When you shine a flashlight on an egg-faced ruby, there will be two or three intersecting lights on the surface of the ruby, sometimes even six. When the light source moves, the light on the surface of the gem will also move with it. In gemmology, this phenomenon is called the starlight effect of gems.

The definition of starlight effect in the Bible and systematic gemmology in the field of gemmology in China is that under the irradiation of parallel light, two or more intersecting bright lines appear on the surface of some cut and polished jewels and jade, which is called starlight effect. Each bright band is called a star line, and there are usually two, three or six more stars. It can be called four-shot (or cross), six-shot star line or twelve-shot starlight respectively.