Author Topic: Why/how do these LED lamps fail so fast?  (Read 5290 times)

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Offline soldarTopic starter

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Why/how do these LED lamps fail so fast?
« on: September 20, 2023, 04:49:28 pm »
We are told LED lights are eternal and will last more than 10,000 incandescent lamps but not in my experience.

About a year BP (Before the Pandemic) I bought a bunch of round flat ceiling LED lights and I installed some of them in a second home where I do not spend that much time. Today the third one out of seven has failed. They all fail in the same way. The flicker but do not start up. The symptoms are that the PSU is failing but it is the string of LEDs that fails and the PSU is fine. If I exchange PSUs between lamps the problem stays with the lamp, not the PSU.

I do not know how to interpret these symptoms except that the LEDs are demanding more current and the PSU is limited and shuts down. So I have three PSUs to play with.  I am talking from memory but IIRC they provide a constant current of about 240 mA at about 60V. Not isolated from mains so care is recommended.

I am assuming the LEDs fail because they are being driven too hard. But for the brief moment they are on I do not see any one of them not lighting.

This time I might test the string of LEDs with a DC power supply (which I do not have and will have to rig).

My experience with LED lamps is not being good. And what ticks me off is that these are complete ceiling fixtures where you can't just change the light-bulb like in the good old days.

Any ideas or knowledge on this topic?

I am thinking that, with a constant current PSU, I could divert some of the current through a resistor in parallel and this would lower the dissipation in the LEDs. Suppose it is putting 240 mA at 60 V. If I put in parallel a 2K4 resistor it will take away 25 mA from the LEDs (and dissipate 1.5W).

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Offline Grandchuck

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Re: Why/how do these LED lamps fail so fast?
« Reply #1 on: September 20, 2023, 05:06:12 pm »
I don't know if it is relevent to your lights, but if an LED in a series string shorts out the others draw more current if the power supply is a CV type.
 

Offline artag

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Re: Why/how do these LED lamps fail so fast?
« Reply #2 on: September 20, 2023, 07:19:44 pm »
Big Clive often autopsies (biopsies ? some aren't broken when he starts) LED lamps and looks into the current control. Often, there is a resistor whose value sets the LED current.

A while ago he investigated some Philips lamps only available in Dubai which were underrun for longer life. So he often explains how a given lamp can be modified to run at lower current.
 

Offline soldarTopic starter

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Re: Why/how do these LED lamps fail so fast?
« Reply #3 on: September 20, 2023, 08:02:58 pm »
I don't know if it is relevent to your lights, but if an LED in a series string shorts out the others draw more current if the power supply is a CV type.
I was thinking along those lines. If one LED fails open then none will light. If it fails shorted then the other will draw more current  depending on the PSU. This one seems to be more like constant current, variable voltage. If one or more LEDs short out then the current should stay the same but the voltage should drop. It could be that if the voltage drops then the PSU shuts down as detecting a short.

But, without looking too closely, I did not see any individual LEDs obviously not lighting.

I think I need to do some more testing with both the LED string and with the PSU.
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Offline dobsonr741

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Re: Why/how do these LED lamps fail so fast?
« Reply #4 on: September 20, 2023, 08:07:04 pm »
I saw electrolytics causing the trouble many times. Usually, the simple plastic encased bulbs. So my working theory is overheating, caps blowing up or getting leaky and cascading into semiconductor and LED failure.
 

Offline soldarTopic starter

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Re: Why/how do these LED lamps fail so fast?
« Reply #5 on: September 20, 2023, 08:07:47 pm »
Big Clive often autopsies (biopsies ? some aren't broken when he starts) LED lamps and looks into the current control. Often, there is a resistor whose value sets the LED current.

A while ago he investigated some Philips lamps only available in Dubai which were underrun for longer life. So he often explains how a given lamp can be modified to run at lower current.
I remember those videos.

