What does 'unplanned light leakage' imply about a gemstone?

'Unplanned light leakage' indicates that light is exiting the gemstone through the pavilion in an uncontrolled manner due to issues with the proportions of the cut. This typically happens when the angles or facets of the stone do not interact with light as intended, leading to a loss of brilliance and the potential for the gemstone to appear dull or lifeless. Properly proportioned gems are designed to maximize light entry and reflection, but when those proportions are off, the gem fails to retain light effectively, resulting in unwanted leakage. This characteristic directly affects the visual performance and overall appearance of the gemstone, making it less desirable.