A microscope and a method for illuminating an object to be imaged by a microscope are described. The method includes illuminating the object by primary light of a first spectral intensity distribution and by secondary light of a second spectral intensity distribution, the secondary light arising from the scattering of the primary light; measuring the intensity of at least one wavelength of the secondary light; comparing at least one of the measured intensity and a value derived from this measured intensity to a threshold value; and generating a signal indicating a change in the spectral intensity distribution of the secondary light by indicating whether the at least one of the measured intensity and value derived from this measured intensity either exceed or stay below the predefined threshold value.