RAB Lighting announced that it now rates its LED-based lighting fixtures for 100,000 hrs of life, equating to 27 years based on a 10-hr usage day. The extended rating for the solid-state lighting (SSL) products is based in part on the TM-21 standard for projecting LED component lifetime that was released by the Illuminating Engineering Society (IES) last year.

Longer lifetime is a hot topic. Cree recently extended the warranty to ten years on most of its LED-based product line for commercial applications. For now, RAB has not addressed the warranty, but just the projected life. The extended life claim applies both to new and previously-released LED fixtures.

"TM-21 puts a stake in the ground and levels the playing field for LED fixture manufacturers," says Ross Barna, CEO of RAB Lighting. "RAB takes enormous pride in designing LED fixtures that perform as great as they look, so it was very gratifying to learn that our adherence to the strictest design standards and our LM-80 tests exceeding 10,000 hours have finally paid off."

In reality however, TM-21 is strictly-speaking an LED component standard. It's not meant to apply to a luminaire design where other sources of failure, such as the notorious electrolytic capacitor in the driver electronics, can cause system failure far before the LEDs reach end of life.

Thermal design

RAB did acknowledge the importance of system design, noting that its engineers develop robust thermal systems to keep the LEDs at proper temperature. The company said, "RAB engineers utilize state-of-the-art computational fluid dynamic software to study heat movement and airflow around LED fixtures." Still there are plenty of other failure modes.

We will also note that TM-21 calculations come in two flavors reported and calculated. The reported number to end of useful life is generally considered more valid. That number is limited to six times the LM-80 tested life used in TM-21 calculations.

LM-80 requires a minimum of 6000 hrs of testing and at the point the reported TM-21 life projection would be 36,000 hrs. After LED testing reaches 10,000 hrs, the reported life would be 60,000 hrs.

Apparently, RAB Lighting is basing its claims on a reported life projection so the LEDs that they are using would have been tested to the LM-80 standard for more than 16,000 hrs.

Conversely, calculated TM-21 results can be much higher and, while based on the same algorithm behind reported results, aren’t limited to six times the test duration . For instance, Cree contributed an article to LEDs Magazine earlier this year and used an example of real data with an LED projected to 290,000 hrs at L70 (more than 70% of initial lumen output).

Still, it bears repeating that LED life won't often be the determining factor in the lifetime of a well-designed SSL fixture. Don’t mistake lifetime projections for a warranty.