LED lifetime test: the IESNA LM-80 standard

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LED Lifetime - how to calculate it?

The IESNA LM-80 standard is the internationally recognized way for Lumen Maintenance Testing of LED light sources, arrays and modules. In other words, it clarifies the way LED brightness depreciation over time is measured. Without this standard, a manufacturer could manipulate the testing in order to obtain values that makes his LEDs stand out from the competition even if their actual quality is sub-standard. A market full with low cost products with 50.000 claimed LED lifetime shows how dire the need is for standards.

The result of IESNA LM-80 can look like this:

 What does it show:

The Lumen Maintenance at 6000 hours, as percentage, where 100% is initial, measured value.

What does not show:

 Determination or estimation of expected life or lumen output beyond test data.

Details required by LM-80:

• drive current for the LEDs tested. The manufacturer can decide the drive current for each LED type which usually includes the typical value, the maximum value and an intermediary value from it datasheet.

• for each drive current the LEDs must be tested at three ambient temperatures (Ta). The manufacturer has the freedom to choose one, the others are 55°C and 85°C.   

How LM-80 prevents misleading test results:

• Testing must be made in a 3-rd party Internationally Recognized Testing Laboratory. The manufacturer can use its own lab only if it accredited for the specific testing by a national or international Accreditation body.
• Intermediary results must be measured and recorded, at least at each 1000 hours.
• Testing and measuring equipment is properly calibreated
• Every aspect of testing is recorded

Results of the test must include: 

• Description of Sources tested
• Sample size
• Ambient conditions (Airflow, temperature, RH etc)
• Case Test point temperature
• Electrical conditions
• Lumen maintenance data
• Observation of failures
• LED monitoring interval
• Chromaticity shift over time

Without testing according to the LM-80 standard any measured lifetime claim is unfounded and must be received with a high degree of scepticism.

All major LED producers now follow the LM-80 testing standard, among them Nichia, Cree, Philips, Osram, Bridgelux and many others.