The Glow That Divided the Industry

Fluorescence is one of the most misunderstood characteristics of diamonds. It refers to a phenomenon where a diamond emits a soft colored glow when exposed to ultraviolet (UV) light—such as the UV rays in sunlight or black lights. It is a natural characteristic of approximately 25-35% of all diamonds.

What Causes Fluorescence

Diamond fluorescence is caused by the presence of trace elements in the diamond crystal structure. Specifically, nitrogen atoms cluster together in specific configurations within the carbon lattice. When these nitrogen clusters are exposed to UV light, they absorb the UV energy and re-emit it as visible light—most commonly a blue glow, but also yellow, green, white, and (rarely) red. The fluorescence is graded on a five-point scale: None, Faint, Medium, Strong, and Very Strong.

How It Affects Appearance

In Normal Lighting

In normal lighting conditions, fluorescence has no detectable effect on the appearance of a diamond for the vast majority of people. The effect is only visible under UV light. A diamond with Strong fluorescence looks identical to a diamond with no fluorescence under ordinary conditions.

The Exceptions

Two situations where fluorescence can affect appearance:

1. Very strong blue fluorescence in lower-color diamonds (H or below): In some diamonds with a slight yellow body color, very strong blue fluorescence can create an overall whiter appearance because the blue cancels out the yellow. In these cases, fluorescence is actually beneficial.
2. Strong or very strong fluorescence in higher-color diamonds (D-F): In rare cases, very strong fluorescence can cause a diamond to appear slightly hazy or milky in normal lighting.

Under UV Light

Under a UV lamp or strong sunlight, a fluorescent diamond will glow. Whether this is appealing is entirely subjective.

The Grading Scale

• None: No fluorescence detected under UV light.
• Faint: A slight glow barely perceptible under UV light.
• Medium: A visible glow under UV light.
• Strong: An obvious glow under UV light, invisible in normal lighting in most cases.
• Very Strong: A very intense glow. Rarely may cause a slight hazy appearance for higher-color stones.

Fluorescence and Price

Fluorescent diamonds typically trade at a discount of 5-15% for Medium to Strong fluorescence. This discount exists despite the fact that fluorescence rarely affects appearance in normal lighting.

Should You Buy a Fluorescent Diamond?

Buy with confidence if: The diamond has Faint or Medium fluorescence (zero practical impact, price discount is genuine value); you are buying a lower-color diamond (H or below) where blue fluorescence can make the diamond appear whiter; or you find the effect appealing.

Exercise more caution if: The diamond has Very Strong fluorescence and is D-F color (higher likelihood of hazy effect); or you are buying purely online without seeing the diamond.

The Bottom Line

Fluorescence is one of those characteristics that sounds more concerning than it is. For the vast majority of fluorescent diamonds, the effect under normal lighting is invisible. The price discount represents genuine value. A diamond with Strong fluorescence and H color might look better than an equivalent non-fluorescent diamond while being significantly less expensive.

At Aranc

We offer diamonds across the full range of fluorescence grades and are happy to discuss how fluorescence interacts with specific color and clarity combinations.