LED Bulb dying

[clare]

ALL MR16 bulbs are rated for base up - it is almost the only way they are EVER used.

[clare]

Built as a commercial strip plaza, converted at time of construction to high end office space - 7 years old. Has never had incandescent lighting. Has some "U" shaped flourescents - have replaced, if memory serves me correctly, 3 of them There are some incandescents in washrooms and "accent lighting" as well as a Chandelier - I've replaced half of the bulbs excluding the chandelier, and quite a few in the chandelier - havesince relamped it with LEDs - have had a few failures, bur not a high rate They are base down. I don't have the brand of the halogens handy but they were purchaced from my normal electric supply house, Torbram Electric.

The fixtures are mounted in suspended ceiling, vented to the open space above (minimum 4 feet clearance to roof decking)

[T]

You got that! CFL's will last a log time too, but no one will spend the necessary money on one to achieve it.

White LED's are actually more fragile than you would think. You have to get the heat out or they lose their ability to shed light. Colored ones can take a lot more heat.

Hi Songbird,

I am an Electrical Engineer. You are not off track. You are following best practice in troubleshooting. Clare is just looking at what is most probable. There is just a tiny bit of cross talk here.

Basically, your advice was spot on. If a fresh bulb doesn't change the symptom, or trying the suspect bulb out on another wiring run and the bulb works properly, it is the wiring and could be a danger to the structure.

Now, back to my zucchini!

-T

[T]

Yup. The already do that. It is called the "bath tub curve". More at Wikipedia:

We studied it in college.

There is a common misconception that MTBF means how long it will last. It is pretty useless for determining longevity. Folks often mix up "Mean Time to Failure (MTTF)" with MTBF.

[T]

Actually they resemble each other. It is called the "bathtub curve". More at Wikipedia:

[T]

And "YOU" never make a typo? Oh pardon me!

Oh no you misspelled "between"! Oh My Gosh!!!! A TYPO, A TYPO, A TYPO !!! You must have gone to the same publik skool I went to! AAAAAAHHHHHHHH !!!!!

You also gave a superficial definition. The full definition is Mean time between failures (MTBF). The total functioning life of a population of an item divided by the total number of failures within the population during the measurement interval. The definition holds for time, cycles, miles, events, or other measures of life units. --DOD-HDBK-791, page 215

You missed the "measurement interval". It is one hour. I have done this professionally for the military. There is much more to it than the superficial definition you gave. And it does lead to a lot of misunderstandings, like yours. The general public does not realize the tables you use to look these things up (also published by the miliary) are all based on one hour. You are relying on the work of others to come up with your predictions. Intervals other than an hour would require all kinds of math manipulations to combine it with MTBF of other parts analyzed in your prediction. You are not just analyzing one part by itself, you can just look that up.

It is improper to interpolate Mean Time To Failure (MTTF) with with MTBF do to the way MTBF is calculated.

And, I do not mean to poke the condescending in the eye, but infant Mortality and Old Age Failure (Wear Out Failure) match each other (one is the inverse of the other). It is called the Bathtub curve.

Now you can go back happily condescending about all our typos, not yours, of course.

And yes, I had to study all the above shit.

[FromTheRafters]

The name pretty much says it all, but like many other things, applying it outside of its intended range gives erroneous results.

[T]

You would never believe how much sticking your finger in the wind is involved in MTBF predictions too.

If you want to know what the manufacturer really thinks, look at his warranty. On the above bathtub curve, we were taught in college to set the warranty at 90% of the useful lifespan.

[GOWGN]

Fact: Manufacturers use acronyms to confuse and deceive people.

[trader_4]

In the case of an LED light, which is what we are discussing, MTBF and MTTF are the same, because there is no repair. In a repairable system, where it's not scrapped at first failure, you can repair it, then continue to measure the time to the next failure. With an LED bulb the first failure is essentially the last

[trader_4]

It's sure odd that you made the same "typo" four times in a row in the same post and never once got it right. What are the odds of that?

