A space for conducting photodynamic therapy (PDT) for treatment of skin diseases, especially for treatment of superficial skin tumors such as actinic keratoses, basal cell carcinomas, and initial carcinomas, wherein an active ingredient is applied to a skin area to be treated in order to form porphyrins and irradiation with light is conducted to form singlet oxygen based on the porphyrins in order to destroy diseased skin cells, wherein the space has side walls, a ceiling, and a floor, as well as at least two lighting fixtures, which are separated from one another by at least 50 cm and illuminate at least a subregion of the space, wherein there is an illuminance of at least 8,000 lux at every point in the subregion and the subregion has horizontal dimensions of at least 1 m2 and a vertical height of at least 40 cm. This invention also relates to a luminous ceiling system and method for conducting PDT.