Kristin Lewotsky writes:
LEDs have a well-deserved reputation for high-efficiency operation, not to mention high reliability. Properly specified and implemented, LEDs should and do satisfy virtually every lighting application. Still, there are times when actual device lifetimes fall short of the specified ideal. LEDs are wide-bandgap semiconductor devices. As a result, they have far more complex and varied failure modes than the incumbent technologies. Unlike an incandescent lamp, where failure is fairly simple (the bulb produces light until the filament breaks), with an LED, the failure modes range from mechanical and electrical to material.
Via and Source: Electronics-Lab