A spectrometer is an optical instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization state.
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Spectrometer is a device for creating andf measuring spectrum. It is an instrument used to disperse radiant energy or particles into a spectrum and measure properties such as wavelength, mass, energy or index of refraction.