What is Diamond Fluorescence? – Diamonds Under Black Light

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What is diamond fluorescence? Diamonds under blacklight or UV light glows blue or white are fake or real? These are the most common questions people ask us about fluorescent diamonds.

So Today, in this blog post, we will go to learn about diamond fluorescence.

What is Diamond Fluorescence?

what is diamond fluorescence

Diamond fluorescence refers to the effect of UV light on a diamond. When a diamond is exposed to ultraviolet light (also known as blacklight), it glows blue. Sometimes you might see another color too like yellow, green, red & white, but blue is the most common fluorescent color in a diamond.

Let’s make it simple to understanding diamond fluorescence. When you stand under blue light or ultraviolet light in the nightclub, your teeth sometimes glow white looks more bright. Similarly, when a diamond is placed under black light, it glows. However, not all diamonds have fluorescence, some are fluorescent free called “None” in the GIA diamond report. Only 30% to 35% of diamonds have fluorescence.

Labs describe fluorescence by its intensity or strength of the diamond’s reaction when sourced to UV light. Below are the five types of diamond fluorescence you will find on the GIA diamond certificate.

Types of Diamond Fluorescence

  1. None Fluorescence – Diamonds with no fluorescence
  2. Faint Fluorescence – Diamonds with very slight fluorescence
  3. Medium Fluorescence – Diamonds with fluorescence
  4. Strong Fluorescence – Diamond with strong fluorescence
  5. Very Strong Fluorescence -Diamond with intense fluorescence

So, what is medium blue or strong blue fluorescence in the diamond report?

The term “blue” with fluorescence on the report refers to the fluorescence color of that diamond. You might have seen “Strong Blue” or “Medium Blue” stated on a diamond certificate, which means diamonds emit “blue” (fluorescence) light when sourced to UV light.

AGS lab uses the word “Negligible” on a certificate to describe a diamond with no fluorescence.

Diamond Fluorescence Price & Valuation

Fluorescence has a significant impact on diamond value. A diamond with strong fluorescence is 15 -20 % cheaper than of none fluorescent diamond. Below is just to give you a basic idea about the diamond price difference with the change in fluorescence.

Example from Brian Gavin – Both diamonds with AGS lab certificate

Stone 1 – 1.05 G VS2 Ideal – Strong Blue fluorescence – 8148 US$

Stone 2 – 1.02 G VS2 Ideal – Negligible fluorescence – 10261 US$


The above example shows an 18-22% price variation with two similar diamonds with different fluorescence.

How it works – Diamonds Under Black Light

(left) Holding pear shape diamond under black light & (right) diamond under daylight.

To understand why diamond turns blue under black light. We first have to take a look at the science of fluorescence.

What Causes Fluorescence In Diamonds

The Science – Chemical in diamond’s crystalline structure absorbs and re-emits the energy as visible light known as fluorescence.

When elements such as nitrogen, boron, or aluminum are presents in the diamond’s automatic structure. Energy from UV light is absorbed by electrons, which react back to the higher state of energy, termed as “fluorescence” in a diamond.

Diamond Fluorescence – Good or Bad

diamonds under black light

Now, the big question. Is fluorescence in diamond good? Or bad?

Well, It entirely depends on personal preferences. Below points might help to judge how good/bad is fluorescence in a diamond.

  • If you are buying the lower color diamonds like “I-J-K-L color”, consider buying it with faint/medium/strong fluorescence instead of none fluorescence. Why? Fluorescence in diamond creates whiteness (brightness) and reduces yellowness. Therefore, color “J” sometimes looks like a color “I” in daylight.
  • “Very Strong” fluorescence sometimes results in haziness in a diamond. A diamond with “very strong” fluorescence might look oily & hazy in daylight. Still, you can go with “faint” or “medium” fluorescence.
  • A diamond with fluorescence is cheaper.

Buying Fluorescent Diamonds Pros & Cons

Let us take a look at some pros and cons of buying fluorescent diamonds.

Pros of the fluorescent diamond.

  • Low In Price – On average, you may get 15%-18% cheaper diamond if you don’t mind buying a diamond with fluorescent.
  • Improves Color – The best part, fluorescence in a diamond, sometimes enhances its color. It reduces yellowness, therefore, looks better in color to observers.

Cons of the fluorescent diamond.

  • Hazy Diamond – “Very Strong” fluorescence might create a cloudy or hazy look in diamonds. Avoid buying such kind of diamond. It makes the stone look slightly foggy or milky.

Quick Tip – How to tell if diamonds are real or fake?

