Spectrometer is an optical instrument, which is used to measure the properties of light over a specific portion of the electromagnetic spectrum. Its independent variable is usually the wavelength of the light that is normally expressed as some fraction of a meter, but sometimes expressed as some unit directly proportional to the photon energy, such as wave number or electron volts. This is used in spectroscopy for producing spectral lines and measuring their wavelengths and intensities. This is applied to instruments that operate over a very wide range of wavelengths, from gamma rays and X-rays into the far infrared. They are often used in astronomy and branches of chemistry.

Spectrophotometer is a photometer (a device for measuring light intensity) that can measure intensity as a function of the color, or more specifically, the wavelength of light. There are many kinds of spectrophotometers. The important features of spectrophotometers include the spectral bandwidth and linear range. There are two major classes of spectrophotometers; single beam and double beam. A double beam spectrophotometer measures the ratio of the light intensity on two different light paths, and a single beam spectrophotometer measures the absolute light intensity.

Spectrometers are used in spectroscopic analysis to identify materials. Spectroscopes are used often in astronomy and some branches of chemistry. Early spectroscopes were simply a prism with graduations marking wavelengths of light. Modern spectroscopes, such as monochromators, generally use a diffraction grating, a movable slit, and some kind of photodetector, all automated and controlled by a computer. When a material is heated to incandescence it emits light that is characteristic of the atomic makeup of the material. Particular light frequencies give rise to sharply defined bands on the scale which can be thought of as fingerprints.

Spectrum analyzer is a device, which is used to examine the spectral composition of some electrical, acoustic, or optical waveform. There are two types of spectrum analyzers such as analog and digital spectrum analyzers. An analog spectrum analyzer uses either a variable band pass filter whose mid-frequency is automatically tuned through the range of frequencies of which the spectrum is to be measured or a super heterodyne receiver where the local oscillator is swept through a range of frequencies.