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Do Diamonds Glow Under Black Light (UV Light)?

Do Diamonds Glow Under Black Light (UV Light)?

We all know that diamonds shine magnificently when viewed under daylight. That gorgeous sparkle is something that everyone admires. 

But how do diamonds act when exposed to the blacklight? Do diamonds glow under black light?

The answer is – YES. Diamonds do glow under the blacklight – or at least a certain amount of diamonds does. That is due to their characteristic called fluorescence. 

You may be asking what fluorescence is? And while we’re at it, is this fluorescence a bad thing for a diamond? Answer to these – and many more – questions can be found in this article, so be sure to read it until the end.

What Is Black Light?

Black light is UV (ultraviolet) light or lamp that emits almost all of its light in the ultraviolet segment of the spectrum. Human vision can’t detect black light, so a room illuminated with black light still appears dark. 

A device that emits black light is called black light or Wood’s lamp. The name “Wood’s lamp” honors the inventor of glass UV filters, Robert Williams.

There are several types of black light, including LEDs, incandescent lamps, special fluorescent lamps, and lasers. All of these produce a unique spectrum of light.

Black lights can also be used to observe fluorescence – for example, in diamonds – to attract insects, in tanning beds, for artistic effects, to cure plastics, and for disinfection.

Why Is Black Light Called Black Light?

The name “black light” comes from ultraviolet (UV) light being invisible to humans. If blacklight lamps only emitted ultraviolet light, it wouldn’t be possible to see it.  

Most black lights look violet or blue because they emit short-wavelength visible light. That is what makes it possible to tell if the light is on or not.

However, some UV lamps and lasers emit only invisible radiation.

Types Of Black Light

As we mentioned earlier, the so-called black light comes in many different forms. There are fluorescent lamps, incandescent lights, LEDs, lasers, and mercury-vapor lamps. 

Incandescent lights emit very little UV light, so they make poor black light sources. An incandescent black light has a filter that permits the passage of UV wavelength and blocks visible light.

Fluorescent black lights cost a bit more than previously mentioned lights – but they’re more energy-efficient, more bright, and don’t overheat. Bug zappers use these types of bulbs, for example.

UV lasers emit coherent, monochromatic radiation that is invisible to the human eye. It’s crucial to wear eye protection when operating with such devices, as the light can cause immediate and permanent blindness.

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Black Light Uses

Black lights have many uses. UV lights are used to improve the brightness of phosphorescent materials, observe fluorescent dyes, promote melanin production in the skin, illuminate artwork, and cure plastics. 

There are several medical applications of UV light, as well. UV light is used for diagnosing fungal infections, bacterial infections, and melanoma, and it can be used in disinfection and treating neonatal jaundice.

Black Light Safety

Most black lights are pretty safe because the UV light they produce is in the longwave UVA range. That is the region closest to one of visible light. UVA has been associated with skin cancer – that’s why you should avoid extended exposure to black light radiation.

UVA penetrates deep into the skin, where it can damage DNA. And while UVA doesn’t cause sunburn, it can destroy vitamin A, damage collagen, suppress immune function, and promote skin aging.

Some black lights produce more light in the UVB and UVC ranges. These lights can lead to burned skin. Because these lights have higher energy than UVA, they can damage cells more rapidly.

UV lamps and lasers are very powerful. They emit oxidizing radiation that burns human tissue and kills microbes.

What Is Diamond Fluorescence?

Now, back to diamonds. Fluorescence in diamonds is the glow you can see from certain diamonds when they’re under UV light. Around 30% of diamonds glow to some extent under UV light. 

When exposed to black light, these diamonds can produce fluorescence in different colors. The glow is blue 99% of the time – but on some occasions, diamonds can glow white, green, yellow, and even red.

The GIA grades fluorescence in diamonds in different grades:

  • None
  • Faint
  • Medium
  • Strong
  • Very strong

So if you’ve asked yourself what fluorescence is, think about how UV light makes your white clothes appear whiter. In the same way, some gems will show fluorescence under UV light. 

Fluorescence can improve the diamond’s color – but it could also make it appear hazier. 

How Does Diamond Fluorescence Impact The Price And Appearance?

You should note that some diamond color grades pair better with specific diamond fluorescence grades from a visual standpoint.

For example, the highest color grades tend to have higher prices if they’re paired with none fluorescence than with faint fluorescence.

Meanwhile, lower color grades tend to price rather consistently across none, faint, and medium fluorescence.

