Ou-Yang Hao, Shyr Thomas
Johnson and Johnson Consumer Inc., Skillman, NJ 08558, USA.
Photochem Photobiol Sci. 2017 Oct 11;16(10):1537-1545. doi: 10.1039/c7pp00214a.
Solar protection is an important public health issue because solar UV exposure can cause acute and chronic damage to the skin. Seeking shade is a convenient and commonly practiced sun avoidance measure. Shade works by physically shielding the skin from direct UV rays; however UV rays can also reach the skin from other angles. It is not clear how protective the widely-used shade structures like umbrellas and walls are under actual use conditions. In this study, a sky view model was applied to systematically assess the influence of different factors to umbrellas and walls, including the transmission of the shade materials, the reflectivity of the ground or the wall, diffused UV to total UV irradiance ratios, shade geometry, a person's positions and orientations in the shade. We measured the sunburn protection factor (SPF) with a calibrated UV meter at different positions in the shades of an umbrella at different times of the day and compared the measurement results with the modeling. We found that shade structures like umbrellas and walls are more effective when the ratios of diffused UV to total UV irradiance are smaller (mid-day). The effectiveness increases with more coverage, less surface reflectance, and more centralized positions in the shade. The SPF value for a typical umbrella is probably between 3 and 7 in real-life. The low sun protection level offered by a typical shade highlights the importance of educating the public about how to properly protect the skin from the sun and the importance of applying a combination of sun protection measures during extended sun exposures.
防晒是一个重要的公共卫生问题，因为太阳紫外线照射会对皮肤造成急性和慢性损伤。寻找阴凉处是一种方便且常用的防晒措施。阴凉处通过物理方式遮挡皮肤免受直射紫外线的伤害；然而，紫外线也可以从其他角度照射到皮肤。目前尚不清楚像雨伞和墙壁这样广泛使用的遮阳结构在实际使用条件下的防护效果如何。在本研究中，应用了一种天空视角模型来系统评估不同因素对雨伞和墙壁的影响，包括遮阳材料的透射率、地面或墙壁的反射率、漫射紫外线与总紫外线辐照度的比率、遮阳几何形状、人在阴凉处的位置和方向。我们在一天中的不同时间，使用校准后的紫外线计在雨伞阴凉处的不同位置测量晒伤防护系数（SPF），并将测量结果与模型进行比较。我们发现，当漫射紫外线与总紫外线辐照度的比率较小时（中午），像雨伞和墙壁这样的遮阳结构效果更好。遮阳面积越大、表面反射率越低以及在阴凉处的位置越集中，防护效果越好。在实际生活中，一把典型雨伞的SPF值可能在3到7之间。典型遮阳结构提供的低防晒水平凸显了教育公众如何正确保护皮肤免受阳光伤害的重要性，以及在长时间暴露于阳光下时采取多种防晒措施组合的重要性。
