Measuring gloss using spectral reflectance

Abstract Gloss is historically measured at three angles of incidence, 20°, 60°, and 85°, using a light source filtered to replicate Illuminant C and a colored glass filter designed to reproduce the CIE 1931 photopic luminous efficiency function. Herein an alternate method that relies on the spectral reflectance of a gloss standard and the sample, both measured with a new reference gonio-spectrometer and in accordance with the geometries specified in internationally recognized standards, is presented. The spectral reflectance measured with the aid of a spectrometer is converted to luminous flux which is then used to calculate gloss. This alternate method eliminates the errors associated with the source actual spectral power distribution vs. that of Illuminant C, and the actual spectral transmittance of the colored glass filter used vs. the spectral distribution of the photopic luminous efficiency function. Gloss measurement results for a synthetic quartz sample, Suprasil 311, are presented. The measured values averaged over three reflectance measurements are 71.3 ± 1.2 ( k = 2), 82.2 ± 0.9 ( k = 2), and 98.1 ± 3.0 ( k = 2), and these agree exceptionally well with the theoretical values of 71.3, 82.1, and 98.1 Gloss Units at 20°, 60°, and 85°, respectively. Components of uncertainty are discussed. In addition, a gloss scale is proposed. The components of the scale have been selected from readily available optical glass types for ease of fabrication and relatively low cost. They span a range from 4.4 to almost 170 Gloss Units for light at 20° angle of incidence.