# Color Analysis Using Photovolt Reflectometers

description: A spreadsheet application for Microsoft Excel, “PVI Color Conversion”  converts the amber, blue, and green reflectance measurements from the PHOTOVOLT MODEL 577 Reflectance Meters to CIE XYZ and to L*a*b* values. Values for yellowness, whiteness, total color difference (Delta “E”), and delta chromaticity (Delta “C”) are also calculated. A single report or a group format is available. A PHOTOVOLT “T” or “Y” search unit must be used and each unit must be equipped with tristimulus filters to measure amber, blue, and green percent reflectance. installation of analysis program: • Microsoft Excel for Windows, Version 3.0 or later color coordinate formulas : ABG% • A = Percent reflectance value with the AMBER tristimulus filter • B = Percent reflectance value with the BLUE tristimulus filter • G = Percent reflectance value with the GREEN tristiumuus filter
 CIE – X, Y, Z Scale X = 0.80 A + 0.18 B Y = 1.00 G Z = 1.18 B ASTM D 2244 ASTM D 2244 ASTM D 2244 L*a*b* (CIE 1976) L* = 116 (Y/100)^1/3 – 16 a* = 500 ((X/100)^1/3 – (Y/100)^1/3) b* = 200 ((Y/100) ^1/3 – (Z/100)^1/3) ASTM D 2244 ASTM D 2244 ASTM D 2244 L* = 116 (Y/100) ^1/3 – 16 u’ = 4X/(X + 15Y + 3Z) v’ = 9Y/(X + 15Y + 3Z) ASTM D 2244 ASTM D 2244 ASTM D 2244 Simplified NBS Equation L = 10 Y^½ a = (17.5 (1.02 X-Y)) / Y^½ b = (7.0 (Y – 0.847 Z)) / Y^½ ASTM D 2244 ASTM D 2244 ASTM D 2244 Yellowness Index YI = 100 (A – B) / G YI = 128X – 106Z / Y YI = 100 (1 – 0.847 Z / Y) ASTM E 313 ASTM D 1925 ASTM E 313 Whiteness Index WI = 4 B – 3 G ASTM E 313 Delta Values d”E” of L*a*b** = ((L1*-L2*)^2+(a1*-a2*)^2+(b1*-b2*)^2)^½d”E” of L a b = ((L1-L2)^2+(a1-a2)^2+(b1-b2)^2)^½ d”C” of a* b* = ((a1*-a2*)^2+(b1*-b2*)^2)^½ d”C” of a b = ((a1-a2)^2+(b1-b2)^2)^½ ASTM D 2244ASTM D 2244 ASTM D 2244 ASTM D 2244