LIGHT REFLECTION FROM HAIR 311 3,5 3,0 2,5 2,0 1,5 1,0 I I 0.07 0.001 I I o.12 --I-- +1.96'Std. Err. [--I +1.00*Std. Err. ß Mean black brown blonde Hair Type Figure 8. Box-and-whisker plot summarizing cuticle scale angles for the three hair types. Data points, boxes, and whiskers are defined by the arithmetic group means (Mean), the standard errors (Std. Err.), and the expectation values for the 95% confidence limits (1.96*Std. Err.). The horizontal whiskers signify a specific comparison of means (LSD test) given with the (x-value to characterize the significance of the difference. as given on the horizontal whiskers in Figure 8. Here it is shown that the cuticle angle decreased from black over brown to blonde, with all differences having relevant signifi- cance levels. The cuticle angle for the black hair (2.5 ø ) is in good agreement with literature data between 2.5 ø and 3 ø (1,4,11). The values for brown and blonde hair are appreciably lower. WIDTH OF SPECULAR PEAK AT HALF HEIGHT As can be derived from the data underlying Table I, the width of the specular peaks at half height w s shows for none of the hair types a dependence on the measurement position along the hair. Thus, no continuous influence of hair grooming, that is, from root to tip, can be detected through this parameter. This is despite the fact that the blonde hair was considerably longer (30 cm) compared to the other ones (20 cm) and changed its color from medium to light blonde from root to tip. The results are summarized for the three types of hair in Figure 9 in the form of a box- and-whisker plot. The means show some variability (see Table I), where, as analysis of variance shows, inhomogeneity is significant at the 95% level (o• = 0.02). The LSD test yields the confidence levels on which the individual differences are statistically signifi- cant (see Figure 9). On this basis, only the differences between the black hair, on the one hand, and the two other hair types, on the other, are significant at the 95% level. The overall results indicate, nevertheless, that the width of the specular peak decreases with an increase in lightness of hair color. The data for w s yield a grand mean of 9.5 + 0.35 ø (95% confidence limits see Table I). This value is higher than the value Bustard and Smith (1) determined for gold-coated or black hair (8.3 ø ) but lower than their value for brown hair (10.8ø). This indicates that the origin of the specular reflected light is largely from near the very surface of the hair, irrespective of hair color. The decrease of width with increase of lightness may be a genuine effect, related to differences in the cuticle angle distribution. The authors, at

312 JOURNAL OF COSMETIC SCIENCE 11,5 -•- 11,0 ß 10,5 --• 10,0 • 9,5 • 9,0 ß 13 8,5 8,0 I t 0,035 t t0.005 --[-- _+1.96'Std. Err. • +1.00*Std. Err. ß Mean I to.5o black brown blonde Hair Type Figure 9. Box-and-whisker plot, summarizing the values for the width of the specular peak at half height, ws, for the three hair types (see Figure 8). this stage of the investigation, would tend to assume, however, that the effect is related to a tendency of the fit algorithms to detect narrower distributions for specularly reflected light with decreasing prominence of the related peak in the GP curve. Gen- erally, the width of the specular peak for a given type of hair is a measure of the distribution of cuticle angles and can serve to assess surface damage, for a hair before and after a cosmetic treatment. LOCATION OF THE DIFFUSE REFLECTION PEAK For an ideal diffuse reflector, diffuse backward scattering would be uniform in intensity. With the strong directional component for this type of light, this condition is obviously not fulfilled for the surface of hair. The results in Table I for the different fiber types at their root ends (1 cm), where all hairs are largely undamaged, show values between 43 o and 46 ø that are not significantly different (ANOVA: o• = 0.64). The values are higher than those of the respective receptor angles for specular reflection (350-36 ø ) and even higher than that of the expected receptor angle for a fiat, specularly reflective surface (40ø). For the black, Asian hair the group means for the position of the peak location for diffuse reflection is 40 ø (see Table I). This effect is due to the fact that •/d decreases significantly from root to tip (LR: o• = 0.006 see Figure 10), paralleled by possibly a slight increase in the cuticle angle, as discussed above. There appears no straightforward explanation for this phenomenon, apart from the assumption that it is related to systematic and an- tagonistic changes of the hair surface due to grooming. For the brown hair the receptor angle for diffuse reflections remains unchanged along the hair (ANOVA: o• = 0.4), yielding a group mean of 45 ø + 1.4 ø. The apparent shift of•/o to higher angles for the blonde hair (see Figure 10) is not significant (LR: o• = 0.16), yielding the group mean of 46 ø _+ 1 ø, which is not significantly different from that for the brown hair (LSD: (x = 0.44). The 5 ø-6ø shift of the diffuse reflection peak with respect to the expectation value of 40 ø is attributed to the fact that diffuse reflection mainly occurs at various locations near the