Long-Term Performance

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LED downlights in a long-term test rack.
The extended lifetime of LED products has been a distinguishing feature of the technology, even before the products were competitive in other performance areas. What’s unique about LEDs, however, is that they typically do not “burn out” like conventional incandescent and fluorescent lamps. This means that traditional methods do not work for rating the lifetime of LED products. Further, because of their extended lifetimes, considerable attention has been paid to understanding how the performance of LED products is maintained over time, particularly for lumen output and chromaticity (the color of the light). More information on the lifetime and reliability of LED products can be found in the DOE Technology Fact Sheet on the topic.

In collaboration with the IES and other standards organizations, DOE has played a key role in defining test procedures for long-term lumen and chromaticity of LED products, IES LM-80, IES TM-21, and IES LM-84. These methods have helped ensure consistent and reliable product information for specifiers and consumers.

DOE has conducted several investigations on long-term product performance, with the purpose of better understanding performance trends and making comparisons to conventional light sources. These include tests conducted in the Automated Long-term Test Apparatuses (ALTA) and Ambient Condition Test Racks at Pacific Northwest National Laboratory, and long-term evaluations of field installations. In addition to two ongoing projects focusing on LED downlights and LED modules, the following studies have been completed.

Photo of an integrating sphere below rows of installed LED light bulbs.
L Prize: Lumen Maintenance Testing of the Philips 60-Watt Replacement Lamp L Prize Entry: L Prize testing involved continuous operation and frequent measurement of 200 A-type lamps submitted for the competition. Testing began in 2010, and after 25,000 hours of operation, the average lumen output was greater than 100% of the initial, and the average Δu'v' was less than 0.002. A reduced sample continues to be operated and measured, and after 50,000 hour of operation, the average lumen output was 93% of initial, with an average Δu'v' still at 0.002. The ambient temperature was maintained at 45°C for the duration of the test. No catastrophic failures have occurred to date.

A testing chamber with rows of installed PAR38 lamps.
CALiPER Report 20.4: Lumen and Chromaticity Maintenance of LED PAR38 Lamps: With a setup and procedure similar to the L Prize testing, this experiment examined the performance of 38 different PAR38 lamps (32 LED, 2 CFL, 1 CMH, and 3 halogen) over 14,000 hours of operation at an ambient temperature of 45°C. On average, the lumen and chromaticity maintenance of the LED products was as good as or better than the competitors, but there was substantial variability.

 

A row of PAR38 lamps installed on a truss.
CALiPER Report 20.5: Chromaticity Shift Modes of LED PAR38 Lamps Operated in Steady-State Conditions: This report utilized the dataset from CALiPER Report 20.4, but examined specific shifts in u' and v' coordinates, rather than the aggregated Δu'v'. The chromaticity shifts were linked to specific physical features and underlying causes.

 

Rows of LED light bulbs installed in a testing chamber.
CALiPER Retail Lamps Study 3.2: Lumen and Chromaticity Maintenance of LED A Lamps Operated in Steady-State Conditions: Like L Prize and CALiPER Report 20.4, this investigation relied on PNNL’s Automated Long-term Test Apparatus (ALTA). Ten samples each of 17 different retail-available A lamps were monitored over 7,500 hours. Again, the results showed variability in the results. Seven of the 15 LED products tested showed sufficiently low output at 7,500 hours that they would not be expected to be above 70% output at their rated lifetimes.

Four photos of interior spaces with LED lighting.
GATEWAY Long-Term Evaluation of SSL Field Performance in Select Interior Projects: This report utilized data from previous indoor field installations and tracked the long-term performance of different technology platforms in a variety of applications: new luminaires at the Hilton Downtown Columbus (OH) Hotel, replacement lamps at St. Anthony Hospital (Gig Harbor, WA), retrofit kits at the Icahn Laboratory (Princeton University), and retrofit kits at the Clarice Smith Performing Arts Center (University of Maryland). The colorimetric and photometric performance is discussed along with the operations and maintenance of the LED systems.

Metrics and Test Methods