The reflected light presents an angle that is equal to that of the incident light.

The design of the modern round brilliant is such that it “contains” the light that enters it as long as possible. To understand this, we must first know a little more about how light works. For those of you who play pool or billiards, angle of incidence will be easy to grasp. When an object ball rolls across the pool table striking the side cushion (with no additional influences to sway its course), it leaves the cushion at exactly the same angle that it met the cushion. The same thing happens to light when it strikes a strongly reflective surface. If a light beam hits a reflective surface, for example at 30 degrees, it ricochets off the surface at exactly the same angle, 30 degrees. In simple terms, the angle of reflection equals the angle of incidence.