A prism or diffraction grating can be used to disperse the light.
Unlike a monochromator, it outputs multiple beams over a range of wavelengths simultaneously.
Polychromators have multiple exit slits, each of which allows a different wavelength to pass through it.
Instead, they use a single spatially selective detector (such as photographic film or a charge-coupled device).
Spectrographs are generally used to observe a continuous range of wavelengths, while polychromators are more commonly used to observe several discrete wavelengths, leaving gaps in-between.