The lamp survival factor LSF takes into account the variation of the life of individual lamps from the mean life of the lamps. The LSF depends on the service life of the lamp. The latest data provided by the lamp manufacturers must be taken into account here. If defective lamps are replaced immediately, the lamp survival factor applied is LSF = 1. The maintenance plan for a lighting installation must also specify the optimal lamp replacement frequency. This depends on the degree of use of the lamp and is determined by analysing the period of illumination and the mean service life of the specific lamps.