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Lighting FundamentalsSpecification
Maintenance Factor & Light Loss
Why your new installation will be 20–30% dimmer in 5 years — and how to plan for it.
5 min LEDWORLD Technical Team 363 views
The Formula
Maintenance Factor (MF) = LLMF × LSF × LMF × RMF LLMF = Lamp lumen maintenance factor (LED aging) LSF = Lamp survival factor LMF = Luminaire maintenance factor (dirt/dust) RMF = Room maintenance factor (surface degradation) Typical MF for a well-maintained clean indoor space: 0.8 For outdoor or dusty environments: 0.6–0.7
Typical Maintenance Factors
| environment | mf | notes |
|---|---|---|
| Clean office (LED) | 0.80 | Regular cleaning, 50,000hr L70 LEDs |
| Hotel guest room | 0.80 | Good housekeeping |
| Retail (clean) | 0.75–0.80 | Depends on store type |
| Industrial/warehouse | 0.65–0.70 | Dust accumulation |
| Outdoor (covered) | 0.70 | Weather exposure |
| Outdoor (exposed, GCC) | 0.60–0.65 | Sand, heat, UV |
What L70 and L80 Mean
LED life is rated as Lxx at a given number of hours. L70 @ 50,000hrs means the LED retains 70% of its initial output after 50,000 hours. L80 means 80% retained. Higher Lxx numbers mean less degradation — look for L80 or better.
Before You Specify
Always apply MF to your lux calculations — never design to initial output
Check the LED manufacturer's L70/L80 data at the specified drive current
Factor in your cleaning schedule — dusty environments need lower MF
For GCC outdoor: use MF 0.60–0.65 due to sand, heat, and UV
Over-specify by 20–30% to maintain lux targets at end of design life
Common Mistakes
Designing to initial lumen output without MF — space is under-lit within 2 years
Using MF 0.8 for dusty industrial environments — too optimistic
Ignoring room surface degradation — dark walls absorb more light over time
Not checking LED rated life at the actual drive current being used
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