Parsons P G, Neale R, Wolski P, Green A
Queensland Cancer Fund Laboratories, Brisbane.
Med J Aust. 1998 Apr 6;168(7):327-30. doi: 10.5694/j.1326-5377.1998.tb138960.x.
To determine the value of shade in protecting humans from solar ultraviolet (UV) radiation.
Measurement with photometers of protection factors for ultraviolet B radiation (UVB) and for total solar radiation for different types of trees and other structures during the summer months (1995-1997) in south-east Queensland. (The protection ratio is the ratio of the intensity of UVB or total solar radiation in direct sunlight to that in shade.)
For summer sun at midday, the mean (SD) UV protection ratio for the shade of trees (n = 65) was 4.21 (1.36) on a horizontal surface and 1.33 (0.30) on a vertical surface. In contrast, the mean (SD) protection ratio for total solar energy (primarily infrared) was much higher (12.1 [1.4]). Trees common in recreational areas in Australia (eucalypts: UV protection ratio, 3.52 [0.79]; Norfolk Island pines: UV protection ratio, 3.72 [0.98]) offered reduced protection compared with trees with more dense foliage (UV protection ratio, 5.48 [1.44]). Over a whole day, measurement of shade by trees and other structures showed that the UV protection ratio was lower in the morning and afternoon. Shade from awnings, buildings and hats gave similar results to those for trees. Both at midday and over a whole day satisfactory protection (UV protection ratio > 15) was obtained only in shade which eliminated exposure to the sky as well as to direct sunlight; for example, in thickly wooded areas and under low, widely overhanging structures.
Most forms of shade, while useful, offer people insufficient protection from solar UV. A fair-skinned person sheltering under a tree could suffer sunburn after less than one hour. There is a need for appropriate design of structural shade, use of other solar protection measures in conjunction with shade, and research on behavioural responses to shade.
确定树荫在保护人类免受太阳紫外线（UV）辐射方面的作用。
于1995 - 1997年夏季，在昆士兰州东南部，使用光度计测量不同类型树木及其他建筑结构对紫外线B辐射（UVB）和总太阳辐射的防护系数。（防护比率是指直射阳光下UVB或总太阳辐射强度与树荫下强度的比值。）
对于中午的夏日阳光，树木树荫（n = 65）在水平面上的平均（标准差）紫外线防护比率为4.21（1.36），在垂直面上为1.33（0.30）。相比之下，总太阳能（主要是红外线）的平均（标准差）防护比率要高得多（12.1 [1.4]）。澳大利亚休闲区常见的树木（桉树：紫外线防护比率，3.52 [0.79]；诺福克岛松：紫外线防护比率，3.72 [0.98]）与树叶更茂密的树木（紫外线防护比率，5.48 [1.44]）相比，防护效果较差。在一整天中，对树木和其他建筑结构的树荫测量显示，早晨和下午的紫外线防护比率较低。遮阳篷、建筑物和帽子提供的树荫与树木的效果相似。无论是中午还是一整天，只有在能消除天空直射和阳光直射的树荫下才能获得令人满意的防护（紫外线防护比率> 15）；例如，在树木茂密的地区以及低矮、宽大悬挑结构的下方。
大多数形式的树荫虽然有用，但为人们提供的免受太阳紫外线的防护不足。一个皮肤白皙的人在树下躲避不到一小时就可能晒伤。需要对结构性树荫进行合理设计，将其他防晒措施与树荫结合使用，并研究人们对树荫的行为反应。
