Branch of spectroscopy dealing with measurement of radiant energy transmitted or reflected by a body as a function of wavelength .
The measurement is usually compared to that transmitted or reflected by a system that serves as a standard. In chemistry and physics, different types of spectrophotometers cover wide ranges of the electromagnetic spectrum : light , infrared (IR), or microwave . UV spectrophotometry is particularly useful in detecting and quantifying colourless substances in solution . IR spectrophotometry is used mostly to study the molecular structures of complex organic compounds. In astronomy and astrophysics, spectrophotometric studies also include the X-ray and {{link=gamma ray">gamma ray ranges of the spectrum. See also colorimetry .