Diamond Fluorescence: What It Is and When It Matters
By Clint Casmiro, Co-Founder, Smiro Studio · Updated October 22, 2026
Short answer: Fluorescence is a glow some diamonds give off under ultraviolet light, most often blue. Reports grade it None, Faint, Medium, Strong or Very Strong. In most stones it changes nothing you can see in normal light; in rare cases strong fluorescence makes a diamond look slightly hazy. Our IGI reports list it, and we check every stone on video before you choose.
Fluorescence is the line on a report most people skip, and the one that worries people who don't.
What is diamond fluorescence?
A glow under ultraviolet light, caused by trace elements in the crystal, mainly nitrogen. Blue is the most common colour. Sunlight contains UV, so strong fluorescence can show outdoors, not only under a black light. Cutting does not change it.
What do the grades mean?
| Grade | What it means for you |
|---|---|
| None | No glow under UV |
| Faint | A slight glow under UV; not visible in normal light |
| Medium | A clear glow under UV; rarely visible otherwise |
| Strong, Very Strong | A bright glow under UV; occasionally a slight haze in daylight |
The report scale; how a stone looks still needs to be checked on that stone.
Is fluorescence good or bad?
Usually neither. In most diamonds you will not see it at all in everyday light. The rare problem is a strongly fluorescent stone that looks a little milky in sunlight, and that shows up on video. Some people like a blue glow under a black light; it is a personal call.
Faint vs none: does it matter?
Not for how the stone looks. Faint fluorescence is invisible in normal light. Choose between two stones on how they look on video, not on this line.
Where is it on my report?
On IGI reports, beside polish and symmetry, with carat, colour, clarity, cut where it applies and measurements. How to read the rest is in IGI certified lab grown diamonds.
How do we handle it?
We look at the stone, not just the grade. We send you two stones, each with a 360 video and its IGI report, and a hazy stone does not make the shortlist. Our quotes start at F colour and VS1 clarity. More on reports in IGI vs GIA.
Unsure about a fluorescence grade? Send us the report.
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Questions we get about this
What is diamond fluorescence?
A glow some diamonds give off under ultraviolet light, most often blue, caused mainly by trace nitrogen.
Is diamond fluorescence bad?
Usually not. In most stones you cannot see it in normal light; rarely, strong fluorescence makes a stone look slightly hazy.
What is the difference between faint and no fluorescence?
Nothing you can see in normal light. Faint shows only under UV.
What are the fluorescence grades?
None, Faint, Medium, Strong and Very Strong.
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