The expression for the spectral density of polychromatic Gaussian and Gaussian-Schell model (GSM) beams propagating through double slits in Young's experiment are derived, which enables us to study the behavior of spectral switches in Young's experiment illuminated by fully and partially coherent polychromatic light beams and to judge if their spectral switches belong to the effect in singular optics. It is shown that the criterion for the effect in singular optics with polychromatic light field should be Smin=0 (Smin is the minimum of the spectral density at spectral switches) rather than Imin=0 (Imin is the minimum of the total intensity). In Young's experiment illuminated by polychromatic GSM beams the spectral switches in both near and far zones are not attributed to the effect in singular optics because Smin≠0. If the double slits in Young’s experiment are illuminated by polychromatic Gaussian beam, the spectral switches in the far zone belong to the effect in singular optics, whereas it is not the case in the near zone.