations between lifetimes at various currents? -- Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: www.voti.nl consultancy, development, PICmicro products docent Hogeschool van Utrecht: www.voti.nl/hvu -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by arocholl
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Mind you to ellaborate a bit on how you test LEDs for longevity?
How do you accelerate the process to understand 100K hours is wrong or what variables/instrument do you use to measure performance? 2008/7/16 Apptech <apptech@...>: > Getting White LEDs with long lifetimes is easy. Getting them > at a low cost is another matter. > > I've been testing various white LEDs for longevity and been > getting some rather bad results from Chinese sourced > products. Reports from others testing LEDs for the same > purpose are similar. This is not a total surprise as the > general received wisdom is that this is the case. It is > however a somewhat surprise as it is not obvious why the > Chinese products should tend to be so bad. A Chinese > supplier (name will not be stated) even made some changes to > try and meet my spec and the results were no better. > > By Chinese I mean companies that are Chinese based - NOT > known internationals who are domiciled elsewhere but may use > Chinese manufacturing (eg Avago, Cree, Nichia, ...) - such > companies are demonstrably more liable to get it right. > > The universal claim is that white LEDs last 100,000 hours. I > can assure you that many don't come anywhere close (by 2+ > orders of magnitude in some cases). > > My questions are: > > - What mechanism makes Chinese LEDs so bad? > > - Why is this allowed to be? ie why don't they do whatever > it takes to fix it. > > If anyone feels that my statements are a generalisation and > that some Chinese white LEDs do have the sort of lifetimes > one would expect then *PLEASE* do tell me the brands!. I'd > be extremely happy to be wrong and to be able to source LEDs > at non-market-leader prices. > > For white phosphor LEDs (blue radiator and yellow phosphor > re-radiator) the degradation mechanism seems to be actual > LED die output level. A possible mechanism in some cases MAY > be die over-temperature due to excessive over-rating of die > current capabilities. Phosphor death does not seem to be an > issue in what I have seen. (it is in some other cases). Die > bonding adhesive to the LED structure cup is claimed to be a > problem in some cases but when this was changed in the LEDs > I was getting to a Japanese sourced bonding product of good > parentage it made about zero difference. > > Interestingly, and not directly related, some name brand > LEDs give atrocious spectral results at very low currents > while others are about as good across a wide range of > currents. > > > > Russell > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- Ariel Rocholl Madrid, Spain -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by joseph@kirtland.com
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I am most curious, and perhaps someone can answer. You mention that the
white LED might fail within a 2x magnitude of 100k hours. 100k hours is about 11.4 years. How is MTBF estimated or calculated? I don't think they light an LED at its recommended current and wait - white LEDs haven't been around that many years. I've bought many of those 100 LED collections off ebay, some with a clear lens, others with the phosphor. In my case they are primarily for hobbyist use so gradual failure isn't as big a concern for me. Joe Apptech wrote: > Getting White LEDs with long lifetimes is easy. Getting them > at a low cost is another matter. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by Shawn Tan Ser Ngiap
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On Wednesday 16 July 2008 15:21:58 Joe Bento wrote:
> I am most curious, and perhaps someone can answer. You mention that the > white LED might fail within a 2x magnitude of 100k hours. 100k hours is > about 11.4 years. How is MTBF estimated or calculated? I don't think > they light an LED at its recommended current and wait - white LEDs > haven't been around that many years. Voodoo?? <grins/> -- with metta, Shawn Tan Aeste Works (M) Sdn Bhd - Engineering Elegance http://www.aeste.net -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by Richard-177
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I have spent some time in Chinese semiconductor manufacturing. I found that
some had very low yields. I found that keeping contamination out of the clean rooms was in some cases a challenge. Running the clean room below "clean" can result in below speck product. ----- Original Message ----- From: "Ariel Rocholl" <foros@...> To: "Microcontroller discussion list - Public." <piclist@...> Sent: Wednesday, July 16, 2008 10:08 AM Subject: Re: [EE]:: Dead LEDs > Mind you to ellaborate a bit on how you test LEDs for longevity? > > How do you accelerate the process to understand 100K hours is wrong or > what > variables/instrument do you use to measure performance? > > 2008/7/16 Apptech <apptech@...