LED lights characteristically fade over a very long period of time.
The “lifetime” of an LED is generally accepted to be when the luminous output drops to 70% of its original intensity.
A power LED industry group, Alliance for Solid-State Illumination Systems and Technologies (ASSIST) conducted tests in a commercial lighting environment that showed people generally accepted a diminished light output of 70% of its original brightness. This value is known as L70.
Some small lamps may claim an L70 of 15,000 hours. Larger recessed downlight systems may claim an L70 of 50,000 hours or more.