spectrophotometer

n. device for measuring the relative intensity of parts of a spectrum

In physics, spectrophotometry is the quantitative study of electromagnetic spectra. It is more specific than the general term electromagnetic spectroscopy in that spectrophotometry deals with visible light, near-ultraviolet, and near-infrared. Also, the term does not cover time-resolved spectroscopic techniques.
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Spectrophotometer /spec·tro·pho·tom·e·ter/ 1. an apparatus for measuring light sense by means of a spectrum. 2. [more]Spectrophotometer - Community and Resources

Noun
1. a photometer for comparing two light radiations wavelength by wavelength
(hypernym) photometer

(n.)
An instrument for measuring or comparing the intensites of the colors of the spectrum.