BASICS 12 of 19
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Lamp Mortality As lamps age their failure rate increases


TYPICAL LAMP MORTALITY CURVE

Lamps fail at an increasing rate. Typically, about 10% of lamps will have died by 70% of rated life, and, of course, 50% will die by "rated life."

Among humans a "life expectancy" of 76 years does not mean that all humans will die on their 76th birthday. Similarly, it is important to realize that a rated life of 20,000 hours does not mean that a group of lamps will work for 20,000 hours and then suddenly die—all at the same time..

Rated lamp life—also called average life—is defined by lamp manufacturers as that point in time when half of an initial set of lamps will have failed.

The lamp mortality curve on the left shows the percentage of lamps surviving as a function of time.