One of the greatest benefits of LED technology is its lifespan.
It is widely understood that LED light sources outlast previous light sources, typically by many years of use. However, the 'lifespan' of an LED is commonly misunderstood.
When a traditional light source, e.g. a halogen bulb, reaches the end of its lifespan it will fail abruptly and stop working entirely. By comparison, LED light sources gradually fade over time until they become too dim to produce usable light.
So, if LED's do not reach a clear or abrupt end to their life, how do we assess how long an LED will 'last'?
LED lifespans are defined using L and B ratings, in combination with hours of operation.
These ratings are determined through LM-80 testing.
What do L and B numbers mean?
L defines the remaining amount of light produced by an LED compared to its initial output at a given point in time.
Example:
A rating of L70 B20 50,000hrs indicates that the LED will produce 70% or more of its initial light output at 50,000 hours of operation.
A rating of L80 B20 50,000hrs indicates that the LED will produce 80% or more of its initial light output at 50,000 hours of operation.
In this case, the higher the number, the better the quality.
B defines the acceptable failure rate of the L rating.
Example:
A rating of L80 B50 50,000hrs indicates that up to 50% of the LED's will not achieve 80% of their initial output at 50,000hrs hours of operation.
A rating of L80 B20 50,000hrs indicates that up to 20% of the LED's will not achieve 80% of their initial output at 50,000hrs hours of operation.
In this case, the lower the number, the better the quality.
A lifetime rating of L70 was the initial benchmark for quality integrated LED light sources. A technology has improved, ratings of L80 and L90 are now achievable. Similarly, a failure rating of B50 was the initial benchmark, which has now raised to B20 or B10.
There are two other, less commonly used, ratings that relate to the performance of LED’s
C-Value defines the expected percentage of catastrophic fails when an LED module emits no light. This is extremely uncommon in LM-80 certified LED chips.
F-Value depicts the combined failure fraction. This is is a sum of the B and C values (F=B+C).
Hours of operation - Integrated LED vs Retrofit Lamps
All LED light sources require more sophisticated circuitry than traditional light sources. This circuitry requires effective heat management.
The physical size of a retrofit LED lamp limits its capacity for heat management. As a result, most retrofit lamps have a typical hour rating of approx. 10,000 to 15,000 hours. If used within an enclosed light fitting where heat cannot dissipate easily, this would reduce even further.
Integrated LED luminaires effectively manage heat through integrating heatsinks into the luminaire design. This increases their capacity for heat management significantly. As a result, integrated LED luminaires typically have a much higher hour rating of 50,000hrs to 100,000hrs.
