It means I can take two identical squares, put them in light and dark surrounds, and the one on the dark surround looks lighter than on the light surround.
这意味着我可以将这两个完全相同的正方形， 将它们放入明亮的和黑暗的环境当中， 现在这个在黑暗环境中的看起来比另一个在灯光环境下的要明亮些