Gonioreflectometer-based gloss standard calibration

摘要

Highly polished plane gloss standards are indispensable when using a glossmeter. The gloss value of a primary reference standard is defined by its refractive index at 589.3 nm. This definition allows ease of use, but the calibration accuracy is limited to about ±0.5% due to inconsistency between the monochromatic definition and the polychromatic use in the glossmeter. Detector-based radiometry has improved a lot in the last 20 years and it is now time to think about changing the primary gloss standard calibration to absolute specular reflectance-based measurements. This paper is a step into this direction. It shows a refractive index fitting method for gloss standards based on gonioreflectometric specular-reflection measurements, Fresnel's equation and least-squares fitting. The refractive index fitted data showed ±0.23% agreement on average with the gonioreflectometric data measured in 1° steps and ±0.07% agreement on average for the angular corrected data. The requirement for an uncertainty of ±0.1% in the gonioreflectometric calibration was also analysed.