The ultraviolet radiation (UV) protection efficiency of apparel dyed fabrics of cotton and polyester were evaluated by UPF (UV-B protection index) and APE (UV-A protection index) to investigate the effects of hue and lightness of the fabrics. UV transmittance of fabrics changed along with the thickness of the fabrics. The characteristic spectral transmittance of dyes appeared on the dyed taffeta (thickness : 0.1 mm), but on the dyed fabrics thicker than kanakin (thickness : 0.3 mm) they were less than 10% in all UV region. White fabrics having not enough UV protection efficiency increased their UPF and APE by dyeing and showed good protection efficiency. If the L* values of dyed fabrics were same, UPF is higher in the order of yellow, red, blue and black color. The required conditions for taffeta, thinnest fabric in this research to have enough UV protection efficiency are as follows : L* values of cellulose should be less than 25 regardless of their hue, L* values of polyester should be less than 86 in yellow, less than 67 in red and blue, less than 60 in black color, and addition to those transmittance at 370 nm should be less than 10%.

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We propose UV-A Protection Efficiency (APE) as a new valuable index of UV-A protection provided by fabrics, in addition to a UV-B protection factor UPF (Ultraviolet Protection Factor) recommended by CIE. APE was estimated by determining efficiency of apparel white fabrics in suppressing the formation of strand-breakage in plasmid DNA by sparfloxacin-photosensitization with a black light blue (BLB) lamp and solar UV-A radiation. The lower UV-A transmittance of fabrics showed the higher APE. The close inverse correlation between APE and the transmittance of fabrics at 360 nm was demonstrated with the correlation coefficient of -0.86. These findings support the validity of APE as a useful index of UV-A protection by fabrics. For practical use, APE is ranked to three grades depending on tolerated exposure time:APE from 3.5 to 4.5 is good protection, APE from 4.5 to 5.5 is very good protection, APE more than 5.5 is excellent protection. Present study also states that both APE and UPF are the important factors for protecting the ultraviolet radiation by fabrics.

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