An illumination
system (1) for
photodynamic therapy is provided, the illumination
system comprising an illumination source (2), which is configured to emit an
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 can be varied, wherein the
electronic control unit is operatively connected to the illumination source and configured to control operation of the illumination source according to an illumination protocol during an illumination session performed with the illumination
system, and wherein the illumination protocol comprises instructions to operate the illumination source during the illumination session in a plurality of different
modes, the
modes comprising: a) a first mode, wherein, in the first mode, the
electronic control unit controls operation of the illumination source such that the intensity of the
electromagnetic radiation emitted by the illumination source is increased continuously or quasi-continuously from a base intensity B to a target intensity T within a first mode time interval, b) a second mode, wherein, in the second mode, the electronic
control unit controls operation of the illumination source such that the intensity of the electromagnetic
radiation emitted by the illumination source is constant or substantially constant for a second mode time interval, and c) a third mode, wherein, in the third mode, the electronic
control unit controls operation of the illumination source such that the illumination source is operated such that darker phases and illumination phases alternate for a third mode time interval, wherein the intensity of the electromagnetic
radiation emitted by the illumination source is lower in the darker phases than in the illumination phases, or wherein, in the darker phases the illumination source does not emit electromagnetic
radiation whereas the illumination source emits electromagnetic radiation in the illumination phases. Furthermore, a
computer program product and a kit for treating a
disease are provided and a method for operating an illumination source and a method for treating a
skin disease.