When a previous lamp failed I did a bit of reverse engineering with the PSU, maybe hoping I could find some use for it but I remember (1) it was not isolated from the mains and (2) it was constant current with about 240 mA so I thought it really was not very useful. I will investigate furter to see if it can be modified but, in any case, if it is constant current then I can just put a resistor in parallel with the LEDs and it will shunt some current away.
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Offline IanB

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Re: Why/how do these LED lamps fail so fast?
« Reply #6 on: September 20, 2023, 08:19:40 pm »
You could:
- buy more expensive lamps (no guarantee of course, but cheap lamps are more likely to cut corners)
- buy lamps with more LED chips for a given light output (more chips means less power per chip)
- modify the lamp for lower power consumption by changing the current sense resistor (not practical for more than the occasional lamp)
- buy dimmable lamps and run them on a dimmer at lower power

I tend to use the last option, since for ambient light I do not need arc lamps. If I want bright task lighting, I just turn the dimmer up temporarily, or use a separate task lamp.
 

Offline srb1954

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Re: Why/how do these LED lamps fail so fast?
« Reply #7 on: September 20, 2023, 08:31:25 pm »
I saw electrolytics causing the trouble many times. Usually, the simple plastic encased bulbs. So my working theory is overheating, caps blowing up or getting leaky and cascading into semiconductor and LED failure.
In the many autopsies I have performed on failed LED lamps I find the electrolytics are never faulty and usually test as good as new.

The failures I find are always an individual LED having small burn marks in the centre; what BigClive calls the "black spot of death".
 
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Offline Zero999

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Re: Why/how do these LED lamps fail so fast?
« Reply #8 on: September 20, 2023, 08:37:26 pm »
I saw electrolytics causing the trouble many times. Usually, the simple plastic encased bulbs. So my working theory is overheating, caps blowing up or getting leaky and cascading into semiconductor and LED failure.
In the many autopsies I have performed on failed LED lamps I find the electrolytics are never faulty and usually test as good as new.

The failures I find are always an individual LED having small burn marks in the centre; what BigClive calls the "black spot of death".
I've seen both, but I sometimes it's the LED failing which caused the electrolytic capacitor to blow up. If the capacitor is across the LED, which is driven from a capacitive dropper and it's not rated to the full peak mains voltage, it'll blow, if the LED goes open circuit.
 

Offline soldarTopic starter

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Re: Why/how do these LED lamps fail so fast?
« Reply #9 on: September 20, 2023, 09:48:07 pm »
You could:
- buy more expensive lamps (no guarantee of course, but cheap lamps are more likely to cut corners)
- buy lamps with more LED chips for a given light output (more chips means less power per chip)
- modify the lamp for lower power consumption by changing the current sense resistor (not practical for more than the occasional lamp)
- buy dimmable lamps and run them on a dimmer at lower power

I tend to use the last option, since for ambient light I do not need arc lamps. If I want bright task lighting, I just turn the dimmer up temporarily, or use a separate task lamp.

I have not had good luck with dimmables. I bought a load of them at Ikea and they are complete crap. They sort of work (with a triac dimmer) in the brighter range but with more dimming they start to flicker. Utter crap.

OTOH, I have discovered that the "non-dimmable" types can be dimmed very easilly and effectively by simply putting a resistor or potentiometer in series. This woks better than buying the dimmable type. I have several desktop lamps with this kind of dimmer and they work very well. But I cannot see how to do it for a ceiling fixture controlled by a wall switch.

These ceiling fixtures that are failing I bought at a Big Box Depot.  It's not like I bought them at the Dollar Store.
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Online themadhippy

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Re: Why/how do these LED lamps fail so fast?
« Reply #10 on: September 20, 2023, 10:55:21 pm »
Quote
simply putting a resistor or potentiometer in series.
on AC a capacitor is a better option
Quote
But I cannot see how to do it for a ceiling fixture controlled by a wall switch
If you can live with 1 or 2 fixed levels change the single gang switch for a 2 or 3  gang  2 way switch  and wire the caps in the back of the switch.
 

Offline IanB

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Re: Why/how do these LED lamps fail so fast?
« Reply #11 on: September 20, 2023, 11:42:02 pm »
I have not had good luck with dimmables. I bought a load of them at Ikea and they are complete crap. They sort of work (with a triac dimmer) in the brighter range but with more dimming they start to flicker. Utter crap.

