Instrumental and Operational Impacts on Spectrophotometer Color Measurements
2008
Color measurements for the classing of U.S. cottons are normally performed on the Uster High Volume Instrument (HVI), which yields two color parameters specific to cotton--Rd (reflectance) and +b (yellowness). Since Rd and +b do not readily relate to other well known and globally recognized color systems (e.g., L*a*b* or CIELAB), a program was implemented to evaluate and validate the relationships of Rd and +b to a globally recognized color system (L*a*b*) and to investigate the impacts of key instrumental and operational variables on the color results. The tile and cotton fiber batt samples analyzed were measured on 7 color spectrophotometers (bench-top and portable). Strong L* reversible Rd and b* reversible +b correlations were observed on all color units, and very similar linear relationships were obtained for L* reversible Rd and b* reversible +b regardless of the bench-top unit used. Thus, the use of L*a*b* for relating globally recognized color parameters from a color spectrophotometer to the HVI's Rd and +b color parameters was validated. The primary variable that impacted the color agreement between units was the use of HVI glass in front of the sample. L* was the color parameter that was most impacted by the use of glass in the tile and cotton fiber color measurements. The use of glass leads to a "shift" in the sample's reflectance spectrum (%R). These shifts in %R, and the use of only 2 color filters in the HVI unit, lead to the observed differences in L* reversible Rd when glass is used in the measurement.
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