Analytic parallel-polarized light imaging technique using various light-emitting diodes: a comparison with skin conductance values. 
The quantitative difference of the light reflected from a skin surface can be analyzed using parallel-polarized light (PPL) photography when combined with an analytic technique similar to colorimetric photography.  To improve the PPL photography technique as an assessment tool for the evaluation of skin condition using light-emitting diodes (LED) of different colors.  Parallel-polarized light images were taken using white and green LED illuminators.  The acquired images were transformed to CIELAB coordinates.  An in-house skin conductance meter was constructed to assess skin hydration level.  A dermatologist evaluated the clinical grading of dryness and glossiness.  These clinical severities were also compared statistically with the CIELAB values.  As with the green illuminator, the correlation analysis of whole sites showed that the L* value positively correlated with age (r = 0.18677, P < 0.05), and that the a* value has negative and positive relationships with age (r = -0.20528, P < 0.05) and glossiness (r = 0.20885, P < 0.05) respectively.  The correlations between CIELAB values and multiple characteristics of skin were more significant when green LED was applied than when white light was applied.  In addition, coherent relationships between the grade of dryness and skin conductance values showed that visual assessment could be appropriate for the study as with objective measurement.