Prediction and verification of an iridescent synthetic fiber

An optical model that predicts the reflection of light by a synthetic fiber of arbitrary cross-sectional shape is described. The model uses a Monte Carlo simulation of an exact ray trace of light for incident rays directed at a selected angle to the fiber axis. The model revealed an optical effect in round fibers that led to the prediction of a new mechanism for iridescence (change of color with angle of illumination or view) in a fabric by means of round, concentric, sheath-core fibers, with core size </=40% by volume and with the sheath and core dyed different colors. The prediction has been verified in actual fabrics.