A long time ago Nichia invented the white 5 mm LED. In testing under controlled laboratory conditions they estimated 100,000 hour lifetime. So in the early '00s everybody claimed 100,000 hours (even when they use crap Chinese clone LEDs). Most last a few weeks to as low as 20 hours under actual continuous running.
When Lumileds came out with the Luxeon a more rugged design with a means to heatsink it, the claim was 50.000 hours and with proper heatsinking can actually meet the claim. More recent LEDs use the Luxeon as a design base and most can do 50,000 hours AT 25°C (a laboratory standard temperature).
But LED light bulbs run the LEDs up to 85°C so many LEDs deteriorate faster than the base 50,000 hour claim. In addition electrolytic capacitors self destruct at 65°C meaning a lot of badly designed or built bulbs do not last as long.
The original claim is based on copying and pasting a number from Lumiled's or Cree's website. (Just like those cheap DX flashlights.)
UL got smart and won't do the safety approval test unless the bulb has gone through preliminary testing of basic features by an approved North American lab - brightness, colour temperature, estimated runtime to 70% brightness etc.
All of a sudden, the maintenance of brightness at 85°C and the shorter life of the capacitor(s) showed up and a more realistic number emerged.
Still in actual testing by Consumer Reports a lot of LED bulbs do not meet the reduced claim of 20,000 to 30,000 hours.
25,000 hours means 2.5 years continuous running, 5 years at 12 hours a day, 10 years at 6 hours a day, 20 years at 3 hours a day.
My personal experience with a cheap G45 no name bulb rated for 20,000 hours lasted 15,000 hours. 1 year 10 months 24/7. I said cheap because I found the circuit board with the LED on it is not thermally connected to the thin strip of metal on the outside.
