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j. Cosmet. sci., 54, 301-316 (May/June 2003) Analyzing the laser-light reflection from human hair fibers. I. Light components underlying the goniophotometric curves and fiber cuticle angles F.-J. WORTMANN, DWI, Deutsches Wollforschungsinstitut e. V., Vdtmanplatz 8, 52062 Aachen, Germany, E. SCHULZE zuR WIESCHE, Henkel KGaA, Henkdstrasse 67, 40191 Diissddorf Germany, and A. BIERBAUM, Fiantec GmbH, Technologiezentrum, Europaplatz, 52068 Aachen, Germany. Accepted for publication August 1, 2002. Synopsis The consumer may repeatedly over the day apply intensive grooming procedures to maintain and improve hair appearance. Among these, brushing and combing are responsible for changes if not damage to the hair fiber surface. Beneficial or unfavorable changes to the hair surface may furthermore result from any cosmetic treatment. The analysis of laser-light reflection and scattering of human hair fibers is a direct, quick, and non-destructive method to monitor such surface changes. The application of a laser-based, multichannel goniophotometer is described, by which this analysis is based on the determination of the complete angular distribution of reflected light within a sub-second time interval. Systematic investigations of hairs differing in ethnic origin and color show that the goniophotometric curves can be analyzed by assuming three fractions of reflected light, namely, specularly, diffusely, and internally reflected light. Prominent effects are related to changes of the relative intensities of the different light fractions with hair color. The angular intensity distribution for each of the light fractions is well described by a Gaussian distribution. The angular positions of the peaks and their widths are analyzed. From the systematic shift of the intensity peak for specularly reflected light from its expectation angle, the tilt angle of the cuticle cells on the hair fiber surface is determined. All results are discussed with respect to changes along the hair length and for color differences. INTRODUCTION The consumer may repeatedly over the day apply intensive grooming procedures to maintain and improve hair appearance. Among these, brushing and combing are re- sponsible for changes if not damage to the hair fiber surface. Changes to the hair surface will furthermore result from any procedure carried out on the hair, be it bleaching, weathering, abrasion, permanent-waving, to give just a few examples. The analysis of Address all correspondence to F.-J Wortmann. 301