A fluorescent light microscope for measuring a sample comprises a light source providing transfer light having a transfer wavelength for transferring a fluorescent dye in the sample from one state into another state, and a detector which measures fluorescent light from the sample with spatial resolution. The light source comprises a laser, an optical wave guide connected to the laser, and a wavelength-selective device connected to the optical wave guide. The laser emits pump light of a pump wavelength other than the transfer wavelength and injects the pump light into the optical wave guide. The pump light, due to Raman scattering being stimulated in the optical wave guide, generates a light spectrum emerging from the optical wave guide which has, besides the pump wavelength, at least one red-shifted Stokes line whose full width at half maximum is smaller than half of its distance to its next neighbor line on the blue side of the spectrum; and the wavelength-selective device singles out the transfer light by its transfer wavelength from the red-shifted Stokes lines of the light spectrum.