LED Bulb dying

This is just nuts. You can't get any meaningful MTBF by the method you just described. What you showed was taking 1000 bulbs and testing them for just an hour. That isn't predictive of MTBF over the life of the bulbs. Following that method with say an ordinary incandescent, you'd come away with the impression that they hardly every fail at all, because incandescents rarely fail in the first hour and it has little to do with how long they last in service. (In reality what you'd be measuring is the infant mortality by your 1 hour method)

You find MTBF by testing the devices continuously over many hours, finding out how many fail at 100 hours, 1000 hours, 10,000 hours and then determining on average how many hours you get before failure. Ed has it right, MTBF, properly calculated, is the average number of hours that you get from an LED before it fails. In your bulb example, you only tested one bulb to the failure point, in essence you have a sample size of one.

"MBTF does not tell you anything about the second and so forth hours."

Of course it does. If we know that a bulb or an engine has an MTBF of 20,000 hours, then we know that on average, that's how many hours they go between failures. The device is very unlikely to fail at two hours, or two hundred hours, but has a high failure rate at 20,000 hours. Are you telling us that MTBF only tells you about the first hour?

That's scary. And if that's the case, why is it that every time you've used the term here, you keep posting "MBTF", when it's actually MTBF?

That is why I do not like to buy through the mail. Within 90 days, I expect a local dealer to replace or refund a defective item.

With regard to LED Bulb reliability, why should it be much different from CFL Bulbs? I have taken some defective CFL Bulbs apart and found the defect is mostly due to an electronic part failure. Often they do not they last long enough for the Fluorescent tube to turn black from use.

Fred

MOST home warrantees are a total expense -you'd have to buy a realshack for it to ever pay off - and even then the exclusions would end up killing you. Extended warrantees on complex home electronics MAY be worthwhile - particularly if they also cover accidental damage or loss.

Tool warrantees on tools you buy locally and get coverage at point of sale can be worthwhile - particularly when they are a universal warranty. Snap-on warrants their hand tools - replace "at the truck" Craftsman warrantee was at any sears store. Mastercraft pro tools - any Canadian Tire store, Proto at any UAP, etc.

Most of the tool warrantees that I have seen are already factored in the price of the tool from the more expensive brands. YOu do not have the option of one or not. That is if I go to Sears and get a Craftsman wrench it will cost a certain price and I can not opt out of the warrantee to get for a lesser price. If I buy an oven from them, they will try to sell me an extended warrantee. I do have a choice on that.

I'm glad somebody noticed. The 'mean' time of a single failure is exactly the time of that failure and is basically useless as a measure.

I would think that they could test 100 items until maybe 25 of them failed and get the mean time from that selection of failures.

You also have the choise whether you want to pay the extra for the craftsman or buy the Sears brand with no warrantee.

Most places sell the "good stuff" with a warrantee and the "cheap crap" without.. Some of the "cheap crap" isn't even all that bad, but you are taking the chance - if it breaks you buy another one.

Its also called a pontoon bridge. Anyone who it not dim knows that.

A full wave bridge is necessary to keep LEDs above bigger waves.

LEDs work best when a constant current source is beneath that bridge. Current must be constant and only in one direction (always a DC or downstream current).

That would be getting closer to the real number, but even that gives you an MTBF number that is too low. That's because you're only counting the 25 that failed and not counting the 75 that were still working OK. You know the MTBF based on averaging the number of hours it took for those 25 to fail is a lower number than what you would calculate based on averaging what you'd get from all 100. Knowing something about the physics of whatever the system is, eg that it would typically follow a bathtub shape curve, you could use some statistical methods to generate a better estimate of the real MTBF based on the results of just 25 failing out of 100 and stopping the test at that point.

Yet, you can't even spell the acronym correctly.

MTBF - Mean Time Between Failures

"The predicted elapsed time betwen inherent failures of a system during operation".

Of course, in a system that can't be repaired, such as an LED A19 bulb, the proper acronym is MTTF (Mean Time To Failure).

Note that it is incorrect to extrapolate MTBF to give an estimate of the life time of a component, because of the much higher failure rate during end-of-life.

Note also the first term is 'Mean', which implies failures on either side of the computed MTBF can be expected.

Actually the highest failure rate per unit time is when the product is new. "infant mortality" is a bigger issue than "old age".

I guess technically you are mabee correct, because just before they fail - at whatever age, they are "approachiung end-of-life"

Predicting "end of life" becomes the issue. We had all kinds of trouble with LED MR16 or GU10 (whichever the 12 volt ones are) so we went back to halogens - these are in a 14-20 foot mceiling. They have been in a month now, and already 3 out of 54? are dead.......

If that were true, then there would be a huge scrap bucket at the factory, with most of the product coming off the line failing. Sure there is a higher failure rate in infancy than in the middle of life, but the highest failure rate is at the end of life when they are almost all failing.

IDK what the difference here is between technically correct and just correct.

All I know is LEDs can't take heat. Halogen bulbs can. Maybe it is hot up there?

Don.

It's a bit warmer up there than at floor level but that doesnt explain why the halogens are letting go even more quickly than the LEDs did - - -

because heat rises, and halogens create a lot more of it, particularly base-up.

Just lost a 4th halogen this morning - - -

I was replying to "All I know is LEDs can't take heat. Halogen bulbs can. " -- and noting the halogens are dropping like flies - even moreso than the terrible results we had with LEDs.

Life expectancy of a halogen in normal service is determined by filament temperature (ie voltage) and hours of operation. Monitor for high voltage or voltage variations that cause intensity to change. If on a properly wired circuit, that bulb should not change intensity even as other major appliances power cycle.

An abnormal event is, for example, traffic on a floor above that bulb. Incandescent bulbs fail pre-maturely with vibrations only when hot (powered).

Vince Foster posted for all of us...

I was going to post a reply like this but too lazy to figure out how many hours in the year. The bulb probably didn't have a longevity on the package so it means FOREVER in his mind.