Rod Speed ha escrito:


Please explain how the manufacturer of a light bulb, fluorescent
lamp or CFL can provide an estimate of the lifetime of the lamp.

That is trivial to do by running an adequate sized batch of
incandescent light bulbs under appropriate test conditions etc.

Don´t say "They can´t because it´s impossible".
Explain exactly why it´s impossible.

Its up to those who claim that its possible to design a device
to die one year after the warrant expires how that can be done.


Well, it can be estimated how long will a power semiconductor run if
you leave it without a proper heatsink. Open any Samsung TV, for
instance, to see for yourself how important transistors are left bare,
dissipatting heat to the air. I don´t see why it should be difficult
for the manufacturer to know that these particular transistors left
overheating will fail within a finite number of hours. Also, you will
notice that the same circuit will have electrolytic capacitors near
heat sources, when it´s a well known fact that heat shortens
dramatically the life of electrolytics caps. The manufacturer know how
to properly design an electronic circuit in order to provide a long
life, but it also it knows how to design it to fail within a short term
under certain conditions, and accordingly they estimate a warranty just
long enough to cover the product for a safe term, a safe term for the
manufacturer, not the user.

Of course it´s impossible to predict exactly how many years the TV
will last, but the manufacturer count with statistical data which says,
for instance, that a TV set is turned on 10 hours per day for instance,
and taking that into account, and estimating how long the weakest part
of the TV will last under these conditions, they can determine the
warranty lapse.


The quote the useful lifetime of a hardrive in MTBF hours.

That is calculated, not measured. Convert that MTBF
to years and you will discover why they cant possibility
have tested them to get those numbers.

Don´t answer "it´s impossible" if you are not prepared to give
a real explanation. Samsung, Seagate, WD... any decent hard
drive manufactures gives an estimate lifetime of their products.
These estimates are provided in the datasheet of each harddrive.

And they are ESTIMATES, not measured results.

Exactly, these are estimates, and most of the time very accurate,
specially those concerning the maximum number of startups/stops the
drive can tolerate before the heads get completely worn.

I don´t want to imply that all manufacturers are dishonest per se, but
I can easily see how a given manufacturer can produce different items,
with differents level of quality of design and manufacture. And these
differences *will* impact the useful lifetime of the final product.