Maintenance factor: why designs start above the target

Sports standards specify maintained illuminance — the minimum average level the installation must still deliver just before maintenance. Light output falls from day one, so the initial design must be higher.

What reduces light over time

• Lumen depreciation of the LEDs, which depends on operating temperature, drive current and hours.
• Dirt on the lens, which depends on environment (dust, coastal salt, pollen, birds) and how often fixtures are cleaned.
• Luminaire failures between maintenance visits.

The maintenance factor

The design calculates initial levels, then multiplies by a maintenance factor (MF) — often 0.7–0.9 depending on assumptions — to check the maintained result. A design with an MF of 0.8 starts 25 % above the target.

Making it work for you

• State the assumptions. An MF is only meaningful with the assumed operating hours, cleaning interval and environment written next to it.
• Use dimming to hold levels constant. With controls, an installation can run at reduced output when new and step up over the years (constant light output). The field gets the same light; the early years use less energy.
• Clean on schedule. In dusty climates, lens cleaning can recover more light than any other maintenance action.