Diurnal variation of ocular exposure to solar ultraviolet radiation based on data from a manikin head.

Measurements were conducted at San Ya, China (18.4°N, 109.7°E, altitude 18 m) to investigate the diurnal variation of ocular exposure to ultraviolet (UV) radiation. The experimental apparatus was composed of a manikin and a dual-detector spectrometer to simultaneously measure ocular and ambient UV data. The experimental apparatus was rotated clockwise to simulate three different types of exposure. When the manikin was facing into the sun, the ocular exposure to UV radiation on a summer day was bimodally distributed. The maximum ocular UV irradiance occurred at solar elevations of around 40° and 50° for UVA and UVB respectively. The spectral irradiances were measured at specific wavelength to obtain the ocular biologically effective UV (UV(BE) ) irradiances for photokeratitis, photoconjunctivitis and cataract, and the UV index (UVI) was calculated at the same time point for comparison. When the manikin faced the sun, the maximal ocular UV(BE) irradiance values were obtained at the solar elevation where the UVI value was 8. The results of this study showed that protection against ocular overexposure during outdoor activities should be taken not only at noon but also at other times.