1' . ASUR E OF HAIR LUSTER B C l�igul'e I. �potlighted tresses of black Asian (A) and brown (B) an under a light microscope at au initial :.ox magnification. 83

84 JOURNAL OF COSMETIC SCIENCE DERIVING A MEASURE FOR HAIR LUSTER MEASUREMENT AND ANALYSIS OF LIGHT REFLECTANCE FROM HUMAN HAIR The measurement of light reflectance from single human hairs, as described in detail in Part 1 of this paper (1), is based on the determination of the angle-dependent intensity of the light from a green laser (A- = 532 nm) scattered from a single fiber. The wave length was chosen such as to be in that range where the daylight sensitivity of the human eye is at its maximum. The basis for the investigation was three types of hair, namely black Asian and brown and blonde Caucasian hair (see Figure 1). Each sample was taken from the head of a female volunteer and exceeded in all cases 20 cm in length. The hairs were shampooed (LES 15%, pH 5.5), rinsed, dried, and stored under ambient conditions until measure­ ment. The experimental setup (1) is such that the vertically polarized laser beam (approx. 50 µW) meets the hair fiber, arranged horizontally under slight tension and in ambient, though stable, room conditions (approx. 22°C, 50% RH), at an incident angle of 40° (beam spot diameter 100 µm). The detection of the reflected light is conducted within about 100 ms in the horizontal plane containing the fiber and the incident light beam through a range of 6.5° to 173.5° with an Optical Multi-Channel Analyzer. The solid line in Figure 2 shows the so-called goniophotometric (GP) curve, derived by smoothing the angular light intensity data for the most general case, namely light 0,4 § 0,3 .c .!!!. 0 2 � ::= tn C S 0,1 C - * . .. . -!• ... - . .. . . . .. 'I .. - ... I ... ..., , ... ,.. ... ' , , :vi' 40 50 60 O,OL--------=--�•• ----�Jt..-.---- 0 10 20 30 Receptor Angle [°] ... ' ... 70 80 90 Figure 2. GP curve data(--) for a light blonde hair measured at a position near the tip end. Gaussian distributions for specularly (■■■■), diffusely (---), and internally (--) reflected light, as fitted to the GP curve (see Figure 7 in ref. 1).