An illumination
system (1) for
photodynamic therapy is provided, the illumination
system comprising an illumination source (2) configured to emit
electromagnetic radiation (3) to illuminate a
target surface (4) during operation, and an
electronic control unit (5), wherein the illumination source is configured such that the intensity of the
electromagnetic radiation emitted by the illumination source is variable, wherein the
electronic control unit is operably connected to the illumination source and is configured to control the operation of the illumination source in accordance with an illumination protocol during an illumination session performed with the illumination
system, and wherein the illumination protocol comprises instructions to operate the illumination source in a plurality of different
modes during the illumination session, said
modes comprising: a) a first mode, wherein in the first mode the
electronic control unit controls the operation of the illumination source such that the intensity of the
electromagnetic radiation emitted by the illumination source is continuously or quasi-continuously increased from a base intensity B to a target intensity T over a first mode time interval, b) a second mode, wherein in the second mode the electronic
control unit controls the operation of the illumination source such that the intensity of the electromagnetic
radiation emitted by the illumination source is constant or substantially constant over a second mode time interval, and c) a third mode, wherein in the third mode the electronic
control unit controls the operation of the illumination source such that the illumination source is operated such that a dark phase and an illumination phase are alternated over a third mode time interval, wherein the intensity of the electromagnetic
radiation emitted by the illumination source is lower in the dark phase than in the illumination phase, or wherein in the dark phase the illumination source does not emit electromagnetic
radiation, while in the illumination phase the illumination source emits electromagnetic radiation. Furthermore, a
computer program product and a kit for treating a
disease and a method for operating an illumination source and a method for treating a
skin disease are provided.