光照长度(Day-Length)是指白昼光照的持续时间，又称日长、昼长。
温度的作用明显大于光照长度的影响；
The temperature's influence is deeper than the light length' s.
这条黑夜与白天分界线的形状随着季节的变化面变化，它代表着不同的白天时间长度和不同的阳光照射量。
The shape of this line between night and day varies with the seasons, which means different lengths of days and differing amounts of warming sunshine.
与白昼和黑夜的时间长度密切相关的是一年中的四季变化，最明显的是夏季和冬季的差别。其原因是太阳的光照和温度在同时发生作用。
Intimately connected with the length of day and night are our seasons, especially summer and winter; for together with the sun's light heat is also called forth.
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