Based on the transmittance spectra modeling, spectroscopic methods were developed to determine the optical properties of a liquid paraffin-filled double glazing unit, including reflectance and absorptance. The transmittance spectrograms of paraffin-filled double glazing units at normal incidence with different thicknesses in the wavelength 240-900 nm were measured by a TU-19 FOR spectrometer. These values were introduced into spectroscopic methods to calculate the reflectance and absorptance of paraffin-filled double glazing units. The results showed the transmittances of glazing unit that are filled with paraffin in most area are enhanced compared with the empty glazing unit. The absorption and reflectance profiles with different paraffin thicknesses are very similar in shape and are relevantly affected by the paraffin thickness. (C) 2015 Elsevier B.V. All rights reserved.