When a datasheet says 'L70 = 50,000 hours,' what's actually being promised? L70 = lumen-output at 70% of initial. B10 = the percentile of fixtures that hit that. Together: 90% of fixtures keep 70%+ output at 50,000 hours. The test chain is LM-79 (day-1) → LM-80 (LED-package aging, 6,000+ hours) → TM-21 (mathematical projection). Now you can read any LED claim.
Four ideas to carry into the next specification conversation you have.
L70 = 50,000 hours means lumens drop to 70% of day-1 at that point. L80 = 80%, L90 = 90% (much shorter time).
B10 = 10% fail by that hour. B50 = 50% fail. Premium specs: L70/B10 or L70/B20. Cheap: L70/B50 (half the fixtures already failed).
Real LED-package depreciation at 3 case temperatures (55, 85, 105°C). TM-21 maths extrapolates max 6× the test time.
LM-80 at 85°C ≠ Saudi parking garage at 65°C ambient. Always verify the test temperature matches the install environment.
What each notation actually means in field-installed years.
| Claim | Meaning | Real life (~10h/day) |
|---|---|---|
| L70 / 50,000 hr | 70% lumens at 50k hr, 50% pass | ~14 years |
| L70/B10 / 50,000 | 70%, 90% pass | ~14 years premium |
| L80 / 36,000 hr | 80% lumens at 36k hr | ~10 years |
| L90 / 25,000 hr | 90% lumens at 25k hr | ~7 years |
| Useful Life (LED) | L70 + minimal failures | Manufacturer spec |
Five questions to ask any vendor claiming 50,000+ hours.
Big difference. B10 means 90% of fixtures still work. B50 means half are dead. Premium projects demand B10 or B20.
LM-80 tested at 55/85/105°C. If your install runs hot (high-bay, recessed in insulated ceiling), the real L70 is much shorter. NLC reports L70 at three temperatures.
LM-80 measures LED only. LM-84 measures whole luminaire including driver. Driver fails before LED in most cases, ask for both.
TM-21 limits extrapolation to 6× test time. 6,000-hour LM-80 → 36,000-hour max projection. 10,000-hour LM-80 → 60,000-hour max. 'L70 = 100,000 hours' from 6k-hour LM-80 is mathematically invalid.
LED chip might last 100k hours. Driver electrolytic cap at 85°C lasts 30k. Driver fails first. Premium: capless drivers or robust film-cap designs.
NLC datasheets show L70/B10 at 25/45/65°C ambient, driver lifetime, and LM-84 whole-fixture data. Real numbers you can plan around.
Practical lighting know-how from NLC Academy. No spam, unsubscribe anytime.
By subscribing you agree to receive NLC emails.