Understanding Diamond Light: Scintillation, Dispersion, Brilliance, and Fire

The proportions of a diamond cut, the polish, and the symmetry of the stone are the three main factors that give a diamond its optimal light reflection.  The high quality of the diamond cut will produce a diamond with fire, scintillation, and a dazzling brilliance due to a high light return. When the cut is poor, the light entering the diamond may become limited or the light will seep out the sides and bottom of the gem. Poor cuts can produce diamonds that are dull and lifeless as well as appear dark, even though its clarity and color are of superior quality. Therefore, the cut is the most important factor in producing a diamond of excellent appearance.

When choosing a diamond, the highest cut grade should be of prime consideration.  The four main qualities of the diamond that are dependent on the grade of the cut are scintillation, dispersion, brilliance, and fire.

Diamond Scintillation

Scintillation refers to the intense sparkles of light or flashes produced when tilting a diamond from side to side. The light that enters a diamond may not immediately get reflected back and may reflect towards the diamond’s center from its inside walls. The light that bounces off the diamond’s internal walls is the diamond quality called scintillation. Ideally, diamonds should display lots of captivating flashes visible across the surface of the gem.

Dispersion and fire

Dispersion and fire are different but related attributes of polished diamonds.  Scientifically, dispersion refers to the break-up of white light into a spectrum of colors. In dispersion, white light separates into colors that take different paths because the amount of refraction that takes place in the material differs. Dispersion is a property inherent in transparent materials, and oftentimes a single value based on the refractive index of the materials. All polished diamonds regardless of proportions or shape, for example, have the same dispersion property.


A diamond’s brilliance is dependent upon the quality of cut which gives the diamond the ability to reflect the most amount of light. The “brilliance” of the diamond depends on good light performance, or light refraction and the return of light through the diamond’s top. As light hits the surface of the diamond, some enter the stone while some are reflected back. The crown’s angles return back the most reflected light. Diamonds that are too shallow or too deep return less light. Polishing also affects the brilliance of a diamond, so its every facet should be polished professionally right after cutting. A high level of brilliance will also be attained if the diamond is well-balanced and symmetrical with properly aligned facets.  A high-quality cut grade assigned by a gemologist means that the diamond exudes a high degree of fire and brilliance.

The fire of the diamond is the light that shoots back through the diamond’s top after it is bounced off inside its walls to its center. The resulting color spectrum is due to the slight bending of the light by the diamond. The fire of diamonds differs, depending on the stone’s cut and polish, the lighting conditions and the viewing environments. Fire is influenced by the angle of light that enters and exits the diamond and the interactions of the diamond facets with light, among others.

Fire is one of the main reasons why diamonds are desired and treasured by many people. 

This article was contributed by Frank Fisher.

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learn everything you need to know before you buy a diamond in this detailed book!

learn everything you need to know before you buy a diamond in this detailed book!