Comparison of the spectrum of a calcite crystal (polarized E^c) taken with polarizers of three different polarization efficiencies.

The apparent height of an absorption band of an anisotropic solid can be significantly decreased is polarizers of low polarization efficiency are used.  This graph compares the spectrum of calcite taken with a polarizer of  zero efficiency (red trace - unpolarized), a Au-wire-grid polarizer of moderate efficiency on a AgBr substrate; and a  LiIO₃ (Glan-Thompson design) polarizer of very high polarization efficiency (back trace).  For the stronger bands, the high efficiency polarizer produces higher absorbance values which are close to the true absorption intensity of the calcite.
 

From:  Libowitzky E, Rossman GR (1996)  Principles of quantitative absorbance measurements in anisotropic crystals.  Physics and Chemistry of Minerals 23, 319-327.