Spectroscopy and Colorimetry

Colorimetry (color measurement) includes many factors such as an object's physical characteristics, the surrounding colors, the light source, and the sensor or viewer. Two spectrally different objects may be distinguishable under one light source and look the same under a different light source, making these objects a metameric pair. This difference depends on the light source and the sensitivity of the sensor or the response of the human visual system.

Common color-measurement devices are densitometers, colorimeters and spectrometers. A densitometer measures and computes how much of a known amount of light is reflected from-or transmitted through-an object. A spectrometer measures spectral data-the amount of light energy reflected from, transmitted through, or emitted from an object at several intervals along the Spectrum. These values are represented as a spectral curve. Data obtained from a spectrometer is the most complete description of a color that can be achieved. Spectral data is device and illuminant-independent, which means that lighting changes, the uniqueness of each human viewer, and various imaging components have no effect on the data. Since spectral data is not dependent on a viewer, it can describe spectra beyond the visible (380-720nm), including UV and IR radiation. Spectral data can be used to analyze and predict metamerism. Spectral data can be translated into colorimetric or densitometric data with a few calculations.