Pavilion Angle (5.09)
The original ideal pavilion angle is 40.75˚. The major gem labs do agree that slight variations from this angle will still produce a well-cut diamond. This chosen angle accommodates light traveling through the table, reflecting off the inside of the pavilion facets, bouncing to its opposite pavilion facets and leaking through the crown facets surrounding the table. As you can see in the previous illustrations the angle of incidence and angle of reflection inside the diamond creates its own angle greater than 24½˚, which will not allow the light to leak from the bottom of the stone. In the following illustration you will see that, if the pavilion angles are too steep the light will exit out of the opposite side after first reflecting once inside the diamond. The most obvious visual indication of this is the dark center in a diamond. If too flat, the light would exit the stone immediately, since the angle of incidence falls within the 24.5˚ critical angle.
