Diamond Fluorescence: Everything You Need to Know

You thought you knew everything important about diamonds, including the “Four Cs”:

  • Cut
  • Color
  • Clarity
  • Carat

Then you find out there’s another quality of diamonds you need to be aware of. It’s related to color. It’s called fluorescence – and it affects around 30% of diamonds.

By the time you finish this guide to diamond fluorescence, you’ll be able to answer the following commonly-asked questions from people new to buying diamonds:

  • What is diamond fluorescence?
  • But what exactly is fluorescence? What causes it?
  • Is diamond fluorescence good or bad?
  • Can you see diamond fluorescence with the naked eye?
  • When does fluorescence improve a diamond, and when does it decrease its quality?
  • What if a diamond glows under a UV light?
  • What if a diamond does not glow under a UV light?
  • Should I buy (or not buy?) a diamond with fluorescence?

What is Diamond Fluorescence?

I’ll tell you what causes fluorescence next. But first, what is it as an experience? Diamond fluorescence is experienced by the human eye as a soft glow emitted from a diamond when it is exposed to sunlight or to a UV or “black” light.

The glow can vary some in color from blue to a dull orange. It’s most visible of course in a darkened room when a diamond is exposed to a UV light.

Around 30% of naturally occurring diamonds are fluorescent.

What Causes Diamond Fluorescence?

Fluorescence is caused when the electrons in certain diamonds (and certain samples of other crystallized stones) absorb UV energy, and begin to release that energy immediately.

It’s similar to phosphorescence in that way. You’re probably familiar with glow-in-the-dark child’s toys. You’d put them in the sun when you were a child. Then you’d carry them to a dark room and watch them glow.

In phosphorescence, the absorbed UV energy is absorbed, then released slowly.

In fluorescence, the energy is absorbed and then released immediately, in a continuous flow of energy in and out.

In both processes, UV light is absorbed, then released. So if you have the pleasure of seeing a diamond fluoresce in a dark room, using a UV light, that’s what’s happening. Electrons in the crystallized gemstone are absorbing energy from that light and then re-emitting it immediately, in a blue color, or an orange color. (Blue is much more common.)

Whatever color a diamond fluoresces, that’s the color it always fluoresces. It won’t change from blue to orange, or from orange to blue.

Is Diamond Fluorescence Good or Bad?

Ultimately, that’s a completely subjective opinion. But there is general agreement, in this subjective opinion, which affects the price of diamonds. It’s this:

  • Diamonds of colors I through M can benefit somewhat from blue fluorescence.
  • Diamonds of colors D through F suffer somewhat from blue fluorescence.
  • Any gemstone diamond suffers somewhat from orange fluorescence, which is rarer than blue fluorescence.

A Quick Review of the Diamond Color Scale

Remember, there are no colors A through C in the GIA diamond color scale.

Before the GIA (Gemological Institute of America) created an objective, measurable color scale in 1953, “grades” of diamond color varied widely. They were called A, or B, or C, or AA, or AAA, without any reference to a standard, scientific, measurable color scale.

The GIA wanted to start fresh, with no confusing references to “A” or “B” or “C”. So they started with “D.” That’s why “D” is the absolute best, most desirable diamond color grade. A, B, and C do not exist on the scale.

As you go to E, F, G, and all the way toward Z in the GIA color scale, the colors of diamonds get more and more yellow.

Diamonds beyond the color M are rarely if ever used in jewelry, and certainly not in fine diamond engagement rings.

Why Do Diamonds of Colors I Through M Benefit Somewhat From Blue Fluorescence?

It’s because fluorescence is generally blue, and the diamond colors I through M are progressively more yellowish.

In sunlight, a diamond with a blue fluorescence emits some blue. Because blue cancels out yellow, the diamonds with a yellowish tinge (colors I through M) appear more white and clear in sunlight, if they have blue fluorescence.

You might be thinking, “Don’t these slightly yellowish diamonds appear to be green if they fluoresce blue?”

Good question. If you mix blue and yellow solid colors, you do of course get green.

But when you mix blue and yellow light, you get white. Diamond color is defined by the light passing through the diamond.

