Design Article
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dthayden
The manufacturers are probably not counting on the bulbs meeting the specified ...
elektryk321
A19 LED bulbs: What’s under the frosting?
Martine Simard-Normandin
7/19/2011 2:04 PM EDT
Bulb comparisons
The dimmable bulbs incorporate silicon-based Infineon or ST power transistors. We did not find silicon carbide technology in any of the lamps.
Each lamp uses a different LED driver IC. Pharox uses four ICs, 40 resistors and 16 capacitors, plus transformers and many diodes. All this to dim a 40-W-equivalent light bulb—but only, in some cases, if you purchase a new dimmer, since your old dimmer might not be compatible.
Philips uses a remote phosphor, relying on the bulb envelope material to do the wavelength conversion. Lutetium oxide is used as a fluorescent medium in more than one lamp. We have looked at many LEDs over the last few years and have never seen lutetium used before. More conventional phosphors, such as barium and cerium-doped YAG (yttrium aluminum garnet), are also seen, along with a cocktail of rare earths such as europium and strontium.
Surprisingly, everyone uses blue GaN LEDs—no RGB LEDs in this lot. There are red LEDs in the Pharox, complete with lenses, but they don’t turn on when the lamp is on. They are obviously not for color balance. Maybe the light turns red when the bulb is about to die, or to signal that the lamp is not wired properly.
Philips uses many of its own Luxeon Rebel LEDs in a modular arrangement that could possibly permit the replacement of failed modules. We expected the Sylvania to use an Osram LED, perhaps a Dragon, but that is not the case. Two of the lamps rely on Cree dice.
The LED light-emitting area varies from 4 mm2 to 12 mm2 for the 40-W equivalent bulbs—a variance of a factor of 3—yet their power consumption ranges between 6 and 9 W. Some have four LED dice; others have 48.
At what point is such a lamp considered to have reached the end of its operable life, given its dozens of individual LEDs? Nowhere on the fancy packaging, with all its warnings, disclaimers and warranties, is there a definition of the point of final failure for the lamp. Will it go out with a flash? Will it still be usable for its intended purpose until the last second, or will there be a point at which the light has become so faint that the user decides to replace the bulb?
Lots of questions, and we still haven’t answered the first one: Why are A19 LED bulbs so expensive? At 50 to 60 lumens/W, the LED bulbs have the same efficacy as 40-W-equivalent compact fluorescent lights, which typically offer 560 lumens at 10 W, can be purchased for a few dollars and should last, or so the packaging claims, up to eight years. For the same savings in electricity as you’d get with a single LED bulb, you would need to purchase two or three additional CFL bulbs over the next 25 years. Luckily they are available in packs of two or four.
Light bulbs are a commodity item, no matter how long they last. For all the claims of CFL longevity, I have yet to see them reach their expected lifetime. Usually the point of CFL failure is the electronics in the neck, and the same will likely hold true for LED bulbs.
With CFLs, however, we have traded energy consumption for mercury contamination. The attraction of LED bulbs is twofold: They are instant-on, and they are mercury free. The toxicity of rare earths is low, and very little of the material is used in the bulbs anyway.
Over time, LED bulbs will drop in price and will provide a cleaner, safer alternative to CFLs—presumably with a longer life expectancy as well. We can also expect new features; the door is fully open on that front.
About the author
Martine Simard-Normandin is president and CEO of MuAnalysis Inc. (Ottawa), a privately owned professional laboratory.
The dimmable bulbs incorporate silicon-based Infineon or ST power transistors. We did not find silicon carbide technology in any of the lamps.
Each lamp uses a different LED driver IC. Pharox uses four ICs, 40 resistors and 16 capacitors, plus transformers and many diodes. All this to dim a 40-W-equivalent light bulb—but only, in some cases, if you purchase a new dimmer, since your old dimmer might not be compatible.
Philips uses a remote phosphor, relying on the bulb envelope material to do the wavelength conversion. Lutetium oxide is used as a fluorescent medium in more than one lamp. We have looked at many LEDs over the last few years and have never seen lutetium used before. More conventional phosphors, such as barium and cerium-doped YAG (yttrium aluminum garnet), are also seen, along with a cocktail of rare earths such as europium and strontium.
