Unlike a monochromator, polychromators outputs multiple beams over a range of wavelengths simultaneously.

seperates and transmit a narrow portion of light of particular wavelength

The basic parts of a spectrophotometer are a light source, a holder for the sample, a diffraction grating in a monochromator or a prism to separate the different wavelengths of light, and a detector.

The basic parts of a spectrophotometer are a light source, a holder for the sample, a diffraction grating in a monochromator or a prism to separate the different wavelengths of light, and a detector.

Prisms and gratings have different dispersive properties. Grating has a linear dispersion of wavelengths meaning the band on the focal plane varies linearly with the wavelength. Prisms are not linear, the shorter the wavelength the greater the dispersion. Thus, when a spectrum is being scanned, the dispersive device needs to rotates different amounts depending on whether it is prism or grating to focus light on the exit slit. If its grating, the slit width will need to be varied minimally; if it is a prism, the slit width will need larger changes as the dispersion gets greater.