On Tue, 1 Nov 2016 02:38:46 +0000 (UTC), Algeria Horan
wrote:

You would bring up *more* complex LED-lifetime terms to figure out!

I should have guessed it was you. I like to explain how things work,
without offering a judgment or opinion. This type of question really
belongs in Candlepower Forums.

And, you would also find MARKETING BULL**** in the mix!

It happens. I have some marketeering experience somewhere on my
resume. 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

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

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. 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.

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. 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.
"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)

Well, I was sick of replacing very expensive non-standard Philips
fluorescent bulbs, so I bought the LED light fixture from Costco just to get
rid of the non-standard wacko shaped bulbs that kept burning out anyway.
http://uk.rs-online.com/web/p/non-in...lamps/4075597/

600lumens / 9watts = 67 lumens/watt. Barf.
Philips claims 200 lumens/watt and Cree claims 300 lumens/watt:
http://www.philips.com/consumerfiles/newscenter/main/design/resources/pdf/Inside-Innovation-Backgrounder-Lumens-per-Watt.pdf
http://www.cree.com/News-and-Events/Cree-News/Press-Releases/2014/March/300LPW-LED-barrier
You may not see that at Costco for a while, but maybe if Philips and
others get back into the LED biz.
http://www.memoori.com/samsung-joins-philips-siemens-in-led-lighting-exodus/
It's not too obvious, but both claims assume that the LED is cooled to
approximately room temperature.

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.
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.

I'm guessing the LED light fixture I bought lasts no longer than a couple
sets of incandescent bulbs would have.

Talk to me in 30,000 hrs and we'll compare notes.

Time will tell.

You have a talking clock?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558