Surprisingly, everyone uses blue GaN LEDs—no RGB LEDs in this lot. There are red LEDs in the Pharox, complete with lenses, but they don’t turn on when the lamp is on. They are obviously not for color balance. Maybe the light turns red when the bulb is about to die, or to signal that the lamp is not wired properly.
Philips uses many of its own Luxeon Rebel LEDs in a modular arrangement that could possibly permit the replacement of failed modules. We expected the Sylvania to use an Osram LED, perhaps a Dragon, but that is not the case. Two of the lamps rely on Cree dice.
The LED light-emitting area varies from 4 mm2 to 12 mm2 for the 40-W equivalent bulbs—a variance of a factor of 3—yet their power consumption ranges between 6 and 9 W. Some have four LED dice; others have 48.
 Click on image to enlarge. |
At what point is such a lamp considered to have reached the end of its operable life, given its dozens of individual LEDs? Nowhere on the fancy packaging, with all its warnings, disclaimers and warranties, is there a definition of the point of final failure for the lamp. Will it go out with a flash? Will it still be usable for its intended purpose until the last second, or will there be a point at which the light has become so faint that the user decides to replace the bulb?
Lots of questions, and we still haven’t answered the first one: Why are A19 LED bulbs so expensive? At 50 to 60 lumens/W, the LED bulbs have the same efficacy as 40-W-equivalent compact fluorescent lights, which typically offer 560 lumens at 10 W, can be purchased for a few dollars and should last, or so the packaging claims, up to eight years. For the same savings in electricity as you’d get with a single LED bulb, you would need to purchase two or three additional CFL bulbs over the next 25 years. Luckily they are available in packs of two or four.
Light bulbs are a commodity item, no matter how long they last. For all the claims of CFL longevity, I have yet to see them reach their expected lifetime. Usually the point of CFL failure is the electronics in the neck, and the same will likely hold true for LED bulbs.
With CFLs, however, we have traded energy consumption for mercury contamination. The attraction of LED bulbs is twofold: They are instant-on, and they are mercury free. The toxicity of rare earths is low, and very little of the material is used in the bulbs anyway.
Over time, LED bulbs will drop in price and will provide a cleaner, safer alternative to CFLs—presumably with a longer life expectancy as well. We can also expect new features; the door is fully open on that front.
About the author
Martine Simard-Normandin is president and CEO of MuAnalysis Inc. (Ottawa), a privately owned professional laboratory.|
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Hube
7/21/2011 1:16 PM EDT
Well done, interesting analysis, electrolytics are the main problem with CFL, as you state these LED will be poised with this too.
ACRICHE LED with direct AC input design are more quiet solutions, I have already 3 years of full time running,70 ACRICHE lamps involved and no defect. Control after one year shows no decrease.
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Tony41
7/21/2011 1:27 PM EDT
I have been developing LED lights for many years. I was the first to put them behind a LCD large flat screen for outdoor advertising in direct sunlight.
I would not purchase any of the LED light bulbs on the market today. The LED's may last a long time but the plastics and power supply components will not.
I designed and developed my own LED lights for my home because I could not find one I would purchase. I use long life components as well as RGB LED's to give me the color spectrum needed for proper lighting. I have also been able to get a bright light that is brighter than an equivalent 100 watt light bulb. I have experimented with quantum dots but it dimes the light too much to get a color shift.
I can dim them just by turning off a few LED’s at a time with a switch. I have an LED module that is 2” X 2” X 1/4” thick plugs directly into 120VAC as well.
I can also power them from batteries charged by a solar panel. During a power outage I have lights when all around me are black.
I can see why LED lighting is failing to gain traction in the US. I have been unemployed for over two years and cannot get a job, however just working at home I seem to be well ahead of all of you.
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musiklab
7/27/2011 4:19 AM EDT
Hi tony41.
sorry you´re out of a job. how about making one for yourself developing those ideas.
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Andrewier
7/21/2011 3:52 PM EDT
Great article! I also deeply agree with Tony41.
These new LED bulbs are the same kind of trash as currently available CFL. They are intended (supposedly) to replace standard incandescent bulbs. As most bulbs are installed hanging from the ceiling, usually inside a recess, you have your fragile electrolytic cap and other components subjected to the higher possible temp! Very smart engineering!!!
