The key to understanding what that means lies with the term refraction, the ability of a transparent medium, like glass, water, or the eye to change the direction of light passing through it.

理解这代表什么的关键取决于这个术语折光能力，一个透明媒体的能力，如玻璃，水，或者眼睛，当光穿过它时，来改变光的方向。