The lifetime of a LED lamp is defined in hours. As with all types of lamp, the light output very slowly fades over time. LED lamps do not generally burnout they will still perform after their rated hours e.g 25,000 hours.
The lifetime is the figure stated when the light output is predicted to drop by a significant amount of the original light output where you may consider a replacement, this is partly due the the slow aging of the parts of the lamps such as refractors and other components. External factors such as heat, humidity, switching cycles and power supply will affect the lifetime of an LED lamp.
The table below gives an indication and comparison with filament and CFL lamps on how many years a LED lamp rated at 25,000 hours will operate.
As you can see a LED lamp will last over 22 years (at 3 hours per day) against a filament lamp of less than a year and a CFL of just over 9 years.
The longer life of LED means less time spent on lamp changes (important for hard-to-get-at areas) . Also it's great for the enviroment with less lamps, packaging and transport energy being used.
|lifetime in Years
All lamps including LED have a number of switching cycles. This is the minimum number of times the bulb can be switched ON and OFF before failure in normal use, lamps may go on to last longer. For a typical value of 12,500 the lamp can be switched ON and OFF once a day for a minimum of 34 years! (Environmental factors such as temperature can affect the value). In general, LED lamps for home or office use are not designed to be switched ON and OFF rapidly.