PHOTOVOLT TECHNICAL NOTE
Color Analysis Using The Photovolt Reflectometers

DESCRIPTION
A spreadsheet application for Microsoft Excel for Windows converts the amber, blue, and green reflectance measurements from the PHOTOVOLT MODEL 575, 670, and 577 Reflectance Meters to tristimulus color coordinate 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 THE PHOTOVOLT ANALYSIS PROGRAM

(very) Minimum System Requirements
· IBM-PC/AT (or 100% compatible)
· 640 KB Random Access Memory (RAM)
· 1 floppy disk drive (5.25" or 3.5")
· 1 hard disk (20 MB)
· Graphics adapter/monitor with 640 x 348 resolution
· Mouse type pointing device
· MS or PC Disk Operating System (DOS), Version 3.3 or later
· Microsoft Windows, Version 3.0 or later
· Microsoft Excel for Windows, Version 3.0 or later

Installation Procedure

Install the PC, DOS, Windows, and Excel according to the manufacturer's instructions. Create a directory for the blank color analysis table and completed report sheets. Copy all contents of the Color Analysis Disk to the directory using the DOS copy command or the Windows File Manager.

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

Equation                                                                              Reference

CIE - X, Y, Z Scale
X = 0.80 A + 0.18 B                             ASTM D 2244
Y = 1.00 G                                      ASTM D 2244
Z = 1.18 B                                      ASTM D 2244

CIE - x, y, z Scale
x = X/(X+Y+Z)                                   ASTM D 2244
y = Y/(X+Y+Z)                                   ASTM D 2244
z = 1- (x+y)                                    ASTM D 2244

L*a*b* (CIE 1976)
L* = 116 (Y/100)^1/3 - 16                       ASTM D 2244
a* = 500 ((X/100)^1/3 - (Y/100)^1/3)            ASTM D 2244
b* = 200 ((Y/100) ^1/3 - (Z/100)^1/3)           ASTM D 2244

L* = 116 (Y/100) ^1/3 - 16                      ASTM D 2244
u' = 4X/(X + 15Y + 3Z)                          ASTM D 2244
v' = 9Y/(X + 15Y + 3Z)                          ASTM D 2244

Simplified NBS Equation
L = 10 Y^½                                      ASTM D 2244
a = (17.5 (1.02 X-Y)) / Y^½                     ASTM D 2244
b = (7.0 (Y - 0.847 Z)) / Y^½                   ASTM D 2244

Yellowness Index
YI = 100 (A - B) / G                            ASTM E 313
YI = 128X - 106Z / Y                            ASTM D 1925
YI = 100 (1 - 0.847 Z / Y)                      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)^½ ASTM D 2244
d"E" of L a b = ((L1-L2)^2+(a1-a2)^2+(b1-b2)^2)^½ ASTM D 2244
d"C" of a* b* = ((a1*-a2*)^2+(b1*-b2*)^2)^½     ASTM D 2244
d"C" of a b = ((a1-a2)^2+(b1-b2)^2)^½           ASTM D 2244