Lighting
Lighting maintenance factor
- where
- maintained illuminance (lx)
- initial illuminance (lx)
- maintenance factor
Explain this equation
Gives the illuminance expected at the end of a maintenance period from the initial illuminance. Use it to see what a new installation will fall to.
E_initial is the illuminance when the installation is new and clean, in lux. MF is the maintenance factor, a decimal below 1 that combines falling lamp output, lamp failures, and dirt on luminaires and room surfaces. E_m is the maintained illuminance, the level the design must still meet before cleaning or replacement.
Ageing and dirt each cut output by a proportion, so a single multiplier scales the initial value down.
500 lx when new with MF 0.8 gives 400 lx maintained. Clean spaces with good LED products may reach 0.8 to 0.9; dirty or poorly maintained spaces can be much lower.
Watch out: to find the initial level needed for a maintained target, divide by MF, don't multiply. MF depends on the product, the environment and the cleaning plan; it is not a fixed number.
Initial light output declines over time and dirt affects the luminaire and room. Maintenance factor connects the initial design calculation with the maintained value expected under a stated maintenance plan.
To find the initial illuminance needed, divide the maintained target by MF. The result is greater than the target when MF is below one.
Enter your values to see the result.
Common mistake
Do not multiply the maintained target by MF when finding the greater initial value required.
Limits
Choose factors from actual product data, environment, replacement and cleaning plan. MF is not a universal constant. This does not establish a statutory target.
Sources
The tools calculate the displayed equation. They do not automatically choose cable sizes, approve installations, supply current regulatory tables, certify equipment or replace inspection and testing.