Colour differences in Caucasian and Oriental women's faces illuminated by white light-emitting diode sources

To provide an approach to facial contrast, analysing CIELAB colour differences (ΔEab,10∗) and its components in women's faces from two different ethnic groups, illuminated by modern white light-emitting diodes (LEDs) or traditional illuminants recommended by the International Commission on Illumination (CIE).

We performed spectrophotometric measurements of spectral reflectance factors on forehead and cheek of 87 young healthy women (50 Caucasians and 37 Orientals), plus five commercial red lipsticks. We considered a set of 10 white LED illuminants, representative of technologies currently available on the market, plus eight main illuminants currently recommended by the CIE, representative of conventional incandescent, daylight and fluorescent light sources. Under each of these 18 illuminants, we analysed the magnitude and components of ΔEab,10∗ between Caucasian and Oriental women (considering cheek and forehead), as well as for cheek-forehead and cheek-lipsticks in Caucasian and Oriental women. Colour-inconstancy indices for cheek, forehead and lipsticks were computed, assuming D65 and A as reference illuminants.

ΔEab,10∗ between forehead and cheek were quantitatively and qualitatively different in Orientals and Caucasians, but discrepancies with respect to average values for 18 illuminants were small (1.5% and 5.0% for Orientals and Caucasians, respectively). ΔEab,10∗ between Caucasians and Orientals were also quantitatively and qualitatively different both for forehead and cheek, and discrepancies with respect to average values were again small (1.0% and 3.9% for forehead and cheek, respectively). ΔEab,10∗ between lipsticks and cheek were at least two times higher than those between forehead and cheek. Regarding ΔEab,10∗ between lipsticks and cheeks, discrepancies with respect to average values were in the range 1.5-12.3%, although higher values of up to 54.2% were found for a white RGB LED. This white RGB LED provided the highest average colour-inconstancy indices: 17.1 and 11.5 CIELAB units, under reference illuminants D65 and A, respectively.

Colour contrasts in women's faces under CIE standard illuminants for outdoor and indoor conditions may be strongly altered using specific white LEDs. More research needs to be performed on the impact of spectral power distribution of light sources with high colour rendering indices on visual colour appearance of cosmetic products.