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The economics of lighting maintenance

Currently available data on the three deteriorations which reduce illuminances in a lighting installation—lamp lumen output, lamp survival and luminaire light output ratio—are examined: functions of the form u + (1 - u)e - pt are found to be satisfactory fits. Four alternative maintenance strategies are considered and expressions derived in each case for the annual cost of operating the installation. Where bulk maintenance is involved, there is a specific luminaire cleaning interval and a specific relamping interval which minimise the operating cost. These intervals can both be expressed in the form T = (r/Δ)1,2, where r is a cost ratio term and A is an equipment deterioration term. Worked costings are given to show that no one maintenance strategy is invariably the best.