Maintenance Factor (MF)

Maintenance factor is the multiplier a lighting design applies to account for the light a system will lose over its service life — LED lumen depreciation, dirt building up on optics, and room surfaces dulling. A design with MF 0.8 must deliver 25% more initial light so the installation still meets its target lux at the end of the maintenance cycle, not just on day one. It is the product of factors for lamp lumen maintenance (from LM-80/TM-21 data), luminaire dirt, and surface depreciation, and it varies with environment: a clean office might justify 0.8, a dusty steel mill closer to 0.6. If a supplier’s layout quotes average lux without stating the maintenance factor, ask — omitting it is the easiest way to make a thin design look compliant.