One of the key advantages of LED technology compared to other lighting technologies is its reliability and long operating life. The light output of an LED tends to gradually degrade over an extended period of time, compared to a halogen or incandescent light source which fails abruptly.
The abrupt failure of traditional incandescent sources is shown in brown, compared to the gradual decay of LED sources
Incandescents are deemed as ‘failed’ when the fillament breaks and the bulb no longer emits lights, LED’s however will gradually decrease in light output over an extended period of time. This raises the question, what constitutes a failure point or lifetime of an LED. To solve this, the LED industry developed the IES LM-80 and TM21 standards which specifies how LED manufacturers can test LED components to determing their performance over time. As a result lifetime predictions where measured in terms of L70, which is the point at which the light source is at 70% of its initial lumens (or a 30% loss in output).
As LED technology developed, lifespans increased and the 70% figure of L70 was commonly being reached at durations exceeding 60,000 hours. This lead the industry to adopt additional ratings such as L80 (80% of initial lumens) and L90 (90% of initial lumens). In other words a fitting rated at 50,000 hours L90 would retain 90% of its light output at 50,000 hours, whereas a fitting rated 50,000 hours L70 would only retain 70% of its output.
The failure fraction for By expresses only the gradual light output degradation as a percentage y of a number of LED modules of the same type that at their rated life designates the percentage (fraction) of failures. The value B50 indicates that the declared L-value will be achieved by minimum 50 % of the LED modules and that the remaining 50% may have a lower lumen value. The value B10 means that minimum 90 % of the LED modules will meet the declared L-value and only 10% will have a lower flux level.
Grah Luminaries have rating L90 B10 at 100.000 hours.