LED Bulb dying

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On Sun, 11 Sep 2016 13:53:00 -0400, Ralph Mowery

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.
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On Saturday, September 10, 2016 at 11:44:04 PM UTC-4, snipped-for-privacy@snyder.on.ca wrote: ..snip...

Jumping in late here as I hadn't been following this thread.
Please explain your math. You spent $18 to replace the module that is now on the shelf. You spend $22 on the module that is in the laptop.
If the one of the shelf effectively cost you $40, then wasn't the one in the laptop effectively free?
It seems like it was going to cost you *something* to get your laptop up and running (either $18 or $22), so why do feel that the total amount that you spent is sitting on the shelf?
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On Tuesday, September 20, 2016 at 4:06:35 PM UTC-4, DerbyDad03 wrote:

Inquiring minds have to wonder how it could cost $18 to ship a memory module for a laptop? I just shipped a box that's 26x9x8 that weighs 6 lbs from NJ to CA via Fed Ex economy ground for $13. A memory module should cost less than $5 to ship.
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On Tuesday, September 20, 2016 at 5:24:43 PM UTC-4, trader_4 wrote:

I'm thinking Canada to California, electronics, customs, etc.
I could be wrong, just my thoughts.
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On Tue, 20 Sep 2016 16:31:55 -0700 (PDT), DerbyDad03

almost double that for 2 day, and even more for "next day"
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On Tue, 20 Sep 2016 13:06:31 -0700 (PDT), DerbyDad03

If I had a "better brand" lifetime warranted module it would not have cost me anything to get it replaced - just take it back to the supplier and walk out with a new one.
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snipped-for-privacy@snyder.on.ca;3626698 Wrote: > If I had a "better brand" lifetime warranted module it would not have > cost me anything to get it replaced - just take it back to the supplier > and walk out with a new one.
Best warranties are often found on least reliable products. With numerous fine print exemptions. There is no replacement for spec numbers that actually claim it does what it is suppose to do.
--
westom


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On Tuesday, September 20, 2016 at 9:34:45 PM UTC-4, snipped-for-privacy@snyder.on.ca wrote:

But you didn't have a ""better brand" lifetime warranted module". You had what you had. Why bring hypotheticals into this?
The module on the shelf cost you $18, not $40. The one in the laptop cost you $22.
Regardless of how *you* want to do the math, you either wasted $22 by being impatient or you wasted $18 "just on principal". Either way, the one on the shelf did *not* cost you $40.
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On Saturday, September 10, 2016 at 10:17:50 PM UTC-4, T wrote:

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?
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trader_4 pretended :

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.
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On Sunday, September 11, 2016 at 2:14:50 PM UTC-4, FromTheRafters wrote:

+1

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.
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On 09/11/2016 11:14 AM, FromTheRafters wrote:
Yup. The already do that. It is called the "bath tub curve". More at Wikipedia:
https://en.wikipedia.org/wiki/Bathtub_curve
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.
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T explained :

The name pretty much says it all, but like many other things, applying it outside of its intended range gives erroneous results.
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On 09/14/2016 06:24 PM, FromTheRafters wrote:

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.
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On 09/14/2016 10:00 PM, T wrote:

Fact: Manufacturers use acronyms to confuse and deceive people.
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On 09/15/2016 02:04 AM, GOWGN wrote:

Ha! I can tell you don't work for marketing! :-)
There is no end to the bull shite that marketing smothers us in a constant basis.
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On 09/15/2016 06:34 PM, T wrote:

In my opinion, Shop-Vac fudges the specs a bit.
https://www.shopvacstore.com/the-shop-vac-16-gallon-6-0-peak-hp-wet---dry-vacuum-with-built-in-water-pump-details.aspx
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.
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On Wednesday, September 14, 2016 at 6:00:50 PM UTC-4, T wrote:

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
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On Sunday, September 11, 2016 at 10:56:46 AM UTC-5, trader_4 wrote:

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On 09/16/2016 07:26 PM, snipped-for-privacy@hotmail.com wrote:

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
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