Due to chemical and physical changes, LED modules lose some of their luminance over their service life. This degradation over the service life is denoted by the LX value, which speciﬁes the luminous ﬂux still reached following the rated service life of the LED modules. For example, a value of L70 at 50,000 hours means that 70% of the initial luminous ﬂux will still be attained after 50,000 hours.
In addition to the failure rate CZ, the percentage value BY is equally decisive for the rated service life LX. The BY value speciﬁes the percentage share of LED modules that are permitted to fall short of the LX value. A common value is B50, which means that 50% of all modules can fall short of the L70 value after, for instance, 50,000 hours.
This means that the service life of LED modules is speciﬁed in consideration of both a gradual (e.g. L70/B50) as well as sudden (e.g. L0/C10) decrease in luminous ﬂux, which ensures both the effects of ageing and the total failure of an LED module are taken into account.
For drivers with CLO function, the decrease in luminous flux can be compensated by programming the driver accordingly.