The diamond spark is only something that can be observed in special conditions and is a visualization of light from a diamond that you normally cannot see.
This makes it possible to visualize light coming from all directions.

The face-up appearance of a polished diamond is often described in terms of its brilliancy (internal and external reflections of "white" light seen in a polished diamond), fire (the light dispersed into spectral colors in a polished diamond), and scintillation (the light seen in a polished diamond when viewed face-up that flash as the diamond, observer, or light source moves). Diamond Spark makes it possible to also see the symmetry of light (equal distribution of light that reflects from a diamond) and how the light expands (the angular spread of reflected light) which have an effect on the beauty of a diamond's luster.
The diamond spark created from its scintillation, brilliancy and dispersion are incredibly unique.

CGL’s (Central Gem Laboratory’s) unique Diamond Spark Report enables you to observe the beauty of these elements that make up the luster of a diamond.