The cost of a lighting installation is divided into fixed and flexible costs. The fixed costs are unrelated to the operating time of the lighting installation and comprise the annual costs for the luminaires, their installation and their cleaning. The flexible costs, on the other hand, depend on the operating time and include the electricity costs and the material and labour costs for lamp replacement. These values form the basis for the calculation of a number of features of the lighting installation. Of particular interest here are the costs accruing annually for a lighting installation. Often, however, it also makes sense in the planning phase to compare different types of lamps in terms of their efficiency. Again, these can be calculated as annual costs or as costs for the production of a specific quantity of light. When planning a new installation and specifically when improving an existing, lighting installation, it is helpful to calculate the pay-back time, i.e. the period required for the operating costs savings to offset the investment costs of the new installation.