Spectrophotometry
ØSpectrophotometer -  an instrument that measures the amount
of light absorbed, or the intensity of color at a given
wavelength. 

ØThe intensity of color can be given a numerical value by
comparing the amount of light prior to passing it through
the sample and after passing through the sample. 

ØThese quantitative measurements of light absorbed are the
Transmittance and the Absorbance.