Why do LED lamps become dimmer over time?
– Physical mechanism of lumen depreciation & industry standard explained
1. Phenomenon: Getting dimmer is not your imagination
Many customers report that a new LED lamp starts very bright, but after one or two years it becomes noticeably dimmer. This is not visual fatigue – it is lumen depreciation: the inevitable decline in luminous flux of an LED chip as cumulative lighting time increases.
2. Root cause: Heat is the #1 killer
About 70%–80% of the electrical energy consumed by an LED chip is converted into heat. For every 10°C rise in junction temperature (Tj), the depreciation rate approximately doubles. High temperature causes:
- Decreased quantum efficiency of the phosphor
- Carbonization and yellowing of encapsulation materials (silicone/epoxy)
- Metal migration on electrodes, forming dark areas
3. Key data: Lumen depreciation comparison of different LED grades
Based on LM‑80 test data and TM‑21 projections:
| LED grade | Test condition (junction temp) | Lumen maintenance at 6,000h | Projected L70 life (to 70% of initial) |
|---|---|---|---|
| Low‑grade chip | 85°C | ≤ 85% | < 15,000 hours |
| Commercial grade | 85°C | 90% – 92% | ~25,000 hours |
| Premium industrial grade | 105°C | ≥ 94% | > 50,000 hours |
| Top‑tier brand (e.g., Lumileds/OSRAM) | 105°C | ≥ 96% | > 60,000 hours |
Conclusion: After the same 6,000 hours of operation, a low‑grade LED is already "semi‑retired," while a premium LED still shines like new.
4. How to choose long‑life LED luminaires?
- Look for an LM‑80 report – Reputable brands provide third‑party LM‑80 test data verifying lumen maintenance.
- Check the thermal design – Touch the driver housing or heat sink; if the temperature stays below 60°C after 30 minutes of operation, the design is good.
- Consider the warranty period – Brands that confidently offer 5+ years of warranty usually have better control over lumen depreciation.
5. One‑sentence summary
Lumen depreciation is the "chronic aging" of LEDs – thermal management determines lifetime, and data is more reliable than marketing slogans.
Should you have any requirements for bulk purchasing or customized lighting solutions, please do not hesitate to contact us for a detailed quotation.