>: > >> Getting White LEDs with long lifetimes is easy. Getting them >> at a low cost is another matter. >> >> I've been testing various white LEDs for longevity and been >> getting some rather bad results from Chinese sourced >> products. Reports from others testing LEDs for the same >> purpose are similar. This is not a total surprise as the >> general received wisdom is that this is the case. It is >> however a somewhat surprise as it is not obvious why the >> Chinese products should tend to be so bad. A Chinese >> supplier (name will not be stated) even made some changes to >> try and meet my spec and the results were no better. >> >> By Chinese I mean companies that are Chinese based - NOT >> known internationals who are domiciled elsewhere but may use >> Chinese manufacturing (eg Avago, Cree, Nichia, ...) - such >> companies are demonstrably more liable to get it right. >> >> The universal claim is that white LEDs last 100,000 hours. I >> can assure you that many don't come anywhere close (by 2+ >> orders of magnitude in some cases). >> >> My questions are: >> >> - What mechanism makes Chinese LEDs so bad? >> >> - Why is this allowed to be? ie why don't they do whatever >> it takes to fix it. >> >> If anyone feels that my statements are a generalisation and >> that some Chinese white LEDs do have the sort of lifetimes >> one would expect then *PLEASE* do tell me the brands!. I'd >> be extremely happy to be wrong and to be able to source LEDs >> at non-market-leader prices. >> >> For white phosphor LEDs (blue radiator and yellow phosphor >> re-radiator) the degradation mechanism seems to be actual >> LED die output level. A possible mechanism in some cases MAY >> be die over-temperature due to excessive over-rating of die >> current capabilities. Phosphor death does not seem to be an >> issue in what I have seen. (it is in some other cases). Die >> bonding adhesive to the LED structure cup is claimed to be a >> problem in some cases but when this was changed in the LEDs >> I was getting to a Japanese sourced bonding product of good >> parentage it made about zero difference. >> >> Interestingly, and not directly related, some name brand >> LEDs give atrocious spectral results at very low currents >> while others are about as good across a wide range of >> currents. >> >> >> >> Russell >> >> >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > > > -- > Ariel Rocholl > Madrid, Spain > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by Spehro Pefhany
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Quoting Apptech <apptech@...>:
> Getting White LEDs with long lifetimes is easy. Getting them > at a low cost is another matter. > > I've been testing various white LEDs for longevity and been > getting some rather bad results from Chinese sourced > products. Reports from others testing LEDs for the same > purpose are similar. This is not a total surprise as the > general received wisdom is that this is the case. It is > however a somewhat surprise as it is not obvious why the > Chinese products should tend to be so bad. A Chinese > supplier (name will not be stated) even made some changes to > try and meet my spec and the results were no better. > > By Chinese I mean companies that are Chinese based - NOT > known internationals who are domiciled elsewhere but may use > Chinese manufacturing (eg Avago, Cree, Nichia, ...) - such > companies are demonstrably more liable to get it right. > > The universal claim is that white LEDs last 100,000 hours. I > can assure you that many don't come anywhere close (by 2+ > orders of magnitude in some cases). > > My questions are: > > - What mechanism makes Chinese LEDs so bad? Probably some technology they are not using. ;-) > - Why is this allowed to be? ie why don't they do whatever > it takes to fix it. Because it costs more to develop, buy or license the technology than it's worth to them. In which case you may find (as I have in some cases) that you're better off to buy the name brand products that have been forced down in price by the shoddy stuff. > If anyone feels that my statements are a generalisation and > that some Chinese white LEDs do have the sort of lifetimes > one would expect then *PLEASE* do tell me the brands!. I'd > be extremely happy to be wrong and to be able to source LEDs > at non-market-leader prices. > > For white phosphor LEDs (blue radiator and yellow phosphor > re-radiator) the degradation mechanism seems to be actual > LED die output level. A possible mechanism in some cases MAY > be die over-temperature due to excessive over-rating of die > current capabilities. Phosphor death does not seem to be an > issue in what I have seen. (it is in some other cases). Die > bonding adhesive to the LED structure cup is claimed to be a > problem in some cases but when this was changed in the LEDs > I was getting to a Japanese sourced bonding product of good > parentage it made about zero difference. There are more than one type of phosphor used in the blue-LED-plus-yellow phosphor configuration. Here is one commercial supplier: http://www.mt-berlin.com/frames_cryst/descriptions/led_phosphors.htm > Interestingly, and not directly related, some name brand > LEDs give atrocious spectral results at very low currents > while others are about as good across a wide range of > currents. > > > > Russell Out of curiosity, have you tried blue LEDs from the same suppliers? I'd be interested if they show a similarly short life. Blue (and white) LEDs have a relatively high voltage drop compared to other types such as superbright red, so the power dissipation at the junction can be twice as high at the same If. > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" s...@... Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by Spehro Pefhany
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Quoting Rich <rgrazia1@...>:
> I have spent some time in Chinese semiconductor manufacturing. I found that > some had very low yields. I found that keeping contamination out of the > clean rooms was in some cases a challenge. Running the clean room below > "clean" can result in below speck product. It's perhaps worth noting that with LEDs they sometimes have two grades-- one for export to first-world countries, and another for local toy manufacturers and sale to India, Bangladesh etc. where a 20% failure rate and wide variation is tolerated. Naturally the price of the third-world-rated floor sweepings is considerably lower. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" s...@... Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by Bob Axtell-3
