Distributions of Direct, Reflected, and Diffuse Irradiance for Ocular UV Exposure at Different Solar Elevation Angles

To analyze intensities of ocular exposure to direct (E(o,dir)), reflected (E(o,refl)), and diffuse (E(o,diff)) ultraviolet (UV) irradiance at different solar elevation angles (SEAs), a rotating manikin and dual-detector spectrometer were used to monitor the intensity of ocular exposure to UV irradiation (E(o)) and ambient UV radiation (UVR) under clear skies in Sanya, China. E(o,dir) was derived as the difference between maximum and minimum measured E(o) values. E(o,refl) was converted from the value measured at a height of 160 cm. E(o,diff) was calculated as the minimum measured E(o) value minus E(o,refl). Regression curves were fitted to determine distributions of intensities and growth rates at different wavelengths and SEAs. E(o,dir) differed from ambient UVR exposure. Linear, quadratic, and linear E(o,dir) distributions were obtained in SEA ranges of 14°–30°, 30°–50°, and 50°–90°, respectively, with maximum E(o,dir) at 32°–38° SEA. Growth rates of E(o,dir) with increasing wavelength were fitted with quadratic functions in all SEA ranges. Distributions and growth rate of E(o,refl) values were fitted with quadratic functions. Maximum E(o,diff) was achieved at the same SEA for all fitted quadratic functions. Growth rate of E(o,diff) with increasing wavelength was fitted with a linear function. E(o,dir) distributions were fitted with linear or quadratic functions in different SEA ranges. All E(o,refl) and E(o,diff) distributions were fitted with quadratic functions. As SEA increased, the E(o,dir) portion of E(o) increased and then decreased; the E(o,refl) portion increased from an initial minimum; and the E(o,diff) portion first decreased and then increased. The findings may provide data supporting on construction of a mathematical model of ocular UV exposure.