Open AccessDistributions of Direct, Reflected, and Diffuse Irradiance for Ocular UV Exposure at Different Solar Elevation Angles
Author(s) -
J. Yu,
Hui Hua,
Yan Liu
Publication year - 2016
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0166729
Subject(s) - irradiance , elevation (ballistics) , optics , solar irradiance , elevation angle , sunlight , environmental science , physics , remote sensing , atmospheric sciences , astronomy , geology , azimuth
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.