This seems to depend on the brand. I am getting really good results with Philips bulbs and a Lutron trailing edge dimmer (the Philips bulbs being the most important part of the equation).


 
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Offline shakalnokturn

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Re: Why/how do these LED lamps fail so fast?
« Reply #12 on: September 21, 2023, 01:08:04 am »
"The black spot of death" that could be caused by overcurrent (including overshoot at power up if PS is poor design), excessive heat or just inevitable thermal cycling.
The odds are that the bonding wire breaks away from the die slightly, the PS being constant current, when supplying an open string will hit its voltage limit often high enough for the open LED to arc, causing the whole string to flicker.

LED bulbs are definitely not what they're advertised to be, on average they're junk! (Once procuction, lifetime and recycling are taken into account I'd bet they're less ecological than your old tungsten filament...)
Osram in my experience have been expensive crap. I have had decent results with Philips and Toshiba though.
 

Offline alligatorblues

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Re: Why/how do these LED lamps fail so fast?
« Reply #13 on: September 21, 2023, 01:21:47 am »
If LEDs are run off constant current, the voltage remains steady. But if the current is not well controlled, the voltage will rise exponentially in comparison to the rise in current. It sounds like a poor design. The current creeps up. I doubt if it's worth trying to salvage.
 

Offline dobsonr741

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Re: Why/how do these LED lamps fail so fast?
« Reply #14 on: September 21, 2023, 01:33:18 am »
+1 for Philips. I’m only buying 458430.
 

Offline IanB

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Re: Why/how do these LED lamps fail so fast?
« Reply #15 on: September 21, 2023, 01:37:17 am »
If LEDs are run off constant current, the voltage remains steady. But if the current is not well controlled, the voltage will rise exponentially in comparison to the rise in current. It sounds like a poor design. The current creeps up. I doubt if it's worth trying to salvage.

Actually, this is not entirely true. Constant current supplies like to kill loads connected to them, and they are more deadly when the current is controlled more tightly.

Here's an experiment I did:

I took a length of nichrome resistance wire and connected it to a variable power supply with voltage regulation ("constant voltage"). I was able to gradually turn up the voltage until the wire glowed red, orange, yellow, quite brightly. Everything behaved fine.

Then I took the same length of wire and switched the power supply to current regulation ("constant current"). This time, when I gradually turned up the current the wire glowed red, started to be orange, and then quickly burned out and failed with a molten hotspot.

I tried again, two more times, with a fresh piece of wire each time. Each time the wire rapidly melted and failed before getting much beyond a dull red heat.

This is the problem with constant current supplies. They are really unforgiving and like to destroy the things they are powering.
 

Offline T3sl4co1l

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Re: Why/how do these LED lamps fail so fast?
« Reply #16 on: September 21, 2023, 02:44:32 am »
If LEDs are run off constant current, the voltage remains steady. But if the current is not well controlled, the voltage will rise exponentially in comparison to the rise in current. It sounds like a poor design. The current creeps up. I doubt if it's worth trying to salvage.

Actually, this is not entirely true. Constant current supplies like to kill loads connected to them, and they are more deadly when the current is controlled more tightly.

Here's an experiment I did:

I took a length of nichrome resistance wire and connected it to a variable power supply with voltage regulation ("constant voltage"). I was able to gradually turn up the voltage until the wire glowed red, orange, yellow, quite brightly. Everything behaved fine.

Then I took the same length of wire and switched the power supply to current regulation ("constant current"). This time, when I gradually turned up the current the wire glowed red, started to be orange, and then quickly burned out and failed with a molten hotspot.

I tried again, two more times, with a fresh piece of wire each time. Each time the wire rapidly melted and failed before getting much beyond a dull red heat.

This is the problem with constant current supplies. They are really unforgiving and like to destroy the things they are powering.

Actually, this is not entirely true.  Constant voltage supplies love to kill loads connected to them, and they are more deadly when the voltage is controlled more tightly.

