A light source configured for fluorescence diagnosis comprises a first semiconductor-illuminant based light emission unit configured to emit first light in a broadband first wavelength spectrum, a second semiconductor-illuminant based light emission unit configured to emit second light in a narrowband second wavelength spectrum for excitation of fluorescence, a spectral filter for the first light emission unit that is configured to block spectral components of the first wavelength spectrum which are assigned to a color channel of a camera the fluorescence is to be detected with, and to transmit remaining spectral components of the first wavelength spectrum, a brightness control for the first light emission unit configured to dim the intensity of the emitted first light, and an optical intensity attenuator for the first light emission unit that is configured to reduce the intensity of the emitted first light below the minimum intensity obtainable through the brightness control without the intensity attenuator.