translation.en: Because if the tile in that shadow were in fact in shadow, and reflecting the same amount of light to your eye as the one outside the shadow, it would have to be more reflective -- just the laws of physics.
translation.zh: 为什么？因为如果在那个阴影的瓷砖 是在真的阴影中的话， 它所反射出的到你的眼睛的光 和另一个在阴影外的瓷砖反射的光将是同量 那么它应该反射出更多的光--这正是物理定理