For example, if we are studying the composition of a powder mixture using diffuse reflectance, a suitable light source   is directed at the powder mixture and light is collected, usually with a lens, after it has scattered from the powder surface. Light entering a spectrometer first strikes a device (either a grating or interferometer) that separates light of different wavelengths to be measured.
To illustrate, when analyzing the makeup of a powdered blend using diffuse reflectance, a suitable illumination source is directed at the mixture, and light is gathered, usually via a lens, after it has scattered from the powder's surface. Light entering an analyzer first hits a device (either a grating or interferometer) that separates light of different wavelengths to be assessed.