Investigation On Whiteness Of Object Surface Color And Illuminant Color

LED is now widely used in indoor and outdoor lightings.Comparing with traditional lights,including tungsten and fluorescent lights,LED lights have the advantage of longer life and low energy consumption.In addition,LED lights are more adaptive.Their parameters such as colour temperature and illuminance could be adjusted to satisfy consumers,needs.With the development of LED industry,whiteness evaluation is faced with many challenges:for the surface color,it is necessary to develop a whiteness metric which can be used under various lighting environment;for the white lighting,it is necessary to establish a locus to represent LED white lighting.The first part of this project investigated whiteness metrics under different lightings.An experiment was conducted to extend the CIE whiteness metric under white sources having different CCTs and UV content.Three metrics has been tested including CIE whiteness,Ganz whiteness,Uchida whiteness.It has been demonstrated that these metrics all have bad performance under low CCT lighting.Aimed at CIE whiteness,two optimized versions were derived and they all gave similar degree of accuracy in predicting experimental data,including CAT02 method and coefficient optimization method.The one with CAT02 performed quite well and is simple to use by applying the original CIE whiteness index under D65.What's more,to investigate the tint boundary of whiteness metrics,a supplementary experiment is conducted.As a results,the old-4/+2 tint boundary cannot include all the samples which are perceived as white by observers.So a limit of±5T is proposed.The second part of this project investigated the white lighting locus.Using pair comparison method,the experiment try to find the most neutral point under different CCTs with two adaptation methods and two orders.It has been proved that the adaptation method don't have significant influence on white lighting locus,which has proved the accuracy of experiment results.Also,our results keep consistent with Ohno's to some extent that white lighting locus located below the blackbody locus.And neutral point under high CCT is closer to blackbody locus than low CCT.What's more,to investigate the most neutral point,a supplementary experiment is conducted.The result keep consistent with Smet's that the most neutral point has the 5875K CCT and-0.01 Duv.