What a buffoon. The measurement interval is exactly that, how long the system if being measured for failures. You have a jet engine being tested, you clock how long it is before a failure occurs. Typically it's measured in hours, but it's not "one hour", it as long as the test goes on, which is typically tens of thousands of hours. And your own reference says it can be measured in miles, cycles, etc. How does that translate to your "one hour"? So, even your own cite says you don't know what you're talking about.

I have

That's scary.

There is much more to

ROFL

Intervals other than an hour would require

So we can only test light bulbs, LEDs, jet engines for a measurement interval of one hour? Good grief

Sadly you didn't even learn the basics.

[T]

Ha! I can tell you don't work for marketing! :-)

There is no end to the bull s**te that marketing smothers us in a constant basis.

[FromTheRafters]

It's not really an acronym.

Use the MWBT (Mean Words Between Typos) formula [See Appendix E], just add up all of the words in intervals between the starting typo and between subsequent typos and divide by the number of typo events recorded excluding the starting typo. It comes to about 14.33 WPT (Words Per Typo) I think.

Be advised, small data sets may give suboptimum results and excluding the 'warm-up' period and the 'past bedtime' period is recommended for the best results.

Not just "how long the system if[sic] being measured for failures", but where. The idea is to exclude the outliers of 'infant failure' and 'system age wearout' by getting the data set from the steady rate of midlife operation from the nearly flat bottom of the bathtub curve.

It would certainly speed up the process, and marketing would just love the great looking numbers. No need to test them for *two* hours when you get such good results from one hour.

[Danny Jones]

In my opinion, Shop-Vac fudges the specs a bit.

They claim 6 peak horsepower yet their specs also state 120 Volts and 11.8 Amps.

So how does a 1416 watt motor yield 6HP? Last I knew, a 100% efficient motor would yield 1 HP at 746 watts so this Shop-Vac is actually less than 2 HP.

[T]

Hi Rafters,

I once asked how the military came up with the numbers. I don't remember exactly what I got back, but the term "Fudge Factor" had to apply. I do believe they did things like speed up aging by heating the guys and then used formulas to extrapolate the numbers back to room temperature. Different types of parts had different formulas. Iron versus silicon, for instance. Or something like that.

Here is a good example of where MTBF means nothing:

"Life Expectancy: 1.2 million hours Mean Time Between Failures (MTBF)"

Does anyone actually think that the average lifespan is

137 YEARS? Oh brother. The metal would corrode by then. The silicone in the transistors would start dripping and turning back into glass.

The real "Life Expectancy" would be the warranty, which is five years. And five years is good for such drives. But 137 years does sound a lot better to the marketing weasels.

-T

Hmmm. I wonder if I made any typos. AAAAAHHHHHHH !!!!

[FromTheRafters]

It's about using the right tool for the right job and not confusing mathematical predictions with actual empirical measurements.

Marketing can use engineering numbers to confuse and confound end users who think units were actually tested for 274 years on a test bench and half-life used as a conservative measure of life expectancy.

[T]

Criminy! They even have software for it now! I could have used that 30 years ago!

You got that.

My opinion, MTBF is only useful if you are comparing one MTBF number to another.

Thank you for the links,

-T

[RedAlt5]

That doesn't make sense either. When a company makes a new product do they test it for 5 years to get a true MTBF before they market it? No,they pick a good sounding one and hope it works that long.

[T]

Hi Red,

If I remember correctly when I use to do this for the military, the numbers we used were from tables where they cooked the parts to simulate aging. Then they did a formula on it to come up with an MTBF. Everything was based on one hour.

MTBF is really only useful if comparing one part's MTBF to another part's MTBF.

The warranty is where you get any real idea of how long the manufacturer thinks things will last.

-T

[Paintedcow]

I had another identical bulb in another part of the barn. That one was installed about the same time and was also left on all the time. That one is now dead too, except that one is completely dead. I tried it in another socket, DEAD !!!!

Interesting how both had about the same life span.....

I replaced both today with new LED bulbs (another brand).