dark and light spots
1. As the electron beam goes across the face of the picture tube, there are various little spots of light and dark.
当电子束扫过显象管屏幕时，屏幕上就有许多小亮点和暗点。
2. The Half - wave Lose of Light and the Central Dark Spots of the Newton's Ring
重新认识光的半波损失及牛顿环中心暗斑