LEDs are considered the most efficient light source. Another important advantage that LEDs offer is their longevity. The light intensity of the LEDs decreases over time during the usage period. Therefore, LxBy parameters such as L90B10, L80B10, L70B50 are used to indicate the lifetime of LED luminaires.
LxBy parameter specifies when the luminaire’s lifetime will expire and how large the margin of error is in its operation. The standard LxBy terminology includes two indicators. For this reason, its reading is divided into two parts, Lx and By. The L value indicates the minimum of the luminous flux to be maintained during a certain period of use. The B value indicates the error rate. This refers to the time it takes for y% of the LEDs to reach x% of the initial flux at the specified maximum ambient temperature.
For example; In a luminaire specified as L80B10, 50,000 hours, after 50,000 hours (approximately 16 years), 10 percent of the LEDs will have a luminous flux of less than 80 percent of the initial luminous flux. In an other saying; The luminous flux of 90 percent of the LEDs is maintained so that it does not drop to less than 80 percent of the initial flux.
If the L70B50, 50,000 hours, that means that after 50,000 hours, only 50 percent of the LEDs have more than 70 percent of the initial lumen. So the light degradation of L70B50 is faster than L80B10. If you have to choose between the two, choosing the L80B10 is the right one.
In LED lighting applications, it is desirable to have a high L value and a low B value. Accordingly, it is possible to say that L100B0 is the best. However, it is impossible to achieve. It is a natural process that the light output of LEDs decreases over time.
A 30 percent drop in initial luminous flux is considered the threshold for human perception. Therefore, the generally accepted measure of life for LED light sources is the time it reaches 70 percent of the initial flux. It is recommended to replace the LED lighting fixtures used in indoor lighting when they reach 80 percent of the initial luminous flux. For street lighting, this ratio is recommended as 90 percent.
The LB value is the best way to show the life of the LEDs. Unfortunately, a limited number of manufacturers provide information on LxBy parameters.
