光的衰减与形体

Fall-Off作者：James Gurney翻译： DylanZhang( )The brightness of any point-source illumination diminishes rapidly with distance. This weakening of light is called fall-off.It diminishes according to the inverse square law, which states that the effect of a light shining on a surface weakens at a rate comparable to the square of the distance between source and surface. 光的衰减遵循负二次方定律，(下面的长句拗口了，不过大家懂的)As the diagram above demonstrates, at twice the distance, the light is only one fourth as bright because the same rays must cover four times the area. At three times the distance, it drops to one ninth as bright.如上图所示，距离光源距离加倍后，因为光线要覆盖四倍的区域，所以单位受光只有四分之 一。

当距离变为 3 倍后，亮度衰减为九分之一译者：原帖的讨论中，有老外表示不解，其实就是日光不遵循这个原理因为太阳离地球的 距离，所以这种衰减可以忽略不记还有老外谈到激光，但是记住，激光不是点光源，激光 的光线是平行束，能量耗散少熟悉 3d 的同学对 point light 应该更容易理解所以一些类 似于点光源的光源（比如条形的日光灯管）也只是大约遵循这个定律下方是一些拥有不同衰减曲线的灯光在 3d 软件中可以更精准地控制None LinearStep Inverse ClampedInverse Square Limited。