A projection exposure system and a method for operating a projection exposure system for microlithography with an illumination system are disclosed. The illumination system includes at least one variably adjustable pupil-defining element. The illumination stress of at least one optical element of the projection exposure system is determined automatically in the case of an adjustment of the at least one variably adjustable pupil-defining element. From the automatically determined illumination stress, the maximum radiant power of the light source is set or determined and/or in which an illumination system is provided with which different illumination settings can be made. Usage of the projection exposure system is recorded and, from the history of the usage, at least one state parameter of at least one optical element of the projection exposure system is determined.