Lighting and Diamonds

Light helps to draw out the aesthetics of a diamond. A well-made cut showcases the beauty of the jewel by encouraging light to illuminate the diamond, split into many hues, and sparkle for the pleasure of the viewer. Not all forms of lighting are equal. Different types have varying concentrations that underscore specific diamond traits.

To shine a spotlight, or a direct beam of light on a diamond draws out its fire. This is accomplished by suppressing a diamond’s brilliance, or the amount of white light in the stone. The jewel darkens, drawing attentions to flashes of colored light, or fire, within the gem. Incandescent lighting such as from light bulbs further help to underscore fire.

With diffuse or scattered lighting, brilliance is emphasized. Light enters the diamond from multiple directions, downplaying shadows. Brilliance comes to the forefront while fire is diminished. Diamonds under fluorescent lights showcase the jewels’ white light.

To help connoisseurs select diamonds, jewelers often display their gemstones under a blend of fluorescent and incandescent. Spotlights may be used in displays to help play up the jewel’s fire, making sure it’s not overshadowed by brilliance. Some vendors may use colored lights or backgrounds to further play up the contrast between brilliance and fire.


Top-Down Shadows
Diamond cuts are designed to make the jewel appear pleasing when viewed from the table, its flat uppermost facet. With brilliant cut diamonds, this means showcasing brilliance, fire, scintillation and other displays of light. For step cut diamonds, the jewel’s luster and clarity come to the forefront. Other visual effects are possible.

Renaissance table cut diamonds sometimes followed contemporary interest in geometry and proportion. While some variations were plain, others had an additional facet on the bottom of the stone. When viewed from the table down, the diamond appeared to have a square within a square.

Modern diamonds too are subject to interesting top down features. Sometimes the crown, or upper portion of a brilliant cut diamond is laser-polished into a dome shape rather than faceted. The resulting gems are known as buff top diamonds. When viewed from above, their lower facets may resemble stars.

Some effects are not as desired. With brilliant diamonds, cutters strive for a balance between brilliance, fire and scintillation. Stones with light leaking through their sides can end up with more shadow than brilliance. More facets may be visible than intended, or overly large dark spots may appear beneath the table.

A common quirk in fancy cut diamonds such as marquise or pear cuts is a shadow in the center resembling two connected triangles. Known as a bow tie, it’s a result of the cuts’ symmetry. While stones such as round brilliants have multiple lines of symmetry which promotes even light distribution, many fancy cut diamonds may have as few as one line, leading to dark spots. Diamond cutters try to shape these cuts to minimize the bow tie effect.


Diamonds and the Speed of Light
At their most basic, diamonds are made of clusters of five carbon atoms. Each group is bonded together through shared electrons, which keep the atoms close together. This composition leads to crystals of remarkable hardness as well as optical effects.
Light is extremely fast in a vacuum, but changes speed as it travels through another object. The denser the material, the slower light becomes. With air, light moves at about 300,000 kilometers a second, while it travels at 225,000 km through water. Diamonds’ tight knit atoms forces light to move at a leisurely 124,000 km per second.

Diamonds can cause other quirks to occur with light. When light hits a diamond perpendicularly, it simply slows down. If it hits a diamond at any other angle, it changes direction, a trait known as refraction. Due to the density of its composition, light bends drastically within the jewel, giving diamonds a high refractive index.

For centuries, diamond cutters have taken advantage of the stone’s refractive index to add light to the jewel. By playing with facet arrangements, depth, symmetry and other factors, jewelers made diamond cuts with greater amounts of brilliance. The search to make the brightest diamond possible continues to this day.


Diamonds, Northern Light and Grading
Light is essential for drawing out the best in a diamond. There are many ways to describe how light interacts with the jewel, including brilliance, fire, scintillation and luster. A skillfully cut brilliant diamond will showcase all of these traits. At the same time, light isn’t uniform. Various types underscore different aspects of the gemstone.

When it comes to grading diamonds, consistency is key. Changes in environment may influence the appearance of the gemstone, impacting the accuracy of the evaluation. Additional complications include the way certain types of lighting may accentuate some diamond qualities while suppressing others, such as how fluorescent light emphasizes fire at the expense of brilliance.

Before advances in artificial lighting, north facing daylight was popular for evaluating diamonds. One of its major advantages is its neutrality. It’s less likely to accidentally give color to a diamond that the jewel doesn’t have. In a pinch, those who need to study gemstones away from the lab may still use north facing light at a consistent time and location.

Modern grading boxes are designed to emulate this light, to better grade diamonds for accurate color. They also have multiple lighting types that gemologists can switch between in order to determine different aspects of the stone. There are spotlights to grade fire and diffused lighting to examine brilliance. Accurate grading is essential, and appropriate lighting helps with this goal.