MTBF, MTTR, and MTTF for electronic equipment

[elwali]

Hi All,

Wondering how to measure (or calculate) reliability factors (MTBF, MTTR, and MTTF) for a device? let's say a cellphone or laptop. I'm pretty sure individual components have their reliability factors measured by manufacturers.
but a gain how can we be sure that a device will work for 10 or 20 years non stop?! I wonder what NASA guys do 

[rfeecs]

Usually for a system a reliability prediction is calculated, using MIL-HDBK-217 or other similar method.

For individual components, the manufacturer provides MTTF data.  This data is done by accelerated stress testing.  For example testing at elevated temperatures until failure.

[Kjelt]

Products can also be stress tested, this works with statistical models, like how many products should be tested, can be 10,50,100 etc. and then put working in high humidity, high temperature and other stress factor environment. Than every x hours track how many devices have failed and that will result in some benchmark statistic for that product.
For instance for ledlamps there is something like this a figure of L90B50 25000 means that after 25000 hours , 50% of the lamps still have 90% of their initial lumens.
Now how you define your MTBF is another thing because when do you think your lamp fails? When it breaks or has 0 lumens (can take centuries)? If it has 10% lumens?