242 JOURNAL OF COSMETIC SCIENCE artificial illumination (SERIC Co., artificial solar light XC-100AF). The evaluation was rated with scores ranging from 1 to 7 (1: no luster 7: maximum luster), and also permitted the mean values (e.g., 1.5, 2.5) of an evaluating score. Both the surface brightness, including diffuse and specular compositions Ir and the diffuse composition Id, were changed to voltage by photodiodes, respectively, and then converted into "per unit" in an irradiation part. The potential difference of these was considered as the device output. RESULTS AND DISCUSSION VERIFICATION OF DRM IN HUMAN HAIR Since the irradiation area changes during measurement by the goniophotometric method when the receiving angle becomes large, the reflectance also increases, making the change unclear. The reflectance, which is converted into "per unit" in an irradiation part, is shown in Figure 6. The reflective characteristic of human hair, which is plotted in a three-dimensional graph, is shown in Figure 7. The peak of the receiving angle direction corresponds to the reflective characteristic of a specular reflective composition. The peak of the wavelength direction corresponds to the object's color, which is explained as a characteristic of a diffuse reflective composition. The difference between the reflectance in each receiving angle and its average value is shown in Figure 8. The standard deviation is shown in Figure 9. Since the reflectance was similar at all receiving angles, 0.20 0.15 0.10 0.05 0.00 -2O receiver angle [deg] 70 ,.•Oo Figure 7. 3D view of spectral reflectance. •o o

DEVICE TO MEASURE HAIR LUSTER 243 0.10 0.05 0.00 -0.05 -0.10 400 500 600 700 wave length [nm] Figure 8. Similarities among spectral reflectances. even when the measurement angle changed, it was concluded that the spectrum com- position was invariable. From this result, the conditions not being influenced by the wavelength and geometric parameter satisfied an important assumption of DRM. There- fore, it was verified that human hair can be described by DRM. INFLUENCE OF THE ARRANGEMENT ANGLE ON REFLECTANCE The reflectance characteristics in each arrangement angle of human hair were plotted in three-dimensional graphs, as shown in Figure 10. When the arrangement angles p of the O.OOO4 = 0.0003 • 0.0002 ß -• 0.0001 0.0000 400 500 600 700 wave length [nm] Figure 9. Standard deviation of the difference between reflectance and the average value.