Unlike other light sources, LEDs usually don't "burn out". Instead, they get progressively dimmer over time (a process called "lumen depreciation"). As a result of this, it is important to understand an LED lighting manufacturer's life claims relative to light output.
LED useful life is typically based on the number of operating hours until the LED is emitting 70 percent of its initial light output (usually denoted by an "L70" suffix on the expected life figure quoted). Good-quality white LEDs in well-designed fixtures are expected to have a useful life of 50,000 to 60,000 hours (L70) with some highly evolved designs exceeding 100,000 hours (L70).
A primary cause of lumen depreciation in an LED light is the level of heat generated at the LED junction. The efficiency of the heatsink design and the thermal efficiency of the materials transmitting that heat away so as to remove that damaging element are therefore pivotal in securing extended design life.
LEDs do not emit heat as infrared radiation like other light sources, so the heat must be removed from the device by conduction or convection and thermal management is arguably the most important aspect of successful LED system design. In inferior designs this is generally the limiting factor.
A typical incandescent lamp lasts about 600 to 800 hours; a comparable CFL lasts 6,000 to 10,000 hours, and the best linear fluorescent lamps can last more than 30,000 hours but again this anticipated life is dependent on real-time running temperatures. Enclosed MR16 and GU10 downlight bulbs can typically last between 200 to 400 hours.