Why Do Diamonds of Colors D Through F Suffer in Quality From Any Fluorescence?

It’s because diamonds of colors D through F are very clear and white. If a diamond is of color D (perfectly white), and it fluoresces blue in sunlight, then that diamond will have an unfortunate blue tinge in sunlight.

What About the More Rare Orange Fluorescence?

(Orange fluorescence in a diamond is not fully orange, but it’s a kind of yellowish, orangish fluorescence.)

Diamonds of color I through Msuffer in quality from an orangish fluorescence. You can see why. These diamonds are progressively more yellowish in color, the closer you get to M, which is the most yellow of any diamond typically used for jewelry.

So, if you mixed orangish fluorescence with yellowish light from the diamond itself (color grades of I through M), you get an even more orangish, off color diamond.

And of course, diamonds of colors D through F (very white diamonds) are going to suffer from any orange fluorescence as well. They’ll be tinged orange.

That’s why orange fluorescence in any diamond is bad. Unlike blue, which can cancel out some yellow in sunlight, orange fluorescence just makes everything worse. And never makes anything better.

Is Strong Fluorescence in a Diamond Bad?

In general, strong fluorescence in a diamond is not desirable. It can make a diamond look as if it has an oily sheen, in sunlight. Or else it can give it a faint, but unmistakable amber tinge.

What About Strong Blue Fluorescence?

It’s not fantastically good, and you can see why, based on what you’ve learned so far:

  • Strong blue fluorescence might overpower even a slightly yellow diamond.
  • And it can give the diamond the appearance of an oily sheen, as if it’s slightly dirty with grease.

Can You See Diamond Fluorescence?

It depends on the strength of the fluorescence. In general, to the naked, untrained eye. It’s not something you’d notice. But if you’re looking for it, and you have relevant experience with diamonds, you can spot a strong fluorescence in sunlight.

You can see it especially if you look for it with a UV light in a room that isn’t very bright. If the diamond you’re examining is one of the nearly 30% of diamonds which exhibit fluorescence in UV or sunlight, then you’ll most often see it glow a kind of purple, or blue — or else a dull orange.

Do Fake Diamonds Glow Under UV Light?

They absolutely can. It depends on what was used to make the fake diamond. If a little kid’s yoyo can glow in the dark, or your T-shirt glows under the UV lights at the club, then anything can be manufactured to glow under a UV light.

The bottom line is that some diamonds glow under UV light, and some don’t.

Getting out your UV light to test the authenticity of a diamond would be a total fail. It’s not at all a test to know if a diamond is real.

You Can Select Diamonds for Fluorescence at Reputable Online Jewelers

An even more fundamental bottom line is: If you’re at all worried that a diamond you’re considering could be fake? Then you’re at the wrong jeweler. Just no. Just get out.

Pawn shop? No way. Even if it’s genuine (it could very well be fake), you don’t want that pawn shop tied to the most important relationship in your life forever.

Only buy diamonds from a reputable jeweler.

The only way for a non-professional to know for sure  whether a diamond is fake or real, is to consult a professional.

That’s why we recommend buying your diamond engagement ring only from established, well-known, highly reputable jewelers such as James Allen, Blue Nile, or Brian Gavin.

You can even select and filter for diamond fluorescence at major, reputable jewelers such as James Allen.

diamond fluorescence at james allen
Diamond fluorescence option at James Allen


Now you know what you need to know about diamond fluorescence:

  • In diamonds of color grades I through M, blue fluorescence can be desirable, provided it only compensates, not overcompensates for the yellow.
  • Any fluorescence (even blue) in diamonds of colors D through F is generally undesirable. That’s because these are very white diamonds, and that color is highly prized.
  • In diamonds of colors G and H, it could go either way if the fluorescence is blue, and weak. But orange is never desirable.
  • Orange fluorescence (which is rare) isn’t generally desired in any color of diamond.
  • Most people can’t tell much difference, can’t really even spot the fluorescence (blue or orange) unless they’re really looking hard for it, possibly even requiring a shady room and a UV light.