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Russell,
The problem with the white LEDS is similar to problems with other Chinese goods (i.e. Li-Ion cells, many other items). The causes seems to be poorly-made chemicals. The raw chemicals used in many processes don't seem to be chemically pure enough for the task at hand. The labor is fine, the business practices are OK (but not to Western standards), but critical chemicals don't seem to be available. That's why a battery maker is able to make decent batteries for months then make a batch of really shoddy goods one week. That's what I was told when _I_ asked about it... --Bob On Wed, Jul 16, 2008 at 6:33 AM, Apptech <apptech@...> wrote: > Getting White LEDs with long lifetimes is easy. Getting them > at a low cost is another matter. > > I've been testing various white LEDs for longevity and been > getting some rather bad results from Chinese sourced > products. Reports from others testing LEDs for the same > purpose are similar. This is not a total surprise as the > general received wisdom is that this is the case. It is > however a somewhat surprise as it is not obvious why the > Chinese products should tend to be so bad. A Chinese > supplier (name will not be stated) even made some changes to > try and meet my spec and the results were no better. > > By Chinese I mean companies that are Chinese based - NOT > known internationals who are domiciled elsewhere but may use > Chinese manufacturing (eg Avago, Cree, Nichia, ...) - such > companies are demonstrably more liable to get it right. > > The universal claim is that white LEDs last 100,000 hours. I > can assure you that many don't come anywhere close (by 2+ > orders of magnitude in some cases). > > My questions are: > > - What mechanism makes Chinese LEDs so bad? > > - Why is this allowed to be? ie why don't they do whatever > it takes to fix it. > > If anyone feels that my statements are a generalisation and > that some Chinese white LEDs do have the sort of lifetimes > one would expect then *PLEASE* do tell me the brands!. I'd > be extremely happy to be wrong and to be able to source LEDs > at non-market-leader prices. > > For white phosphor LEDs (blue radiator and yellow phosphor > re-radiator) the degradation mechanism seems to be actual > LED die output level. A possible mechanism in some cases MAY > be die over-temperature due to excessive over-rating of die > current capabilities. Phosphor death does not seem to be an > issue in what I have seen. (it is in some other cases). Die > bonding adhesive to the LED structure cup is claimed to be a > problem in some cases but when this was changed in the LEDs > I was getting to a Japanese sourced bonding product of good > parentage it made about zero difference. > > Interestingly, and not directly related, some name brand > LEDs give atrocious spectral results at very low currents > while others are about as good across a wide range of > currents. > > > > Russell > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by Dr Skip
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Wouldn't that result in an _above_ speck product? :) and below spec... (sorry,
I couldn't resist). I can also add that since I run a lot of multi-white-LED items, that there is some percentage of individual LEDs that have died in a few hours of runtime rather than decades. No numbers or analysis after that, but enough to note and wonder why... Rich wrote: Running the clean room below > "clean" can result in below speck product. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by William "Chops" Westfield
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On Jul 16, 2008, at 10:35 AM, Dr Skip wrote: > some percentage of individual LEDs that have died in a few hours of > runtime > rather than decades. A fair number of the LED traffic lights around here have developed blotches of dead LEDs. Especially the white LEDs used for "Walk" signals, but also even RED lights. It's sorta sad; I bet someone in the local DoT is unhappy that the believed the "saves replacement costs" spiel.. BillW -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by Nate Duehr
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William "Chops" Westfield wrote:
> A fair number of the LED traffic lights around here have developed > blotches of dead LEDs. Especially the white LEDs used for "Walk" > signals, but also even RED lights. It's sorta sad; I bet someone in > the local DoT is unhappy that the believed the "saves replacement > costs" spiel.. They haven't replaced them though -- or you wouldn't have seen them. (GRIN) I suppose there's probably some rule about how many of them have to fail before the assembly has to be replaced. But agreed... everyone touted CFL's for home lighting so I've tried a few... all of which have failed in slightly longer lifespans than incandescent bulbs. (Continuing this on [EE] because I'm interested in the LIFESPAN engineering of these electrically engineered products... LEDs, CFLs, all the "stuff" that's supposed to last longer. Any discussion of CFL's as the saviors of the planet or whatever, should go to [OT] of course.) Nate -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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RE: Dead LEDs
by Paul Hutchinson
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> -----Original Message-----