And c'mom, 3 to 4 hours a day? I have a couple of lamps around my house installed for safety reasons that stays on from sunset to sunrise (~7 PM to ~6 AM). You can imagine how will be the lifespan of these electronics, staying hot for 10+ hours in a row everyday...
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Robotics Developer
7/21/2011 11:22 PM EDT
I have been disappointed in both the cost and the working usefulness of the LED bulbs. Another thing that bothered me was (at least one brand) the lamp base was hot...seems to me if a light is generating heat it is wasting energy. I am amazed at the current cost for these bulbs and not at all happy with CFLs! The "working usefulness" issue for me is the directional-ness of these bulbs. They may work great in a reading lamp fixture or an overhead can (ignoring the heat concern) but for general lamp fixture use such as ceiling dome lights, floor/table lamps they do not shine the light in the right direction!! I am not yet going to use these and currently must suffer with CFLs to keep my electric costs down. At least with CFLs they are cheap.
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musiklab
7/27/2011 4:22 AM EDT
I have had many CFL bulbs, but small sizes don´t last anywhere near the 8000 hours promised.
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David Ashton
7/27/2011 5:32 AM EDT
I don't see why the electronics needs electrolytics. If you full wave rectify the AC, it should be possible to operate the LEDs only during each half-cycle - at 100 HZ the flicker should not be visible? You could still have a switch mode inverter running to power a string of LEDs at several tens or '00s of Kc during each half-cycle? Tony41, or any other hot shot designers, could you comment?
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David Ashton
7/27/2011 5:34 AM EDT
Sorry, I've always been in British type 50Hz AC areas. For you Yanks it will be 60 Hz / 120 Hz - even less chance of perceiving the flicker??
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VZwanenberg
8/15/2011 8:39 AM EDT
Hi David,
I've several years experience in drivers for LED lamps, and did investigate visible and non-visible flicker. Next link provides my input for Energystar guidelines on LEDlamps and light modulation.
http://www.energystar.gov/ia/partners/manuf_res/downloads/lighting/NXP_Semiconductors_Comments.pdf
With regards,
Victor Zwanenberg
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Battar
7/27/2011 6:48 AM EDT
I bought a LED desk lamp recently which runs off a switching "wall wart" type 20W supply. The separate PSU is probably good for 50000 hours. The way forward with LED lamps is probably to decouple the bulb from the power supply - the low voltage DC supply should be part of the lamp socket, not the lamp itself.
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David Ashton
7/31/2011 7:15 AM EDT
Good idea - there are CFL fittings that work like this, the 2-pin lamp has the tube and the starter and the ballast is separate. There are also 4-pin types for electronic ballasts. So same idea should be good with LEDs - and reduce the ongoing cost a bit maybe.
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WKetel
7/27/2011 3:11 PM EDT
An interesting question as to why need electrolytic capacitors. A portion of the problem is indeed avoiding flicker, although I am not convinced that a small PP capacitor right behind the line rectifier would not be adequate. Of course one other challenge is the emphasis on absolute minimum BOM cost, notwithstanding the quality problems that result. One dollar more to assure the 50K hour lifetime would be quite reasonable to me.
What I think to be very interesting would be a cost breakdown on the various devices, since I doubt that any of them has over $5 in electronic parts, and I am talking Digikey prices. Knowing just where the cost lies would be a very good start.
I have also wondered about why nobody markets an LED device that uses the rectified line voltage and a current limiting resistor, and perhaps 80 or a hundred "fairly bright" surface mount, or even through hole, LEDs. No filtering, just leds on the full wave rectified line, with 120HZ flicker, which I don't think we could see. Does anyone see a fundamental problem with that?
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Hube
8/1/2011 3:49 PM EDT
Read my comment, the fist one. ACRICHE is the answer you ask for. Seoul is not the only one maker of these devices. Tree years, 70 lamps always on, no defect, in a few days 2 millions cumuled hours !
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antiquus
8/22/2011 11:27 AM EDT
Do you think the mfg cares about 50k hour lifetimes? A 3k lifetime (1/2 year @100%) would be enough to outlast the thermal-printing on the home depot receipt.
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Mongo647
7/27/2011 4:20 PM EDT
Have you seen the flicker in the original Oriental LED christmas lights, done as you suggest? Psychedelic with any movement of your head. Festive but not so good for studying engineering textbooks.
