Optical absorption properties of Au nanoparticle crystals are studied in the near infrared-to-near ultraviolet region. Although sparsely deposited Au nanoparticles show a small absorption peak at 2.4 eV, the Au nanoparticle crystals show a significantly stronger peak at 1.9 eV. Altering the temperature from room temperature to 77 K brings about very little difference in the intensity and width of the absorption peak. A qualitative model of the electronic polarizability is introduced to explain the observed peak shift as a result of assembling the nanoparticles into the 3D lattices.