Here's an experiment I did:

I took a string of LEDs and connected it to a variable power supply with current regulation ("constant current"). I was able to gradually turn up the current until the LEDs glowed painfully bright.  They got warm and that was about it.

Then I took the same string of LEDs and switched the power supply to voltage regulation ("constant voltage").  This time, when I gradually turned up the voltage, the LEDs glowed dimly at first, but as they started to heat up, they got brighter and brighter, until suddenly eclipsing the previous test and then nothing.  I tested the LEDs and found one had failed open.

I tried again, two more times, with parallel arrays of rectifier diodes this time, hoping that their robust ratings would do better.  The LEDs were only rated a few hundred mA after all.  Alas, each time, one of the diodes failed shorted, while the rest hardly even warmed up (WTF!).

This is the problem with constant voltage supplies. They are really unforgiving and like to destroy the things they are powering.

:)

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Offline T3sl4co1l

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Re: Why/how do these LED lamps fail so fast?
« Reply #17 on: September 21, 2023, 03:08:05 am »
Anyway, regarding LEDs: they are extremely long lived, in and of themselves, when ratings are respected.

The phosphor is actually the higher wear element, as it tends to fade over time.  The power density on it is quite impressive, for just a powdered mixture of ceramics that have this one magical property (fluorescence).  The blue LED chip itself also declines, but slower.

But that's just the LEDs themselves.

What's powering them, is another matter.

Lifetime can always be lower, and when it is economical to do so, it absolutely will be done.  Electrolytic capacitors are the most obvious and worst offender, with 2khr 85°C parts being common picks.  Put that in a stuffy lamp fixture and it might last mere months!

To make a long life LED lamp, one must use:
- Quality LEDs, derated modestly to reduce phosphor and LED chip wear
- A robust controller/driver, to limit current, typically to smooth light output, and optionally to perform power factor correction
- Long life or low-wear components (e.g. 5khr+ 105°C electrolytics, if any)
- Adequate transient protection and filtering (suitably sized MOV, somewhat-thicker-metallized EMI caps)
- VERY GOOD thermal management, spreading heat from the LEDs throughout the package, and allowing air to permeate it
- This includes the fixture, which should preferably be an open vertical or horizontal design, or made with holes or louvers in the reflectors/diffusers to allow free air flow.

For pretty much everything, heat is the killer.  Phosphors, despite being mere ceramics, are indeed sensitive to temperature, and seriously degraded when ran hot.  LED chips accumulate defects faster when hot, and when ran at high current density, as well.  Electrolytics notoriously degrade quickly when hot.  So do other capacitors, and other components generally.  Resistors, film capacitors, and semiconductors (other than LEDs), generally are fine within ratings of course, and those listed above are the major wear elements.  Filtering and transient protection are key to long life through environmental disturbances, especially surge which will progressively (or outright) damage passive / unfiltered / bare LED strings (and most likely filtered ones too, since the filter capacitor will only be 10s of uF, not enough -- nor nearly low enough ESR -- to swamp the pulse).

LED derating also has the knock-on benefit of lowered resistive losses (higher efficiency).  On top of this, for a variety of reasons, modern LEDs are closer to 3.0V drop at typical operating levels -- they're very efficient.  Compare to the oldest (~first generation illumination) which were typically 3.6V or more, and dissipated more like 90% of power input (which was still an impressive showing, as illumination technology goes).  The optical (quantum) efficiency is remarkable: modern LEDs produce so much light that the power dissipation is, not just palpably, but substantially, lower than the power input.  Compare a first-generation 100lm LED (might be an 8mm dia. package rated 3W), running near ratings, to a modern one at the same intensity (which might be a 3x3mm DFN, rated for, actually about 3W still, PCB permitting), dissipating under 1W!

Now, of a marketed product, obviously you can only establish so many of these things, even as an engineer willing to (potentially) destroy a few lamps in the process of evaluating them.  As a consumer, you only have whatever claims the manufacturer makes, and 3rd-party testing.  Some of the above points can still be evaluated, at least to a rough degree, as well as other points made in the posts above.  As far as temperature, besides fixture selection (that's your own responsibility as decorator!), large size (more dissipating area) and more open structure (same!) for a given power rating is a potential indicator of performance.

