The ZytoLight system uses direct labeled FISH probes (1), eliminating the need to detect the probes with fluorophore-coupled antibodies. The probes are detected by fluorescence microscopy using appropriate filter sets (2). Due to an exciter filter (3), full-spectrum light, emitted by the microscope lamp (4), is reduced to light of a defined wavelength that specifically excites the fluorophore of the probe. This light is reflected onto the specimen by a dichroic mirror (5). The fluorophore emits light of longer wavelengths that passes the mirror. Finally, a barrier filter (6) reduces the emitted light to a defined wavelength that can be detected.