What is Diamond Fluorescence and is it Good or Bad? 

Have you ever heard the term ‘fluorescence’ when jewellery shopping and wondered what it actually means? In this guide, we’ll share the definition of the term, how fluorescence affects the diamond's appearance as well as its value and price, and what to keep in mind when you start diamond shopping and whether this will be a big factor in your final decision.  

 

What is fluorescence and why do diamonds have it? 

Diamond fluorescence refers to a phenomenon where a natural diamond emits a visible glow when exposed to ultraviolet (UV) light as a result of its formation. The composition of a diamond is established deeper than 100 miles below the Earth’s surface from a mixture of extreme heat and pressure which can trap minerals within the stone during formation. When other elements, like nitrogen, aluminium and boron, are trapped inside layers of carbon during the diamond formation, they can absorb UV light and produce both colour and fluorescence. This is later re-emitted as visible light, but only under a UV source. 

 In the same way that inclusions or crystal structures are natural characteristics for diamonds, fluorescence is naturally occurring and appears varied and unique across diamonds even when they have been mined closely together. Fluorescence has also been present in diamonds for millions of years, so this isn’t a new occurrence, and shares no correlation with issues around quality or damage. 

 

Can lab-grown diamonds have fluorescence? 

Yes, some lab-grown diamonds can also have fluorescence despite being man-made. The glowing effect may be added during colour-changing irradiation and heat treatment in labs. Essentially, radiation and temperature changes in lab-grown environments are usually for diamond treatment to create different beautiful colours. This treatment is replicating a similar environment to natural diamond formation where exposure to different minerals can affect the chemical composition of the diamond including its fluorescence. Understanding what fluorescence is helps explain another difference in how a diamond is graded and valued. The next step is to understand the different grades of fluorescence in a diamond and how that affects the diamond’s value. 

 

Does every diamond have fluorescence? 

No, not all diamonds have fluorescence. A large proportion of diamonds have no detectable fluorescence and are graded as ‘None’. According to GIA (Gemological Institute of America) data, roughly 25% to 35% of diamonds exhibit some degree of fluorescence when examined under UV light.  

 

How is diamond fluorescence measured? 

 

 

Diamond fluorescence is measured by trained gemmologists at diamond grading laboratories using a standardised long-wave UV lamp in a controlled, dark environment. The UK follows the GIA grading system, which rates fluorescence on a five-point scale: 

• None 

• Faint 

• Medium 

• Strong 

• Very Strong 

 

These grades range from no detectable glow to an intense glowing effect. The colour is also noted during grading, with it typically being blue in 95% of cases, but sometimes yellow, white, green, or other colours.  

The natural human eye can’t reliably distinguish between subtle differences in fluorescence intensity under normal lighting conditions, like under your ceiling lights, morning daylight or in a beautifully lit jewellery store. This is why fluorescence is only detectable under specialised UV lighting, not in everyday viewing conditions. 

 

Does fluorescence impact the price of a diamond? 

Yes, fluorescence may influence the price of a diamond, but maybe not in the way you might expect. The pricing largely depends on the diamond’s colour grade and the strength of fluorescence. As fluorescence isn’t one of the main grading factors like the 4Cs – cut, clarity, carat and colour – it’s simply a characteristic of the diamond which can impact the value of the diamond after the main factors, meaning every diamond’s price can be influenced by the fluorescence grade and the price can be a minimal difference or a big difference depending on the grading.

 

Higher colour grades 

The impact of fluorescence on the final price varies dramatically by the diamond's colour grade. In colourless diamonds (D-F), fluorescence typically will not affect the  value. These diamonds may have discounts associated with their value because fluorescence makes them seem less pure – but again, this is subjective. The true value of every diamond is intrinsic and entirely up to the buyer or wearer. 

 

Mid-range colour grades 

Diamonds in the G-H colour range with blue fluorescence typically receive moderate price discounts, though less severe than higher colour grades. This is because these near-colourless diamonds will not benefit significantly from fluorescence grading, but the market perception influences their value. Research from GIA shows that fluorescence has virtually no impact on a diamond’s appearance without U.V light. However there are the rare exceptions reported where diamond graders stated they could notice diamonds with fluorescence present to have an existing haze within the tone, however majority of graders disagreed with this theory and it was not approved by GIA grading.

 

Lower colour grades 

A large majority of I-M colour graded diamonds often have a faint yellow hue, so some professional gemmologists and jewellers believe the levels of blue fluorescence can enhance the diamond colour in natural daylight by making them appear whiter and therefore increasing their value. Essentially, the chemical imperfections which create the glow counteract its natural yellow colour, this is why you may see diamonds in these colour grades with fluorescence that have a greater value that diamonds graded with ‘none’ and can be surprising to a customer without being aware of the impact it has on the stones colour.

While the prices for diamonds with levels of fluorescence may be dynamic, it shouldn’t be the only deciding factor when you’re comparing these remarkable diamonds. Your decision should be based on the diamond’s four c’s dimensions and overall allure, your personal preferences and your budget, rather than fluorescence alone. 

 

So, is fluorescence good or bad in a diamond? 

When considering if fluorescence is good or bad in a diamond, it depends on your goal when purchasing a diamond. Even some professional jewellers and gemmologists have varying opinions on fluorescence. There’s no universal right answer. Some buyers may prefer faint to medium fluorescence in lower colour grades, as it makes diamonds appear whiter in lower colour grades where faint yellowing is present, which can make a lower graded diamond appear to be a higher quality for a reasonable price. If you’re purchasing a high colour grade for value retention, you might prefer a non-fluorescent diamond for a better chance of holding the diamonds value whether that is to pass down the family generations or for its potential resale in the future. And if you’re buying an engagement ring, personal preference is what matters most. 

 Overall, the most important factor is how the diamond looks to you in person under various everyday lighting conditions.  

 

How to identify diamond fluorescence when visiting a jeweller 

It’s difficult for the human eye to identify the level of fluorescence in a diamond. When inspecting a diamond for your loved one’s engagement ring or a thoughtful gift for a cherished family member, you should observe it under various, realistic lighting conditions, such as:
 

• Natural daylight (near a window) 

• Indoor lighting (overhead lights or spotlights) 

• U.V Fluorescent lighting (most jewellers should provide this)

• LED lighting 

You could compare diamonds of the same colour grade side by side to spot any subtle differences. Our Shining Diamond experts are always on hand to offer any guidance and provide the tools you need to compare different diamonds on the day of your visit.  

 

What’s the next step in your journey to finding your perfect diamond? 

The best way to find a diamond you will treasure forever is to visit us and experience holding a loose diamond in your hand and analysing it in person with our guidance to help you choose the perfect diamond for you. Book an appointment at our Birmingham, Brighton or London stores to explore our carefully curated collection of diamonds with expert guidance tailored to your preferences and budget.