DEVICE TO MEASURE HAIR LUSTER 245 0.20 0.15 • 0.10 0.05 0.00 0 ø 45 ø 90 ø -- - 180 ø 400 500 600 700 wave length [nm] Figure 11. Diffuse reflectance at each angle of hair. Next, the wavelength of the light source was examined. The same human hair sample was measured repeatedly, and the standard deviation of the specular reflective compo- sition Is was obtained. The result is shown in Figure 14. Our theory predicted that there would be no wavelength dependence of the specular reflective composition Is. However, there would be an increase in variation in the high-wavelength region. Therefore, the light sources used need to be emitting wavelengths of 600 nm or less. DEVELOPMENT OF THE MEASUREMENT DEVICE Illustrations of our new device are shown in Figure 15 and Figure 16. It measures 200 mm in length, with a width of 40 mm and a height of 25 min. Since this device contains incident light specular reflection hair Figure 12. Specular reflection at an angle of 90 degrees.

246 JOURNAL OF COSMETIC SCIENCE 0.08 0.06 0.04 0.02 0.00 -- - 1 light, 2 receivers - 2 lights, 1 receiver I I 400 500 600 700 wave length [nm] Figure 13. Diffuse reflection of human hair for each optical system. a power supply (006P dry cell battery), it can be used in a cordless system. A general- purpose light-emitting diode (LED) emitting a wavelength of 570 mm was adopted as the light source. A photodiode was used as the receiver. A structure for holding the hair sample was constructed 90 degrees toward the device (0 degrees toward the optical system), to avoid the orientation of the hair from becoming 90 degrees. Moreover, the influence of a subject's hairstyle can be avoided by miniaturizing the measurement part. In order to explain the accuracy of the measurements by this device, three subjects were measured repeatedly. The result is shown in Table I. High accuracy with a standard deviation of 1.5 or less was obtained. 0.020 0.015 0.010 0.005 0.000 400 500 600 700 wave length [nm] Figure 14. Standard deviation of specular reflection.