Also, regarding Philips specifically -- they made a remarkable early lamp, with I think still quite impressive lifetime today (though I think it's long since discontinued, I haven't checked?).  The trick was making a large, replaceable phosphor module to place on top of the LED chips -- thus running cool, giving diffuse emission, and addressing one of the primary concerns at the time.  Since then, phosphor lifetime has improved, as well as overall efficiency, and overall cost most dramatically -- this was back when LEDs were very new and rather pricey, IIRC, so the maintenance option had some promise.  Whether that was an acceptable compromise for consumers, or just a good trick to convince them to buy the things, I don't know, but, I guess it's funny that it was a losing proposition in the long run -- in that, LEDs are now so pervasive and cheap that such steps are irrelevant, the whole bulb is easily disposable.

(Which, let me see here.  Here's a press release about them:
https://www.ledsmagazine.com/company-newsfeed/article/16691970/philips-unveils-worlds-first-led-replacement-for-most-common-household-light-bulb
Teardown: https://youtu.be/b4ZBfmLGRrk
MSRP about $50: https://www.led-resource.com/2012/09/philips-l-prize-award-winning-led-bulb-review/
I don't see an article about when they were discontinued, maybe it only lasted a few years even. Well made unit for what it is, just not very competitive!)

You can also choose just completely different designs that literally never existed before.  Well, sorta kinda.  Fluorescent tubes are linear sources, obviously, and glow discharge systems have existed before, but tubes are rather rigid, and glow discharge requires custom glassware.  LED strips can be placed anywhere, easily, and trimmed to length (with minor restrictions).  They do need to be wired up correctly, but once installed, they are distributed sources, that run cool, while giving diffuse wide illumination.  Combined with color customization options, whole new design/decoration spaces are possible.
« Last Edit: September 21, 2023, 03:31:57 am by T3sl4co1l »
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Offline soldarTopic starter

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Re: Why/how do these LED lamps fail so fast?
« Reply #18 on: September 21, 2023, 11:54:53 am »
This seems to depend on the brand. I am getting really good results with Philips bulbs and a Lutron trailing edge dimmer (the Philips bulbs being the most important part of the equation).

Thanks for that link. The video is very interesting and informative and I will keep that information in mind.

The thing is that I am replacing ceiling fixtures, not lightbulbs. I will have to see if Philips makes similar fixtures.
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Online themadhippy

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Re: Why/how do these LED lamps fail so fast?
« Reply #19 on: September 21, 2023, 12:56:44 pm »
Quote
The thing is that I am replacing ceiling fixtures

Quote
And what ticks me off is that these are complete ceiling fixtures where you can't just change the light-bulb like in the good old days.

why are you repeating your mistake, replace the fittings with something that has a standard lamp base
 

Offline Zero999

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Re: Why/how do these LED lamps fail so fast?
« Reply #20 on: September 21, 2023, 01:49:50 pm »
Actually, this is not entirely true. Constant current supplies like to kill loads connected to them, and they are more deadly when the current is controlled more tightly.

Here's an experiment I did:

I took a length of nichrome resistance wire and connected it to a variable power supply with voltage regulation ("constant voltage"). I was able to gradually turn up the voltage until the wire glowed red, orange, yellow, quite brightly. Everything behaved fine.

Then I took the same length of wire and switched the power supply to current regulation ("constant current"). This time, when I gradually turned up the current the wire glowed red, started to be orange, and then quickly burned out and failed with a molten hotspot.


Actually, this is not entirely true.  Constant voltage supplies love to kill loads connected to them, and they are more deadly when the voltage is controlled more tightly.

Here's an experiment I did:

I took a string of LEDs and connected it to a variable power supply with current regulation ("constant current"). I was able to gradually turn up the current until the LEDs glowed painfully bright.  They got warm and that was about it.

