Every LED lifetime figure on a datasheet — "L70 50,000 hours" — comes from an LM-80 test program: a multi-month accelerated aging study far more involved than a single photometric measurement.
Why LEDs Need a Different Lifetime Test
Traditional light sources fail catastrophically; LEDs degrade gradually, with light output slowly declining over thousands of hours. This is why IES developed LM-80 — measuring how output and colour drift over time rather than waiting for a failure event. L70 (time to 70% of initial output) has become the de facto "useful life" standard.
The LM-80 Test Protocol
Three temperature conditions, run concurrently — 55°C, 85°C, and a third manufacturer-chosen condition, needed to characterise how degradation scales with thermal stress.
Minimum 6,000 hours, 10,000 recommended — the test duration directly limits how far the resulting lifetime projection can credibly extend.
Periodic measurement, typically every 1,000 hours — building out the degradation curve rather than relying on just two data points.
Constant current operation — isolating photometric degradation as attributable to the LED chip itself rather than any drift in a driving supply.
What Equipment This Actually Requires
- Temperature-controlled chambers for each of the three conditions, holding stable setpoints (typically ±0.5°C)
- Integrating sphere photometry, sized for the samples under test, allowing flux measurement without removing samples from their aging condition
- Constant-current LED driving circuitry, precisely regulated
- Multi-sample capacity — testing a meaningful sample size across multiple chambers
- Data logging and analysis software implementing the TM-21 extrapolation model
This is meaningfully different equipment from LM-79 testing capability. The LISUN LEDLM-80PL is a representative LM-80 LED aging test system.
From Test Data to Lifetime Claim: TM-21
TM-21 defines how to turn LM-80 data into the lifetime figure on a datasheet, using an exponential decay model and the Arrhenius equation. The critical constraint: a projection can extend no further than six times the actual LM-80 test duration. Run the 6,000-hour minimum, and the maximum defensible projection is 36,000 hours — meaning a 50,000-hour claim needs at least 8,334 hours of underlying data.
This is worth checking when evaluating a supplier's lifetime claims: a 50,000-hour rating built on a 6,000-hour dataset has exceeded TM-21's extrapolation limit.
Reading the Output
| Output | Meaning |
|---|---|
| L70 (projected) | Hours until flux degrades to 70% of initial |
| Δu'v' (chromaticity shift) | How far colour has drifted — LEDs can fail on colour shift before significant lumen depreciation |
| Maximum valid extrapolation | 6× the actual test duration, per TM-21 |
Why This Matters Beyond Compliance Paperwork
Comparing degradation curves across LED packages, drive currents, or thermal designs reveals which configurations age gracefully, often well before 6,000 hours have elapsed. An in-house LM-80 capability shortens the feedback loop between a design change and knowing whether it improved long-term performance.