For LEDs, LM-80 data is used to extrapolate lifetime data via the TM-21-11 methodology. Its not great, but it is what we have. If you read the standard, it has pretty good summary of the drawbacks of the current approach to lifetime extrapolation:

https://www.ies.org/product/projecting-long-term-lumen-maint...

But, in practice, other components generally fail before the LEDs have a (binary) failure.

There are standardized tests for all this stuff, as you might imagine. One in this case would be the LM80 test.

Source: https://www.amazon.com/LED-Lighting-Primer-Future/dp/1449334...

Thanks. For the lazy... it's explained here:

https://www.eetimes.com/document.asp?doc_id=1280235