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The paper considers lamp replacement and depreciation of lighting equipment as factors in lighting maintenance. Improved ageing characteristics and lighting service provide increased economic justification for group replacement of discharge and fluorescent lamps, and the economics and procedure are discussed. Recent investigations in this country and the United States into lighting fittings' depreciation have revealed, among other features, that ventilation of open fittings has a decisive self-cleaning effect which profoundly affects the economics of lighting maintenance and the performance of the lighting installation. A consideration of the various factors, economic and practical, involved in lighting depreciation leads to the conclusion that maintenance should be a primary factor both in lighting design and fitting design.