NIST Reference Goniophotometer for Specular Gloss Measurements

The current global economy has increased international competition and the need to improve the quality of many manufactured products. Appearance measurements are used to determine the quality and acceptability of a variety of products from textiles to machine finishes. Since the manufacture and marketing of these products is international in scope, the methods, instruments, and standards for the measurement of appearance must be precise, reproducible, and internationally standardized as well. The appearance of an object is the result of a complex interaction of the light incident on the object, the optical characteristics of the object, and human perception. The scientific basis for the measurement of appearance attributes has been under investigation for the better part of a century and many appearance attributes measurements have been standardized by the Commission Internationale de l’Eclairage (CIE).1 The visual response of human observers to wavelengths of light for the spectral region of 360 to 830 nm is tabulated as the CIE standard observer. The CIE has defined a series of standard spectral distributions that are known as the CIE Standard Illuminants. Appearance attributes of an object are roughly divided into chromatic and geometric. The chromatic attributes are those that vary the spectral distribution of the reflected light (color). The geometric attributes are those that vary the spatial or angular distribution of the reflected light (gloss and haze). This paper describes the reference goniophotometer at the National Institute of Standards and Technology (NIST). This instrument complies with the geometrical and spectral conditions specified by the American Society for Testing and Materials (ASTM) D 5232 and the International Organization for Standardization (ISO) 28133 documentary standards for the measurement of specular gloss of nonmetallic surfaces at fixed specular geometries of 20, 60, and 85°. Gloss measurements for other industrial applications using different geometries can also be accommodated. This goniophotometer is also capable of characterizing the distribution of unabsorbed incident radiation by NIST Reference Goniophotometer for Specular Gloss Measurements