| At present,the vehicle headlight sources have gradually transited from a halogen lamp to a xenon lamp,an LED,or other light sources,and a plurality of vehicle light sources coexist in actual transportation.As the most cost-effective support facility for transportation security,traffic signs are mainly based on the retroreflective properties of materials.Because the emission spectra of different light sources have obvious differences,the retroreflective properties of materials determine the spectral difference of the light sources,which could significantly affect the retroreflective materials.However,the optical parameter test system and standard regulations of the retroreflective materials have not been updated with the development of light sources,which has an impact on visibility of drivers.Therefore,through test and analysis of the spectrum of vehicle light sources and the spectral reflectance curve of retroreflective materials,this study obtained a convenient and suitable method for analyzing retroreflection coefficient and chromaticity index to modify the results of different incident light sources using traditional test equipment.Under the premise of meeting the standard methods and the application and development of vehicle light source,this study provided a theoretical foundation and experimental evidence for the development of a retroreflection coefficient measuring instrument suitable for a variety of vehicle light sources.(1)In this paper,the emission spectra of halogen light,xenon lamp and 3109 K,4148 K,5558 K,6427 K LED light source were studied.We measured the reflectance spectra of five color reflective materials of white,yellow,red,green and blue of ?,?,?,? and ?,and we used spectral fitting to obtain the reflection spectra of different color reflective film materials under different light sources.Since the spectrum of the halogen lamp was the most similar to the standard A light source,the halogen lamp was selected as the baseline,and the correction factors of retroreflection coefficients under different light sources were obtained based on the reflection spectrum of different light sources.The chromaticity coordinates of different color reflective film materials under different light sources were calculated.It can be seen from the chromaticity diagrams that the halogen lamp and the low color temperature LED caused all colors to be red-shifted,and the xenon lamp caused all colors to be blue-shifted.(2)In the second part of this paper,the direct reflection method was used to study the material's retroreflection coefficients.The light source was divided into two groups,i.e.different light source group and different color temperature LED group.The first group included a halogen lamp,a xenon lamp and an LED lamp.The results showed that the retroreflective coefficient of the white retroreflective material remained substantially stable and was minimally affected by the light source;under the illumination of the xenon lamp,the retroreflective coefficients of the yellow and red retroreflective materials were relatively small,and the green and blue retroreflective coefficients were relatively low,while the halogen lamps showed oppositely.The second group consisted of 3109 K,4148 K,6527 K LED light sources.The results showed that the yellow and red retroreflective materials were affected by the color temperature of the LED,which had a negative association with the retroreflection coefficient;the green and blue retroreflective materials were also affected by the color temperature,but the impacts were opposite.Both sets of experiments showed that as the incident angle of light source increases,the coefficient of retroreflection gradually decreases.At the same time,the brightness contrast negative of traffic signals with different colors under different light sources were analyzed,and we found that the halogen light source had the greatest influence on different traffic signs. |
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