An absorption line at 900 nm has been observed in Perspex. Samples of 1 and 2 cm thickness were used and the integrated absorption (line width times peak absorption) of the line was proportionate to the thickness. Facilities for lowering the sample temperature were not available and therefore both measurements were carried out at room temperature. A Red Tide spectrophotometer was used to measure this absorption. According to the Optics Group at National Institute of Standards and Technology, USA, the line can be assigned to the "3rd overtone CH stretch of the methyl and methylene group." The present result was compared with historic data for boron impurities in indium phosphide to demonstrate the versatility of this form of spectroscopy.