The light from the source is agreed on, for example, through the Mono code, acts in rame, distribution of light released by wavelength, to fall to the measuring machine.
Light from the source to fall on the sample and then through a Mono chromate, which serves to spread out the various wavelengths of light to go off the detector.
Light from the source is OK on the sample through the monochromator, which will act in the scattered light based on the various wavelengths to fall. Detector.