Then I took the same string of LEDs and switched the power supply to voltage regulation ("constant voltage").  This time, when I gradually turned up the voltage, the LEDs glowed dimly at first, but as they started to heat up, they got brighter and brighter, until suddenly eclipsing the previous test and then nothing.  I tested the LEDs and found one had failed open.
Both statements are correct, but it depends on the load. If it has a positive voltage vs temperature coefficient, like a piece of nichrome wire, then it will be more likely to be killed by a constant current supply, whist if it has a negative voltage corefficient, such as an LED, it will be more vulnerable to a constant voltage power supply. As the nichrome wire heats up, its resistance will increase, but the currrent is constant, so the supply will increase the voltage leading to progressively more power dissipation. As the LED heats up, its foward voltage will reduce, for the same current, but the power supply will maintain the same voltage, so the current will increase, leading to increasingly highr power dissipation. The nichrome wire heater should be powered from a CV power supply, whilst the LED off a CC power supply.

« Last Edit: September 24, 2023, 08:14:23 pm by Zero999 »
 
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Offline David Hess

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Re: Why/how do these LED lamps fail so fast?
« Reply #21 on: September 21, 2023, 01:56:01 pm »
Anyway, regarding LEDs: they are extremely long lived, in and of themselves, when ratings are respected.

The phosphor is actually the higher wear element, as it tends to fade over time.  The power density on it is quite impressive, for just a powdered mixture of ceramics that have this one magical property (fluorescence).  The blue LED chip itself also declines, but slower.

But that's just the LEDs themselves.

What's powering them, is another matter.

Lifetime can always be lower, and when it is economical to do so, it absolutely will be done.  Electrolytic capacitors are the most obvious and worst offender, with 2khr 85°C parts being common picks.  Put that in a stuffy lamp fixture and it might last mere months!

Exactly, the "50,000 hour operating life" specification is a fantasy based on the operating life of the LEDs to reach 50% brightness and has nothing to do with operating life and reliability of the LEDs and ballast.

When California passed their LED bulb mandate, they based the economics on that 50,000 hour operating life saying that LED bulbs would actually cost less over the long term.  (1)  After a few years, they admitted in a report that that operating life was grossly exaggerated (I knew that) and that the economics were so bad that incandescent bulbs were better; the extra cost of the LED bulbs was greater than the extra cost of the power for an incandescent bulb.  (2) Unfortunately, but not surprisingly, California has since censored that report and removed access to it, because fuck you citizens.

A reliable electronic ballast needs to not use operating life limited parts like aluminum electrolytic capacitors, be significantly derated, and include protection circuits which themselves will not fail.  Because of operating temperature, it probably also needs to use hybrid construction.

(1) I do not believe that politicians are stupid enough to fall for this.  They did it deliberately for purposes of rent seeking, so fuck them.

(2) I have had the same experience with government mandated electronically commuted motors which replace less efficient shaded pole motors.  Their operating life is short and replacement cost is high so their total cost of ownership is higher despite the power saved.
 

Offline soldarTopic starter

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Re: Why/how do these LED lamps fail so fast?
« Reply #22 on: September 23, 2023, 09:47:23 pm »
OK, I have had a closer look and the circular strip of leds is composed of 102 discrete units which may have more than one led per unit. I do not know how they are connected. 

Three contiguous leds are blackened and, sure enough, they remain dark when the others light.

Anyone know how they might be connected? If I know this maybe I can try a repair by taking them out of circuit or by shorting them or by substituting a resistor....
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Offline coppice

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Re: Why/how do these LED lamps fail so fast?
« Reply #23 on: September 23, 2023, 09:57:35 pm »
Anyway, regarding LEDs: they are extremely long lived, in and of themselves, when ratings are respected.
Some are. Some aren't. There used to be a huge number of LED lamps that gradually dimmed to a level of uselessness over a year or two. That problem seems to have improved a lot, but some still rapidly dim.
 

Offline Zero999

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Re: Why/how do these LED lamps fail so fast?
« Reply #24 on: September 24, 2023, 09:19:34 am »
Have you measured the voltage across the LEDs which do work?
« Last Edit: September 24, 2023, 09:52:23 am by Zero999 »
 


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