High-quality LEDs can maintain their light output for tens of thousands of hours. The built-in electronic driver,however, may show a sudden failure so the led bulb lifetime of the whole lighting system has to be considered.
The LED lamp lifetime is deﬁned as the period during which a given fraction of the total number of lamps (By) provide more than a pre-deﬁned percentage of the rated luminous ﬂux (lx), under standard test conditions,
e. g. L70B50 > 25,000 hours means that no more than 50 % of the lamps give less than 70 % of the rated luminous ﬂux after they have been used for 25,000 hours.
Rated led bulb lifetime should be balanced with price considerations, bearing in mind that for LED light sources with a very long rated lifetime, it may be proﬁtable to replace them before the end of their life cycle with new LED products with substantially higher efﬁciency – currently new, more energy efﬁcient LED products appear on the market every six months.
LED luminaire performance is inﬂuenced by the ambient temperature. The rated ambient temperature (ta) is the highest sustained temperature at which the luminaire may be operated under normal conditions.
Temperature tq (quality) indicates the highest rated ambient temperature permitted for a deﬁned level of performance (incl. rated lifetime and lighting characteristics). More than one tq value can be declared for
different performance characteristics