Accurate Maintenance Factors - Part Two (Luminaire Dirt Depreciation)

In 1962 the author outlined the need for accuracy in deriving and using "Maintenance Factor," recognizing that this is the designer's ultimate resource for predicting or expressing the performance of a lighting system. The economy of purchasing and operating such a system can depend on his use of an accurate factor because the amount of light actually delivered, in relation to that designed to be delivered, depends on such accuracy. Along with this design prediction must go the prediction of, and adherence to, a properly planned physical program of maintenance - or the recognition that no program is planned or will be performed.

"Maintenance Factor" is, in essence, the final result of measuring the various reductions in light output stemming from all the causes of light loss. These causes are relatively well known and understood in themselves. It is in recognizing and assessing them that deficiencies occur. Accuracy and completeness in such assessment is important for this represents the effective accuracy in predicting the performance of the lighting system. These causes of light loss are shown graphically and are discussed.