Visual vs. Instrumental Evaluation of Fabric Whiteness

An evaluation was made of the ability of trained observers to visually detect small uniform differences in fabric-reflectance values. Three white 50% polyester/50% cotton broadcloth fabrics, one with no finish, one with a durable-press finish, and one with a flame-retardant finish, were soiled and laundered under varying conditions. Fabric-reflectance values were determined using a reflectometer. Trained observers were then asked to visually rank specimens that differed from each other in small uniform increments of reflectance. Significant rank-order correlation coefficients indicated that the observers were able to discern differences as small as 1.0 ± 0.1 reflectance unit. This translates to detectable differences of 1.1% in soil pickup and 3.5% in soil removal.