Ultraviolet-Visible spectroscopy is a type of spectroscopy that uses the visible and UV portion of the electromagnetic spectrum. In this region molecules undergo electronic transitions. To obtain an absorption spectrum, a sample is placed in the spectrophotometer where ultraviolet and visible light are shined through the sample. The spectrophotometer measures how much of the light is absorbed by the sample. The intensity of light before passing through the sample is I0. The intensity of light remaining after it has passed through the sample is I. The fraction of light transmittance is (I / I0), which is usually expressed as a percent Transmittance (%T).