If you’ve ever delivered a lighting installation that looked dimmer than the calculations predicted, the Maintenance Factor (MF) is likely where the gap occurred. It’s one of the most important — and most frequently misapplied — parameters in professional lighting design.
What Is Maintenance Factor?
Maintenance Factor is a multiplier (always less than 1.0) applied to initial luminaire output to predict maintained illuminance over the life of the installation. It is the product of four components:
- Lamp Lumen Maintenance Factor (LLMF): LED output reduction over time, expressed as L70 (point at which output reaches 70% of initial)
- Luminaire Dirt Depreciation (LDD): Reduction from dust and contamination on optics, diffusers, and the luminaire body
- Room Surface Dirt Depreciation (RSDD): Reduced reflectance from dirty walls, ceilings, and floors
- Lamp Survival Factor (LSF): For multi-source installations, the proportion of sources still operating at the calculation point
MF = LLMF × LDD × RSDD × LSF
Typical MF Values by Environment
| Environment | Typical MF | Maintenance Assumption |
|---|---|---|
| Clean office | 0.80–0.85 | Annual cleaning |
| Retail | 0.70–0.80 | Bi-annual cleaning |
| Industrial / warehouse | 0.55–0.65 | Dusty, 3-year cycle |
| Clean room / laboratory | 0.85–0.90 | Frequent cleaning |
| Outdoor (IP65) | 0.65–0.75 | 3-year maintenance cycle |
The Most Common Mistake
Using a generic MF of 0.8 for every project regardless of context. A dusty factory with a 5-year maintenance cycle and an assumed MF of 0.8 will be significantly under-lit within 2 years. Conversely, applying a conservative MF of 0.55 in a clean, well-maintained office results in expensive over-specification and unnecessary energy use.
MF in DIALux EVO
DIALux EVO allows MF to be set per room or per luminaire group. Use the LLMF data from the manufacturer’s LM-80 test report for accurate lamp depreciation figures. Calculate LDD based on the luminaire’s IP rating and the cleaning schedule documented in the project maintenance plan.
Lumengraphix Practice
At Lumengraphix, we document MF assumptions in every calculation report — including the maintenance schedule on which the MF is based. This creates a clear accountability framework: if the installation is not maintained as specified, the client cannot expect designed illuminance levels to be sustained. This is professional practice that protects both the designer and the client. Get in touch to discuss your project.