spectrometer

A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum. The variable measured is most often the light's intensity but could also, for instance, be the polarization state. The independent variable is usually the wavelength of the light. A spectrometer is used in spectroscopy for producing spectral lines and measuring their wavelengths and intensities.In general, any particular instrument will operate over a small portion of this total range because of the different techniques used to measure different portions of the spectrum. Below optical frequencies (that is, at microwave and radio frequencies), the spectrum analyzer is a closely related electronic device[1].

References
1.http://en.wikipedia.org/wiki/Spectrometer