Spectrophotometers are used to determine the spectral reflectance curve of an object. The object is usually illuminated with simulated daylight. Light reflected by the object is directed to a monochromator (spectral anlyser). A diffraction grating in the monochromator separates the reflected light into individual wavelengths, typically from 360 to 700 nanometers (nm). The reflected light is measured with a photodiode array to determine the fraction of light reflected by the object (%R) ar each wavelength. The computer software will display the reflectance values in 5 or 10 steps and/or graph them as a spectral reflectance curve.

spectrophotometer analyzes light energy reflected or transmitted by a sample, wavelength by wavelength.

They measure the photometric characteristics of the material in the visible spectrum and produce spectral graphs of samples. From the spectral energy distribution of one or more illuminants (e.g. A, D65, C, CWF), tristimulus response of standard observers (2 or 10 degree) and the spectral graph of the sample, spectrophotometer calcaulates the tristimulus values for any illuminant or observer while the colorimeter can only  measure for one illuminant and one observer. In addition to the ability to supply values for quality control quite easily, the spectrophotometer is also able to determine the apperance of sample under different illuminants and calculates the metamerism.