Light performance describes how much light or brilliance is returned to the eye when a diamond is viewed from the top. Light performance makes up part of the Cut grade of a diamond by GIA and AGSL, and takes into account how much brilliance (white light), fire (spectral rainbow light) and scintillation (light bounce or movement from facet to facet within the gem) the diamond displays when viewed straight down and from side to side.
See also: brilliance, fire, scintillation, cut