On Tue, 01 Nov 2016 09:02:59 -0700, Jeff Liebermann wrote:

I should have guessed it was you.

Yeah, it's me.
My friends joke I'm half the Internet alone.

I'm always solving problems, asking questions, delving deeper, etc., as are
you (but you don't like to admit it).

I like to explain how things work,
without offering a judgment or opinion.

You have always been balanced, ever since I learned from you how to set up
my WiFi rooftop antenna on a.i.w years ago, when you still frequented that
forum (before you absconded to s.e.r that is).

And, you would also find MARKETING BULL**** in the mix!
It happens. I have some marketeering experience somewhere on my
resume.

Me too, truth be told (but I try to hide my curricum vitae far more so than
you do).

When I was in Marketing, we made hay with any advantage we could, and we
swept under the rug all the disadvantages. Plus we said things like "better"
and "new" and "more" since they couldn't be easily disputed.

Basically, we took whatever it was that the engineers gave us, and we
marketed the **** out of it, so that it *looked* like gold in the
literature.

But it was no different than anything else was.
Every good thing had a bad downside to it.

Like everything on this planet does.

Speaking of bull****:
"How LED Lighting May Compromise Your Health"
http://articles.mercola.com/sites/articles/archive/2016/10/23/near-infrared-led-lighting.aspx

OMG. I'm losing out on all that healthy infrared radiation!
And that EMF is the "leading cause of blindness" in the USA!
Quick. Gimme one of those famous infrared saunas in Santa Cruz hippytown!



LM-80 = a standard for measuring LED lumen maintenance & depreciation
LM-40 = time for 50% of the lamps in a large group to burn out
L70 = time to degrade to 70% of its original lumens
L80 = time to degrade to 80% of its original lumens
L90 = time to degrade to 90% of its original lumens
Reported TM-21 = predicts lifetime using LM80 + optimistic magic math
Calculated TM-21 = predicts lifetime using LM80 + more optimistic magic math

Nice summary. Sounds about right.

Thanks for noticing. I generally read all your references.
If you are gonna go to the trouble to reference them in a thread I authored,
I'm gonna go to the trouble to at least skim them (I read fast, very very
very fast, faster than most people can talk, and I type fast too, so it's
easy for me. When I was a kid, I was in a special reading program for the
gifted, where they had a machine that forced me to read faster and faster
and faster - dunno why my parents subjected me to that - but they did.)

I believe there are a few other
standards that I missed. Standards are a good thing. Every company
should have one.

I think the important point is that we each can pick the standard that makes
the most sense to us, but also, that information has to be readily available
to us.

I'm not sure yet, which is the readily available standard, but I'd prefer
the L70 myself, to be the standard that I get the information on.

Seems to me that the "LED lifetime" figure everyone is quoting in this
thread and in other threads is total bull****, so far...

Nope, because it's all we have to work with. Like I ranted, nobody
does 30,000 hr life tests. Therefore, nobody knows the "real world"
lifetime of an LED light.

At the moment, I'm guessing the one LED lamp I have will last no more than 4
or 5 years. (Call me up in 5 years and I'll let you know how it turned out.)

The best we can do is parametric testing,
accelerated life tests, and the usual guesswork. The first two are
quite valid and result in numbers that usually come fairly close to
reality. The guesswork, you can guess what I think.

Except that every once in a while, there will be failures in the drivers
that I don't think are being tested here. Are they?

It's much like MTBF (mean time between failure) which attempts to
estimate the life of a device based on historical tests and operating
conditions.

Understood.

These component estimates are conglomerated into a figure
for the device. However, the intent is not to estimate the lifetime,
but rather the number of expected failures in a population of LED's.

Makes sense.

"What Every LED Engineer Needs to Know About MTBF"
https://www.fairchildsemi.com.cn/Assets/zSystem/documents/collateral/whitepapers/LED-Lighting-MTBF-White-Paper.pdf
(Note: I haven't read through this yet)

The abstract mentions MTTF, which is essentially what I'm asking in this
thread, I believe, whereas MTBF is for repaired items (according to the
abstract).

It implies that we should use MTTF since we're gonna throw out the LED
fixture once it fails us.

That Fairchild paper goes into details (e.g., how to accelerate and what
happens if the failure rate is 0), but that's the net I take out of it by a
quick skim.

What irks me is that they seem to never have run into someone who doesn't
accept that bs as an "answer" to the question of how long the light fixture
is expected to last.

For good reason. From the point of view of the manufacturer and
vendor, the ideal product blows up 1 day after the warranty expires.

The funny thing is that there are so many stupids out there who talk about
"warranties" as if they're NOT purely marketing bull****!

On the car forums, I hear all the time people comparing batteries by their
warrantee, as if the warrantee conferred some magical quality on the
electrical and lifetime properties of the battery!

They even compare *tires* by warrantee! Geesuz.
It's sad how stupid people are, in general.
Very very sad.
Sigh.

I've ranted on the topic before, where simulation and modeling tools
are used to insure that multiple parts all fail just after some preset
time limit. My favorite example are GE(?) water heaters with 6, 9,
and 12 year warrantees, and roughly proportional pricing, but where
the only difference is the type and size of the anode rod. Details if
anyone wants them.

Interesting. Very interesting. I just had a water heater go, in fact, and,
um, I shouldn't say this, but I had never replaced the anode. All that was
left was some whitish stuff and the inner steel wire. The heater corroded in
7 years, but that was my fault for not replacing the anode (although it was
almost impossible to twist off, so, if you're gonna replace anodes, at least
crack the top hexnut every six months or so).