Retroreflective sheeting dramatically increases the visibility and conspicuity of traffic safety facilities at night. Chromaticity is an important property of retroreflective sheeting, but there are few methods and tools for measuring retroreflected chromaticity coordinates of retroreflective sheeting in China. In this paper, measurement methods are introduced and the accuracy of portable equipment is analyzed. A spectroradiometric retroreflectometer system of the National Center of Metrization for Equipments of Roads and Bridges (NCMERB) and various portable equipment of testing agencies were selected. All instruments measured the chromaticity coordinates of the same set of samples. The data of the spectroradiometric retroreflectometer system were taken as the reference values and those of portable equipment as the comparison values. The results showed that the measurement deviations of a RoadVista 932 retroreflectometer were relatively small and that it can measure retroreflected chromaticity coordinates of retroreflective sheeting. The illuminating-viewing conditions may have little effect on the retroreflected chromaticity coordinate measurement results of yellow and red retroreflective sheeting.
In a dark channel of more than 15 m, a standard A light source was used to simulate a motor vehicle's headlight, and a Nikon D750 digital camera was used as a light receiver. While the observation angle α was 0.33°, the entrance angle component β1 was −4°, the entrance angle component β2 was 0°, and the coefficients of retroreflection of the retroreflectors were measured. The entrance angle component β1 changed from −4° to 0°, and the chromaticity coordinates of retroreflectors were then measured. Experimental results show that the maximum measurement error of the coefficient of retroreflection is −2.09%, and the measured results of the chromaticity coordinates meet the national standard of retroreflective sheeting for traffic control. Obviously, the RAW data output from the camera has a linear association with the luminous flux on the surface of retroreflectors, which can be used to calculate the coefficients of retroreflection and the chromaticity coordinates.
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