A method is disclosed for determining an illumination beam dose in surgical field illumination. Said method comprises the following steps: at least one actual illumination-relevant value is sensed； and an illumination beam dose is calculated from said sensed actual value. Sensing of the actual illumination-relevant value includes sensing of a value of at least one adjustable parameter of an illumination device. Furthermore, simulated dose characteristics associated with the adjustable parameter are selected, at least one simulated dose value is calculated taking into account the value of the adjustable parameter and the associated simulated dose characteristics, and the illumination beam dose is calculated taking into account the at least one simulated dose value. Also disclosed are an apparatus, a computer program product, and a surgical microscope for carrying out said method.
