That sounds complicated, but isn't really. If you move a light twice as far from your subject, you end up with only one-quarter of the light on the subject.

这听起来有些复杂，其实很简单，举例说明：如果你将光源至被摄主体的距离增加1倍，那么落在主体上的光线只有距离增加前的四分之一。