On Mon, 31 Oct 2016 15:13:01 -0700, Jeff Liebermann wrote:

Perhaps you might be interested in "lumen depreciation", L90, L80,
L70, TM-21, LM-80, LM-40, etc.
http://www.p-2.com/blog/lighting-basics-lifespan-lumen-depreciation-l70-tm-21-lm-80-lm-40-and-other-confusing-yet-useful-terms/

Yikes Jeff!

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

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

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

Few run 30,000 hr tests.

Hence the "magic math" on the lifetime figures...

The basic idea is to test the LED at various elevated temperatures,
connect the dots on a graph, and extrapolate to how long it might last
at some specified operating temperature. At 25C it will last nearly
forever, which assumes that the LED has some form of cooling system.
One can generate amazingly large and impressive numbers this way.
Despite my derisive comments, it does work quite well when performed
honestly and where the test parameters are sane.

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

I doubt if we will ever see detailed life test results from Costco
LED's as you might from higher priced LED luminaires.

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/

I asked Costco and the manufacturer to provide the information on the
lifetime of the LED light that I did buy.

I didn't get anything more than "hey, the warranty is 5 years so that's how
long it lasts".

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.

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

Time will tell.