Comparison of narrow-band reflectance spectroscopy and tristimulus colorimetry for measurements of skin and hair color in persons of different biological ancestry

We have used two modern computerized handheld reflectometers, the Photovolt ColorWalk colorimeter (a tristimulus colorimeter; Photovolt, UMM Electroni cs, Indianapolis, IN) and the DermaSpectrometer (a specialized narrow-band reflectometer; Cortex Technology, Hadsund, Denmark), to compare two methods for the objective determination of skin and hair color. These instruments both determine color by measuring the intensity of reflected light of parti cular wavelengths. The Photovolt ColorWalk instrument does so by shining a white light and sensing the intensity of the reflected light with a Linear photodiode array. The ColorWalk results can then be expressed in terms of s everal standard color systems, most importantly, the Commission Internation al d'Eclairage (CIE) Lab system, in which any color can be described by thr ee values: L*, the lightness; a*, the amount of green or red; and b*, the a mount of yellow or blue. Instead of a white light and photodiodes, the Derm aSpectrometer uses two light-emitting diodes (LEDs), one green and one red, to illuminate a surface, and then it records the intensity of the reflecte d light. The results of these readings are expressed in terms of erythema ( E) and melanin (M) indices. We measured the unexposed skin of the inner upp er arm, the exposed skin of the forehead, and the hair, of 80 persons using these two instruments. Since it is important for the application of these measures in anthropology that we understand their relationship across a num ber of different pigmentation levels, we sampled persons from several diffe rent groups, namely, European Americans (n = 55), African Americans (n = 9) , South Asians (n = 7), and East Asians (n = 9). In these subjects, there i s a very high correlation between L* and the M index for the inner arm (R-2 = 0.928, P < 0.001), the forehead (R-2 = 0.822, P < 0.001), and the hair ( R-2 = 0.827, P < 0.001). The relationship between a* and the E index is com plex and dependent on the pigmentation level. We conclude that while both t ypes of instruments provide accurate estimates of pigment level in skin and hair, measurements using narrow-band instruments may be less affected by t he greater redness of certain body sites due to increased vascularization. (C) 2000 Wiley-Liss, Inc.