LED lifetime according to the LB standard
Published on: 24 januari, 2022
The lifespan of your LED lighting is a lot longer than that of halogen or fluorescent lighting. The number of operation hours is still being increased in new generations of LED luminaires and light sources. What is the meaning of that number and what happens at the end of that lifetime?
Decreasing light output
A LED module or LED chip is made out of many small diodes, usually under a yellow layer of phosphor that defines the quality of the light. By using smaller and better diodes, the light output and efficiency are getting up every year. But also the indicated lifespan is increased to an average of around 100,000 hours. At 60 hours per week, that is about 30 years. At the end of that period, you won’t see all the individual diodes fail at the same time. After a good amount of years, the light will just slowly start fading.
What exactly does 50,000 or 100,000 hours mean? We specify the decline in light output for a certain part of the light sources by means of the LB standard. The L-value expresses the drop in light output and the B-value indicates the amount of light sources that must comply. L is a percentage of the original light output after the specified number of service hours and B is the percentage that could be performing worse – in the worst case scenario. ‘Worst case’ means – for example – many switching cycles (for instance a PIR sensor in a corridor area) and relatively unfavourable temperature and humidity. If the LB is not given, L70B50 is assumed, meaning a light output of still 70% for at least half of the light sources. A higher L-value means less drop. A lower B-value means a more reliable lifespan indication.
In a project we supply 240 downlights 13W 2000lm with a lifetime of 50,000 hours L90B50 on the spec sheet. The project is open 5 days a week and the lights are on 12 hours a day. After about 16 years the light output per downlight is still 90% - 1800lm. This applies to at least 120 luminaires, because we know that a maximum of 50% can perform worse in the worst case scenario.
In some cases, more than one LB-value with different lifetimes are given. For example 149,000 hours L80B10 and 70,000 hours L90B10. If the 90% light output is already a critical limit, you have to act after 70,000 hours. If you can still work with >80% light output, you have more than twice the amount of hours before the fixtures have to be replaced.