An insight into the present capabilities of national metrology institutes for measuring sparkle

Large effect pigments, due to their strongly specular reflectance, produce a special visual texture known as sparkle. The use of these pigments in many industries (automotive, cosmetic, paper, architecture...) makes the control of this visual texture necessary. A measurement scale has to be developed, so that traceability can be provided by national metrology institutes (NMI) or designated institutes. Some of them (PTB, METAS, CMI and CSIC) have tested their existing capabilities to measure sparkle, and their results are presented. Two possible sources of systematic errors have been identified: inadequate illumination and collection full-angles, and inadequate size of the virtual aperture used to assess the luminous flux reflected on the effect pigments. The measurement scale of sparkle used in this comparison is thoroughly presented. This comparison will allow the methodology to measure sparkle to be improved.This article was written within the EMPIR 16NRM08 Project “Bidirectional reflectance definition” (BiRD). The EMPIR is jointly funded by the EMPIR participating countries within EURAMET and the European Union. The EMPIR is jointly funded by the EMPIR participating countries within EURAMET and the European Union. Part of the authors (Instituto de Óptica “Daza de Valdés”) are also grateful to Comunidad de Madrid for funding the project S2018/NMT-4326-SINFOTON2-C

An insight into the present capabilities of national metrology institutes for measuring sparkle

18 pags., 15 figs., 1 tab.Large-effect pigments, due to their strongly specular reflectance, produce a special visual texture known as sparkle. The use of these pigments in many industries (automotive, cosmetic, paper, architecture...) makes the control of this visual texture necessary. Sparkle measurands have been defined in this article, so that traceability of sparkle measurements can be provided by national metrology institutes or designated institutes. Some of them (Physikalisch-Technische Bundesanstalt, Eidgenössisches Institut für Metrologie, Cesky Metrologicky Institut and Consejo Superior de Investigaciones Científicas) have tested their existing measurement capabilities for the defined sparkle measurands, and their results are presented and thoroughly compared. Two possible sources of systematic error have been identified: inadequate illumination and collection solid angles, and an inadequate size of the virtual aperture used to assess the luminous flux reflected by the effect pigments. Finally, it has been shown that the measures correlate excellently with the sparkle visual data. The results shown in this research support the sparkle measurands defined here as adequate quantities for defining the standard measurement scale of sparkle claimed by industry.This article was written within the EMPIR 16NRM08 Project ‘Bidirectional reflectance definition’ (BiRD). The EMPIR is jointly funded by the participating countries within EURAMET and the European Union. Some of the authors (Instituto de Optica ‘Daza de Valdes’) are also grateful to Comunidad de Madrid for funding the project S2018/NMT4326-SINFOTON2-C