What causes LED bulbs to age and stop working?

[iScience]

i'm shopping online for an LED bulb and one site gives the estimated lifetime of the LED.

So, i was wondering what exactly is happening to make the device "old" and no longer work?

 

[Baluncore]

http://en.wikipedia.org/wiki/Light-emitting_diode
http://en.wikipedia.org/wiki/List_of_LED_failure_modes