If you’ve ever noticed your diamond glowing with a blue or other-colored light when placed under a blacklight or ultraviolet (UV) source, you’re not alone. This mysterious glow is caused by a natural phenomenon known as fluorescence, and it can raise questions about the authenticity and quality of your stone. At KRK Jewels, we believe in educating our customers about every aspect of their diamond, including its hidden glow.
Let’s explore what causes this effect, whether it’s a good or bad sign, and what it means for your jewelry.
What Is Diamond Fluorescence?

Diamond fluorescence refers to the visible light that a diamond emits when exposed to UV radiation, such as blacklight. This response is triggered by trace minerals, typically nitrogen or boron, that were present during the diamond’s natural formation process. When UV light hits these elements, the diamond emits a soft glow, most commonly blue, although it may also appear yellow, green, orange, or white in rare cases.
How Common Is Fluorescence in Diamonds?
Fluorescence is relatively common in diamonds. According to gemological studies:
About 25% to 35% of natural diamonds exhibit some degree of fluorescence.
Around 10% show medium to strong fluorescence that is easily visible under blacklight.
While it may seem surprising, fluorescence is a natural optical property, not a defect or flaw.
Different Levels of Fluorescence
Gemological labs like GIA (Gemological Institute of America) categorize diamond fluorescence into five levels:
None
Faint
Medium
Strong
Very Strong
These levels reflect the intensity of the glow when the diamond is viewed under UV light. Most diamonds with fluorescence fall into the “faint” or “medium” category, which usually has little to no visible effect in regular lighting.
Does Fluorescence Affect the Look of the Diamond?

It can — but it depends on the color grade of the diamond and the intensity of fluorescence.
For lower color grades (J to M), blue fluorescence can make the diamond appear whiter and brighter, improving its visual appeal.
For higher color grades (D to F), strong fluorescence may cause a diamond to look slightly hazy or oily in rare lighting conditions.
That said, in most lighting environments, the average person won’t notice a difference in brilliance or transparency due to fluorescence.
Can Lab-Grown Diamonds Glow Under Blacklight?
Yes. Just like natural diamonds, lab-grown diamonds can also exhibit fluorescence. Certain growth processes can even cause unusual fluorescence colors, such as orange or red. This is one of the many ways gemologists can sometimes distinguish between lab-grown and natural diamonds, though fluorescence alone is not a reliable indicator of origin.
Is Fluorescence a Sign That a Diamond Is Fake?
Not at all. Fluorescence is a natural trait found in both real, mined diamonds and lab-grown diamonds. Many authentic diamonds show some level of fluorescence. On the flip side, some fake stones such as cubic zirconia or Moissanite, may also glow under UV, but for different chemical reasons.
If you’re concerned about authenticity, professional grading and certification are the most reliable methods for verification, not just blacklight results.
Should I Avoid Fluorescent Diamonds?
There’s no need to avoid them. Some buyers seek them out, especially if they want a whiter-looking diamond in a lower color range. Others prefer diamonds without fluorescence in high color grades for maximum clarity and brilliance.
At KRK Jewels, we always recommend viewing your diamond in natural, artificial, and UV light before finalizing your selection, so you can be confident in how your diamond looks in all environments.
Summary: What It Means for Your Jewelry
If your diamond glows in blacklight, it’s simply exhibiting fluorescence — a naturally occurring and harmless property. It doesn’t reduce the value or authenticity of your stone and may even enhance its visual appearance in certain cases.
Understanding diamond fluorescence helps you make more informed choices and deepens your appreciation for the complexity of each stone.
Trust KRK Jewels for Expert Guidance
When choosing your ideal diamond, our team at KRK Jewels is here to help you understand all the fine details — from cut and clarity to the subtleties of fluorescence. We offer a curated selection of lab-grown and natural diamonds, each ethically sourced and professionally inspected for brilliance and quality.
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