What is a maintenance factor?

As well as lumen depreciation, dust/dirt accumulation on light fittings and room surfaces will affect light levels in the intervals between cleaning. To account for these (and other variables) a "maintenance factor" is used in lighting designs. This is a number ranging from 0-1 (typically 0.8 is used for LED products by default)and it is multiplied by the results of the design calculations with the aim of simulating lux levels at a particular point in product lifetime/cleaning cycles. This is almost always taken to be the mid-point unless stated otherwise. It is important to consider that if you are comparing designs with the same maintenance factor and one product has a much longer lifetime than the other, the light levels from the longer lifespan product will remain higher than the simulated maintenance factor for longer.