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

PLoS One. 2016 Nov 15;11(11):e0166729. doi: 10.1371/journal.pone.0166729. eCollection 2016.

Abstract

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

MeSH terms

  • China
  • Eye / physiopathology
  • Eye / radiation effects*
  • Humans
  • Manikins
  • Models, Theoretical*
  • Sunlight / adverse effects*
  • Ultraviolet Rays / adverse effects*

Grants and funding

This work was supported by the National Natural Science Foundation of China, Grant NO:81273034 (https://isisn.nsfc.gov.cn/egrantindex/funcindex/prjsearch-list) to YL and the Natural Science Foundation of Liaoning Province, China, Grant No: 2014021009 (http://kjjh.lninfo.gov.cn/) to JMY. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.