A spectrometer (spectrograph or spectroscope)'s 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's most often the light's intensity but could also, for instance, be the polarization state. The independent variable's usually the wavelength of the light, normally expressed in nanometers, but sometimes expressed as a unit directly proportional to t… (More on Spectroscope)