An illumination device includes a light source unit and a filter wheel. The filter surface of the filter wheel includes a first surface segment and a second surface segment arranged behind the first surface segment in the direction of rotation. When the filter surface is rotated, the first and second surface segments successively extend into the illumination beam path. The first surface segment transmits only a first part of the spectrum of the emitted light and the second surface segment transmits only a different second part of the emitted light. The control unit controls the light source unit and drives the filter wheel so the light with the different spectra is emitted sequentially in time for a predetermined partial illumination duration. During the partial illumination duration of the emitted light with the first spectrum, the first or second surface segment extends into the illumination beam path.