> From: piclist-bounces@... On Behalf Of William "Chops" Westfield > Sent: Wednesday, July 16, 2008 4:33 PM > > A fair number of the LED traffic lights around here have developed > blotches of dead LEDs. Especially the white LEDs used for "Walk" > signals, but also even RED lights. It's sorta sad; I bet someone in > the local DoT is unhappy that the believed the "saves replacement > costs" spiel.. > > BillW I saw this happening soon after the LED lamps were introduced in SE Worchester County MA back about five years ago. Within a year a number of the lamps had been replaced and since then many have been replaced with the old incandescent type. A new traffic light was added on my commute a month ago and that town put up incandescent instead of LED, I'm guessing that town has given up on LED lights. >From a drivers perspective I'd like them to put them all back to incandescent because the LED units with multiple dead LEDs are very difficult to see in bright sunshine. I suspect the decreased light output when hot contributes to my difficulty in seeing some of them on hot commutes home. The town's around here seem to wait until they have more than 66% dead LEDs before they replace them. My guess as to why they are such a problem up here is that they failed to take into account the over 55 degC ambient temperatures inside a traffic light on a hot southern New England summer day. Add in all the heat from the LEDs and it wouldn't surprise me if on some days it's well over 80 degC in the light fixture. Paul Hutch -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by Richard Prosser
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Nate,
I've had good results with CFLs - especially on my garage door opener. This is a high vibration application and standard incandescent bulbs last about a month. "Rough Service" rated bulbs last about 6 months. I've had one CFL bulb fail at 2 weeks (internal dry joint) but one has lasted about 3 years so far and the other about 2 and it's replacement (so far) ~1year. In non "rough service" areas I've not had to replace any IIRC so better than 3 years and running. This is about 7 bulbs in addition to the ones in the garage. We still use incandescent where we have dimmers and in some less common fittings. Richard P 2008/7/17 Nate Duehr <nate@...>: > William "Chops" Westfield wrote: > >> A fair number of the LED traffic lights around here have developed >> blotches of dead LEDs. Especially the white LEDs used for "Walk" >> signals, but also even RED lights. It's sorta sad; I bet someone in >> the local DoT is unhappy that the believed the "saves replacement >> costs" spiel.. > > They haven't replaced them though -- or you wouldn't have seen them. (GRIN) > > I suppose there's probably some rule about how many of them have to fail > before the assembly has to be replaced. > > But agreed... everyone touted CFL's for home lighting so I've tried a > few... all of which have failed in slightly longer lifespans than > incandescent bulbs. > > (Continuing this on [EE] because I'm interested in the LIFESPAN > engineering of these electrically engineered products... LEDs, CFLs, > all the "stuff" that's supposed to last longer. Any discussion of CFL's > as the saviors of the planet or whatever, should go to [OT] of course.) > > Nate > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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Re: Dead LEDs
by Apptech
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> Dr Skip wrote:
>> some percentage of individual LEDs that have died in a >> few hours of >> runtime >> rather than decades. > BillW > A fair number of the LED traffic lights around here have > developed > blotches of dead LEDs. Especially the white LEDs used for > "Walk" > signals, but also even RED lights. It's sorta sad; I bet > someone in > the local DoT is unhappy that the believed the "saves > replacement > costs" spiel.. Where's the warranty document ... . Quite apart from actual LED longevity, poor driving can lead to early failures. Driving multiple LEDs while maintaining efficiency is a modest challenge that many do not rise to. I have seen many consumer products with little or no attempts to provide anything like constant current drive. Most 3-cell battery consumer torches place LEDs in parallel and across the battery. Some use a single shared series resistor. I have a 30? LED lantern powered by a 6V SLA with LEDs connected in pairs across the battery with no resistors. Works amazingly well. When you have many LEDs and a highish supply voltage available then multiple series parallel strings are possible. You'd HOPE that that was what eg traffic lights did. Using series resistors you get a degree of mismatch between strings and some losses in the resistors. For mains powered signalling equipment this is usually tolerable. For lighting applications the lumens/Watt suffer accordingly. When mains powered the voltage can vary substantially and if brightness and current are to be maintained at reasonably stable levels you need 'quite a lot of drop' [tm] in the series element. For battery powered equipment with multiple LEDs, if best possible efficiency is required then all LEDs need to be operated in a single series string with a (usually boost) converter used to provide appropriate voltage for desired current. With multiple series strings you need an indecently variable converter per string. Anything less gives suboptimum efficiency (assuming that all converters have the same efficiency). I have never yet seen equipment with multiple series strings and a converter per string. More on practical lifetime measuring later today ... . Russell -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
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