Why Does Your Diamond Glow Under UV Light?

When you hear the phrase “diamonds are forever,” you probably think of a sparkling gem reflecting light off its many facets. But did you know it can produce an amazing display of lights when exposed to ultraviolet radiation? So why does your diamond glow under UV light?

Diamonds glow under UV light because of the interaction between the trace elements present in their crystal lattice structure and the surrounding environment. This glow is also known as fluorescence, and different diamonds have differing fluorescence levels.  

In this article, we’ll investigate the reasons for the glowing of diamonds under UltraViolet (UV) light, how this affects their value and some intriguing facts about diamond fluorescence.

Diamond Fluorescence Explained

Some diamonds emit an eerie glow when exposed to sunlight or black light. This effect can be attributed to two main factors: the type and amount of impurities within each diamond. 

The Science of Fluorescence 

Fluorescence is an intriguing phenomenon that has fascinated scientists for centuries. This remarkable process occurs when a material absorbs short-wavelength radiation, such as ultraviolet light, and re-emits it at a longer wavelength in the visible spectrum.

When electrons within an atom are exposed to high-energy photons such as those in ultraviolet rays, they jump into higher orbital shells – resulting in fluorescence emission. 

The closer the jump of an electron, the more energy is required to excite it. UV light is thus required to catch such visible fluorescence. 

While this may seem strange, there are several scientific explanations for why it happens in diamonds. Chief among these is the presence of impurities, particularly those caused by nitrogen. The color and brightness of the fluorescence vary depending on the number of nitrogen atoms.

The Five Levels of Diamond Fluorescence

The intensity of a diamond’s fluorescence depends on the number of trace elements like nitrogen, boron, and aluminum present in its pure carbon crystal structure. There are five levels of diamond fluorescence developed by the GIA.

  • Very Strong Fluorescence – typically emits intense blue color and appears cloudy. These types of diamonds should be avoided.
  • Strong fluorescence – emits a neon blue glow. This glow benefits lower-graded diamonds because it tends to mask color imperfections.
  • Medium fluorescence – usually presents a greenish or soft blue emission and can effectively reduce the price.
  • Faint fluorescence – generally has a yellowish hue with just enough brightness to be noticed by the eye. 
  • None/Negligible Fluorescence – No glow is observed under UV light. These diamonds are most desired and thus come with the highest price tags.

Regardless of fluorescence, all diamonds are naturally UV reactive, not just those with a visible glow. According to a 1997 GIA study, only 25-35% of diamonds show fluorescence under UV light.

Advantages of Diamond Fluorescence 

You may get several benefits if you’re planning to buy or already have a diamond that fluoresces under UV light.

  • Diamonds that exhibit fluorescence may have lower prices. So people looking for an affordable option when purchasing jewelry won’t have to sacrifice quality. They can simply opt for a less expensive stone with fluorescence. 
  • It can increase the value of some diamonds. The fluorescence lends a distinctive look to the diamonds under specific lighting conditions. Strong or medium fluorescence levels can improve the color in lower-grade diamonds (J-L).
  • None or negligible fluorescence in a diamond can determine its quality. For instance, D-F grades are considered high-grade diamonds. According to experts, they no longer remain high-quality if they contain strong fluorescence levels.
  • It acts as a form of protection for diamonds exposed to UV light.  Such diamonds include those used in jewelry or even those on display in museums. By absorbing the UV rays, fluorescence prevents any damage from occurring and helps keep the stone looking its best. 

Note: You should always check the diamond grading at your local jewelry shop or free in-store previews of some popular diamond companies. The fluorescence grade of a diamond is found in the AGC (Additional Grading Criteria) section of the GIA report.

Are Diamonds With Fluorescence Cheaper? 

The fluorescent effect is caused by trace elements in the diamond’s structure. While this does not affect its clarity or quality, it does influence the price tag

Diamonds with strong fluorescence are worth much more than others (typically in lower-grade diamonds like J, K, and L). However, Customers often prefer colorless diamonds over those with fluorescence, so retailers have to offer discounts of up to 10-20% to attract buyers. 

Ultimately, several factors affect the price of diamonds, so it is worth checking with your jeweler before making a purchase.

Is Diamond Fluorescence Good or Bad? 

When it comes to diamonds, fluorescence is a topic of much debate. Some people don’t like the appearance of a fluorescent diamond. Others argue that diamonds with fluorescence appear more brilliant in certain light settings. 

Diamond fluorescence is not good or bad, as it is not an indicator of the quality or clarity of the stone. Some jewelers may categorize non-fluorescent diamonds as ideal and charge higher prices for such diamonds, but that is a matter of preference. 

Do Lab Made Diamonds Have Fluorescence? 

Lab-created diamonds, also known as man-made or synthetic diamonds, are created in a laboratory instead of forming naturally on the earth. While these diamonds are nearly identical to mined diamonds in many ways, one aspect of their difference is the level of fluorescence. 

Fluorescent properties vary among lab-made stones depending on how they were created and the type of element used during production. 

For example, CVD (chemical vapor deposition) grown diamond typically has almost none to faint yellowish or brownish fluorescent properties. In contrast, HPHT (high pressure, high temperature) grown diamond will show some degree of visible blue color emission when exposed to UV rays. 


Diamonds are made up of carbon atoms, which contain electrons that can absorb energy from UV light. When the absorbed energy is released, it emits a soft blue-violet glow. This outcome is known as ‘fluorescence.’ The level varies when the diamond contains trace elements like boron, nitrogen, or aluminum. 

Fluorescence in diamonds is neither good nor bad but may affect the price of the diamonds depending on other factors, such as the stone’s quality. 

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