system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can companies say their energy saving light bulbs will last 20 years?

How do they test them as i imagine they haven't been left on for 20 years as that would be impractical and they weren't invented that long ago. e.g. LED bulbs.
gpt
LED's have been around since the 1960's.   they've been used in all kinds of industrial and commercial applications as instrument signal lights.   using LED's as lighting instead of signaling has been around for a decade already in industrial and commercial.   it's only recently in past few years that it's reached consumer.  

as for testing, it's not needed to leave them on for 20 years.   you run thru an accelerated test for 30 days, then project the component wear results.   if the projected time of failure is beyond 20 something years,   that's good enough to say it'll be guaranteed for 20 years.