My Personal views about diamond fluorescence

I like fluorescent diamonds. It is kind of extra cool “glowing in the black light” feature you get with diamond. I always advise consulting experts, gemologists, or gem labs before making any purchase, especially when you set your mind to buy a “very strong/strong” fluorescent diamond.

In extreme circumstances, diamond shows phosphorous. If you figure out your diamond showing afterglow effect, suspect it for further testing of a laboratory-grown diamond.

Never buy blind, physically see the diamond before paying. Ask experts for help; your strong fluorescent diamond might look cloudy.

D-E-F color with very strong fluorescence is less recommended.

In the end, fluorescence is moreover to individual tastes and not good or bad.

Make your decision wisely.

My recommendation for buying a fluorescent diamond online – Once you make up your mind for purchasing a fluorescent diamond, Now the question? Where to buy a fluorescent diamond online?

If you are looking for a diamond with fluorescence, I would recommend you check the James Allen website. They got some great options under the fluorescent diamonds category.

Image Sources & Reference GIA

Harsh Shah

Harsh Shah

Harsh Shah is the director of Pasavaja Gems LLP. He holds various diamond education degrees from GIA, De Beers Institute & Rapaport Acadamy. Harsh love assisting people to buy diamonds with his expert buying skills, market knowledge, and years of experience. Being loose diamond as his family business, he always wants to bring transparency and educate customers about diamonds. Apart from running diamond trading & manufacturing operations, he is extremely passionate about Internet Marketing, SEO & SMM.

17 thoughts on “What is Diamond Fluorescence? – Diamonds Under Black Light”

  1. I have a round 1 karat Solitaire. It is beautiful but glows white under black lights in a club my husband plays in. Should I worry about this? It is appraised as a GHI very good diamond..

  2. I have a blue diamond that show slight flouroscence I believe that flouroscence is green I don’t know if my diamond is colored artificially or natural how can I know?

  3. So, am I reading this correct?
    If the diamond glows with a black light, that is not a good thing or shall I say not as valuable?

    I just recently got a black light to find horn worms on my tomato plants and noticed that my diamond engagement ring glowed.

    Then of course I went and check out all of my other “valuable” jewelry which I know for a fact are real diamonds. Some glowed and some didn’t at all.

    • Based on the intensity/strength of glow under blacklight depends on the valuation. But it’s somewhere between 15-20% less compare to similar diamonds with NO fluorescence.

      Is it bad? No not at all, it depends on personal preferences. Recently, I have sold a diamond with medium fluorescence to a client just because she wants her ring to glow at the party. Isn’t it cool? 🙂

  4. I noticed while getting my nails done today (for the VERY first time) that 2 of my 3 diamonds on my engagement ring glowed blue under the uv nail dryer. Should I be concerned that all 3 are not alike? I have had it for 21 years and it has been into the jewelry shop we bought it from many times over the years. Most recently in Feb 2020.

    • Hi Beth,

      It might be due to fluorescence, it is common. Don’t worry. It’s just valued at 10-20% less to the diamond with no fluorescence. But it’s quite important to buy a diamond with a GIA certificate. It gives you accurate details and confidence about your purchase, hence you don’t end up paying more for the diamond that is less expensive. Hope that was helpful.

  5. My diamond is in an earring and I see more purple than blue Is that a good sigh it’s real and if it fogs at all when I breathe on it it definitely does go right away

  6. Hi,
    I recently bought a chain from a jeweler in New York and was very satisfied with it. For some unknown reason I just happened to want to put it under a black light and some of them glowed. Should I be worried about this.

    • It might be due to the presence of fluorescence in the diamond and should not be the problem unless it makes your diamond looks hazy in daylight (happen due to strong fluorescence). Also, these diamonds are sold 10-25% less than a diamond without fluorescence. Hope that information was helpful. Good Day 🙂

  7. Recently had my nails done under an ultra violet light and I noticed one of the four stones of my engagement ring glowed yellow…should I be concerned?

  8. Everything is a FUCK’N scam,,this world is full of shit,,,can’t even go to a jeweler, big box store and get a real deal,,,,spend 10,000 on. A engagement ring to find out it’s not worth a third of the price,,,,ASSHOLES

    • Hi dear, I feel sorry to hear that. Please let me know if you think we can help you in anyways. I always feel happy and try my best to provide all my knowledge and experiences. Thx

    • Not that I’m for being shady!
      but most sales associates work on Commission.
      It feel its more a hustle or lack of hustle, then a scam.
      When your buying a car, you would take it to a mechanic Pryor to your purchase. or at least know about the item at hand!
      or take a expert with you, any time you make a high $ purchase on anything!



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