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David Ashton
7/28/2011 12:07 AM EDT
I guess Incandescents have a good bit of thermal inertia and don't dim much if at all in between half cycles.
TV's would also have a bit of persistence on the phosphor...and CFLs also usually have an electrolytic in them. Whereas LEDs would definitely be on-off devices.
Memo to self...when studying engineering textbooks, do not move head.... ;-)
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chris.michael
7/28/2011 7:30 PM EDT
Those would be directly emmitting diodes then. These diodes shine onto phosphors to make white light. The phosphors continue to glow for brief period after the diode stops emmiting and might be able to mask the flicker. We ran into a problem with white LEDs on a system that was trying to blink at a 50% duty cycle only to have the phosphor glow distort it.
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MVSEENAN
7/31/2011 3:57 AM EDT
Hi I am from India and developed LED lamp that works out from the regular incandecent bulb sockets.All led bulbs require Electronics to step down the voltage as they work on 3.3 to 4 volts only.As the current requirements are more heat will be developed and cannot be avoided.The led may last more but the electronics is bound to fail soon than claimed.
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Amcfarl
8/1/2011 11:49 AM EDT
Electrolytics are available which survive 12,000 hours at 105C. Unless you are cooking your LED's then you can get extremely long lifetimes and my own patented 900 lumen, 90+lumens/w 60W equivalent dimmable design exceeds 98% efficiency so almost no heat from the driver. And all that with 0.993 PF excellent coliur rendering and NO EMI!
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liteman
9/18/2011 9:13 AM EDT
Can you please tell me more about your patent, is it pending ?
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Amcfarl
1/20/2012 4:00 PM EST
Hi 'Liteman',
I just picked up your query about my design. Yes it is still an application but has no objection raised as yet. It applies to UK, Europe and USA. If you can tell me a little more about what you'd like to know I'd be happy to help. e1aam@surfree.co.uk
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elektryk321
8/20/2012 9:28 AM EDT
I have two remarks:
1. 105*C capacitors are commonly used in PC power supplies and PC mainboards. They still die in much lower temperature than 105*C.
2. 105*C capacitors are more expensive than typical one (like 85*C). I don't think if typical LED bulb goes higher than 80*C, so why someone should use 105*C capacitors?
I guess problem is not in high temperature but capacitor quality.
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pyeatte
8/17/2011 12:40 PM EDT
Until light wiring and distribution is low voltage instead of 120vac, we will have these problems.
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elwood
11/22/2011 3:10 PM EST
Application specific Power sources!
Is anyone aware of a Roadmap for power? Do the benefits of various power sources make $$ sense?
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Sanjib.Acharya
8/28/2011 12:50 AM EDT
I've liked this article as it has answered the same question I had: Why the LED lamps are so costly and I understand, more than electronics, the manufacturers need to do something on the heat management and the casing part to bring down the cost.
Like many of my fellow readers, I am also surprised to see the claim of high lifetime with the electrolytic capacitors in it.
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StuRat
9/20/2011 12:15 PM EDT
A concern that I don't see addressed is vibration. I have had a CFL blowout in a ceiling fan installation. I haven't seen vibration ratings for CFLs. I These board designs with the air-chassis electrolytics don't look to have reliability in a vibration environment such as a ceiling fan fixture.
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phlei
2/3/2012 4:39 PM EST
If you develop a PFC LED driver, you can use the deramic cap instead of the E-Cap. The E-cap life time shrinks one half for every ten degree ambient temperature. We have been designed the ACDC offline LED drivers for the LED lighting and to reduce the BOM cost. If you are interested in the products, please check out the web site.
www.sqme.com.tw
We design our products in the 700V process, so the 500V HV NMOS and the 700V Power MOSFET can be integrated.
Please send email to Phil.Lei@sqme.com.tw to find out more.
Best Regards,
-Phil
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dthayden
2/4/2013 6:00 PM EST
The manufacturers are probably not counting on the bulbs meeting the specified life but rather replacing them in the future with cheaper to manufacture products. Or just counting on consumers to not follow up with early failure replacements, as we were trained to accept with CFL bulbs which failed to live up to the marketing claims.
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