LED manufacturers quote lifespan figures like "L80/B10 50,000 hours" but rarely explain what those numbers mean in practice. Understanding these ratings helps you make informed decisions about product quality, maintenance planning, and total cost of ownership.
The L Rating: Lumen Maintenance
The L number describes how much light output remains at the rated lifespan. L80 means 80% of the original lumen output. L70 means 70%. The higher the L number, the better the lumen maintenance.
All LEDs gradually lose brightness over their operating life. This is called lumen depreciation. A fitting rated L80 at 50,000 hours will still produce 80% of its initial light output after 50,000 hours of operation. At that point, the fitting has not failed. It is still working. It is simply 20% dimmer than when it was new.
Common L ratings you will encounter:
| Rating | Light remaining | Typical use |
|---|---|---|
| L90 | 90% | Premium architectural fittings |
| L80 | 80% | Standard commercial fittings |
| L70 | 70% | Budget or industrial fittings |
For most commercial projects, L80 is the accepted standard. L90 is preferred for high-specification environments where consistent light levels matter, such as retail displays, art galleries, and healthcare settings.
The B Rating: Failure Fraction
The B number describes what percentage of a batch might fall below the stated L rating at the rated lifespan. B10 means no more than 10% of fittings will have dropped below the L rating. B50 means up to 50% might have dropped below.
This is a statistical measure. B10 is more conservative and more reliable. B50 is the median, meaning half the fittings in a large installation might be below the stated lumen maintenance level.
When a manufacturer quotes "L80/B10 50,000 hours", they are saying: after 50,000 hours of operation, at least 90% of the fittings will still produce 80% or more of their original light output.
If they quote "L70/B50 60,000 hours", they are saying: after 60,000 hours, half the fittings might have dropped below 70% of original output. This sounds like a longer life, but the standard is less demanding.
What the Hours Mean in Practice
50,000 hours sounds like a lot. How does it translate to years?
| Usage pattern | Hours/year | 50,000 hrs = |
|---|---|---|
| Office (12 hrs/day, 5 days/week) | 3,120 | 16 years |
| Retail (14 hrs/day, 6 days/week) | 4,368 | 11.5 years |
| 24/7 operation (hospital, car park) | 8,760 | 5.7 years |
| Corridor with occupancy sensor | ~2,000 | 25 years |
For a typical office, 50,000 hours is roughly 16 years of real-world use. In most cases, the fitting will outlast the interior fit-out cycle (typically 7-10 years). The building will be refurbished before the LEDs need replacing.
Why This Matters for Specification
When comparing products, look at the full lifespan statement, not just the hours. A fitting quoted as "L80/B10 50,000 hours" is a better specification than one quoted as "50,000 hours" with no L or B qualification. The second product might only achieve L70/B50, meaning significantly worse real-world performance.
For lighting design calculations, use the Maintenance Factor (MF) to account for lumen depreciation over the design life. If you specify L80 fittings with a 5-year maintenance cycle, your maintenance factor for LED depreciation (LLMF) would be approximately 0.9. Your lighting designer includes this in the calculation to ensure lux levels stay above the minimum throughout the maintenance period.
Beyond the LED: Total Luminaire Life
The LED chip lifespan is only part of the story. The LED driver (power supply) is typically the component that fails first. Quality drivers from established manufacturers (Tridonic, Osram, Mean Well, Philips Xitanium) are rated for 50,000-100,000 hours. Budget drivers can fail in under 20,000 hours.
Other factors that reduce real-world lifespan: poor thermal management (overheating degrades LEDs faster), surge events on the electrical supply, and incorrect dimming compatibility causing driver stress. A well-designed luminaire manages all of these through proper heat sinking, surge protection, and driver-dimmer compatibility testing.
What to Specify
For commercial projects, specify L80/B10 50,000 hours as the minimum. For premium applications, specify L90/B10 50,000 hours. Always check the driver specification separately and confirm the dimming compatibility with your chosen control system.
EMPRICS products display lifespan and lumen maintenance ratings on every product page. Browse our catalogue or request a specification for your project.