中间天空是由似晴天空和似阴天空组成的

作者在文中提出,除下雨等一般需要人工照明的特殊天气现象外,根据云量,天空和日光状况或云量和天空亮度分布,将天空划分为晴天空、似晴天空、似阴天空和阴天空四类。在区分天空类型时,不宜仅从云量出发,认为除了晴天空和阴天空外,其余的天空状态仅属于同一种天空类型。从多年统计平均观点来看,当太阳面被云遮挡时,天空亮度分布类似于阴天空亮度分布;当太阳面上无云时,天空亮度分布却类似于晴天空亮度分布.这两类天空的亮度分布是极不相同的:在似晴天空时,天空亮度在太阳附近处最大;在似阴天空时,从多年统计平均观点看,天空亮度最大值不会出现在太阳位置附近.此外,在似晴天空和似阴天空条件下,对于大部分地区来说,在地平面上的天空散射光照度差异也是很显著的。所以对似睛天空和似阴天空这两类天空分别加以研究是合理的。

THE INTERMEDIATE SKY IS COMPOSED OF THE PSEUDO-CLEAR SKY AND THE PSEUDO-OVERCAST SKY

This paper suggests that the actual sky,with the exception of a few par-ticular weather conditions,such as rain and snowstorm in which artificial lighting is needed.The sky can bc divided into four types according to their sunlight conditions and sky luminance distrbutions,they arc clear sky,pscudc-clear sky,pseudo-overcast sky and overcast sky.It is inadequate to classify sky merely from cloudage and to affirm that all sky conditions except clear and overcast belong to only one type.From the viewpoint of statis-tical average over many years,when sun disk is covered with cloud,luminance distribution of the sky resembles that of overcast sky,and when there is no cloud over sun disk,it is sim-ilar to that of clear sky.The luminance distributions of pscudo-clear sky and pseudo-over-cast sky are quite.In pseudo-overcatssky,the maximum skydifferent.In pseudo-clear sky,it gets maximum sky luminence can not appear in the region around the sun in considera-tion of the problem from the viewpoint of statistial average over many years.Furthermore,the differences of horizont.al diffuse illuminancc between pseudo-clear and pseudl-ouercast sky are obvious.Therefore it is more suitable to study all kinds of skies,that is pseudo-clear and pseudo-overcast sky.