How Light Affects Diamond Appearance

The visual appearance of a faceted diamond is impacted by a number of factors. This tiny system of mirrors is designed to gather light, reflect and refract light internally, and return that light to the eye of an observer in a scintillating display of fire and brilliance. The extent to which a given diamond is able to accomplish this is largely dependent on its cut craftsmanship. But diamond appearance is also a function of the lighting environment and the colors and shadows in the immediate physical environment. A diamond is constantly scanning the hemisphere above its crown and returning to the eye the kaleidoscope of reflections that it sees. It is also separating white light into its color components and generating individual colored sparkles in addition to flashes of white light.

A diamond cannot sparkle in a completely dark room. It needs at least some light. A well cut diamond is capable of making the most of whatever light it finds.

Without light a diamond is just a very rare and hard object. With light, even a rough diamond crystal can have a distinctly attractive luster. But it is when cut and polished that the full beauty of a diamond is revealed. And it is the quality of the cut that determines how well and how fully a diamond harnesses the beauty of the aspects of light. The best diamonds are brilliant, fiery, and scintillating.

A diamond’s light performance is a combination of related but distinct optical properties. And they can be present in different amounts. When we think of things that are brilliant a diamond comes immediately to mind. Why not a big mirror or a giant spotlight? Because those things don’t sparkle! Brilliance is a dynamic aspect - for something to sparkle change is required. In the case of a diamond it is the on/off pattern of reflections as facets go from bright to dark. For a diamond to appear brilliant and to sparkle there must be movement of the diamond, the light source or the observer.

For a diamond to be fiery, there must be dispersion of white light into its spectral colors. This happens in a diamond through refraction. White light is separated into the individual wavelengths that result in colored sparkles as it exits the crown. For a diamond to have great fire potential, the angles of the crown are critical. Built-up crowns tend to be better in this respect while shallow crowns tend to be deficient in fire. To see fire in a diamond, the lighting environment also must be conducive.

As discussed above diamonds react to the world around them, and the lighting environment is key to optimal performance. For one thing, a diamond will reflect the color of the light source or the color “temperature”. In a cooler light, like daylight or daylight equivalent, a diamond will appear whiter than in a warmer light such as from an incandescent light source or candle light.

Diamonds react very differently to diffuse light environments than they do when the light is directional. Diffuse light tends to fill in all the diamond’s facets accentuating its brightness, but may suppress fire. Directional light tends to increase contrast and some diamonds can look dark in such light, especially if the light source is large. In directional lighting with many small bright sources, such as a bank of LED lights, diamonds often come alive with white and colored sparkles (fire).

The physics of light is immutable. Light travels at fixed speeds through different materials and is refracted or “bent” to varying degrees. This has significant implications for the angles of the facets to be able not only to capture the light and return it to the eye, but also for the amount of fire (colored sparkles) the diamond is able to produce in fire- friendly light environments. Thus, overall proportions and specific facet angles are absolutely crucial. Diamonds that are cut with precision within narrow ranges of proportions and facet angles, optimize light performance by enabling the diamond to maximum combinations of brightness, fire and scintillation. Cutting faults result in light performance deficiencies such as light leakage, too much or too little contrast, or diminished fire.

Cut also matters for the diamond’s “flavor”. Certain facet arrangements can produce more and smaller virtual facets (VFs), while others produce fewer and larger. Virtual facets are the actual reflections we see which are more numerous than the physical facets on the diamond. Many fancy shape (non-round) diamonds feature very tiny VFs that result in a subtle twinkling effect often described as “crushed ice”. Early style diamond cuts feature large physical facets and a “chunkier” flavor of light performance with fewer but bolder flashes of light. Modern round brilliant tend to have a blend of large and small VFs while fancy shapes cut in a brilliant or modified brilliant style tend to have areas of both large and small to very small VFs. This variability makes fancy shapes the most challenging to assign cut grades to, but also allows for a greater range of taste.

A diamond is basically a system of mirrors composed of facets and producing ‘virtual’ facets. Virtual facets are the reflections we actually see, which are far more numerous than the physical facets on the diamond due to the fact that a single facet can reflect light rays from multiple directions. As the diamond scans the hemisphere above it, the light it finds is that which is in the environment. Where it finds a bright source it returns a bright flash, where it finds light reflected off surfaces such as clothing or walls it mirrors them back to the eye. The color temperature and intensity of actual light sources it finds will also influence the brightness and color it returns to the eye. A yellow or beige room combined with warm white light would intensify the yellowish appearance of a diamond.

The body color of the diamond itself has an effect on what we see as well. Color is perceived because certain wavelengths are being absorbed by the material and not transmitted back to the eye. For instance, a yellow appearance is an indication that colors in the blues and green range are being absorbed. Therefore, a colorless diamond will return virtually all of the light energy it sees, absorbing only a negligible amount making them whiter and brighter than diamonds with more body color.

A diamond is a tiny sculpture made of mirrors designed to create a beautiful display of lighting effects - brilliance, fire, and scintillation. This light performance is like a symphony playing a variety of instruments all designed to bring out the best in the score. To the extent that the diamond cutter has crafted a masterpiece, diamond will display an optimal balance and range of the most beautiful light effects that are finely tuned masterpiece for the eyes.