Let’s take two diamonds that are both 1-carat, and both have D color grade and VS1 clarity grade. One that has none fluorescence grade will cost $8546, and the other has a very strong fluorescence grade and will cost $6433.

Purchasing a diamond with none fluorescence costs about 33% more than the very strong fluorescence diamond – even if they look almost identical.

That is because fluorescence can help offset some of the colorations in a diamond. 

However, when there’s no coloration in a diamond, any fluorescence is usually viewed as unnecessary – and even undesirable.

Very strong fluorescence may even make a diamond look hazy, and for this reason, it tends to be less favored than the other grades of gem’s fluorescence.

Remember: The higher color grades will be priced remarkably higher for none or faint fluorescence than medium or strong fluorescence. For the lower color grades, the pricing is relatively flat. Many people who want to buy diamonds tend to favor some fluorescence to aid in offsetting the natural color that is present in these lower color grade diamonds. 

None Fluorescence

None fluorescence is the most common fluorescence intensity, with around 67% of diamonds graded as such. 

When the GIA grades a diamond with the grade of none fluorescent, it doesn’t necessarily mean that that diamond isn’t fluorescent at all. Instead, this grade means that the fluorescence is so faint that it’s almost non-existent. 

None of the diamond color grades are affected by the non-fluorescent grade. None fluorescence dictates a higher price than any other fluorescence grade. However, it can command a slightly lower price in lower color grades on a case-by-case basis.

Fluorescence is to blame for this pricing phenomenon as it can help offset the looks of color in a diamond. All diamond colors can be paired with none fluorescent grade, but it works best with colorless diamonds.

Faint Fluorescence 

About 18% of diamonds graded by the GIA have a faint fluorescence grade, making it the second most common fluorescence grade. 

As the name implies, faint fluorescence means the diamonds show a minimal amount of fluorescence when exposed to the blacklight. Also, the fluorescence intensity is insignificant, so it doesn’t seriously affect the diamond’s looks. 

However, faint fluorescence is usually recommended for people who want to buy lower color graded diamonds. It can slightly help to offset some of the color saturation connected with those diamonds.

You can pair faint fluorescence with all diamond color grades, but we especially recommend for G or lower color grades as it can offset minor color saturation.  

Medium Fluorescence

Medium fluorescence is usually the level at which buyers become a bit nervous that the diamond’s looks will be negatively affected by the intensity of the diamond’s fluorescence. It especially becomes an issue in colorless diamonds. 

However, diamonds with this grade can offer great value in certain situations and even positively affect lower color grades like J or K color, which may show some color saturation. 

While the influence is usually minimal – and only noticeable under the blacklight – medium fluorescence aids in offsetting the often yellow color of a diamond by adding a blue hue to the gemstone in UV light or natural light. 

That can make the diamond appear whiter and can give the diamond more life. The recommended color grade for pairing with medium fluorescence is G or lower colored graded diamonds.

Strong Fluorescence

In certain situations, diamond fluorescence can actually negatively affect a diamond by making it appear hazy or oily when exposed to blacklight.

Because of this, it’s highly recommended that you observe the diamond in natural light and determine if the diamond shows these negative effects. For color grade K and lower, strong fluorescence typically helps offset the color saturation within the diamond. 

However, strong fluorescence should often be avoided in the higher color grades because it’s more likely to impact these diamonds in a negative way. We recommend J or lower color graded diamonds for pairing with strong fluorescence.

Very Strong Fluorescence

This fluorescence grade is extremely rare and is more likely to negatively affect a diamond’s visual aspect by making it look more hazy or oily. For this reason, we wouldn’t recommend you seeking out diamonds with strong fluorescence.

Negligible Fluorescence

One notable fluorescence grade is negligible fluorescence, and it’s a grade specific for the American Gem Society that doesn’t differentiate between none and faint fluorescent grades. 

It’s the grade that is given to diamonds that show a minimal level of fluorescence. It shouldn’t affect the appearance of the diamond in any color grade. 

As such, it can be recommended for pairing with all diamond colors.

Is Diamond Fluorescence Good Or Bad?

Diamond fluorescence isn’t necessarily bad nor good. 

As we mentioned above, there are some situations where diamond fluorescence can help offset some of the colors, especially in lower color grade diamonds. It can also make those diamonds look whiter.

In addition, a small amount of fluorescence can make a diamond appear more lively thus more sparkly. On the other hand, too strong of fluorescence can make a diamond look hazy and oily.

Can Sunlight Affect Diamond’s Fluorescence?

Sunlight is actually 10% UV light, which means that diamonds with some fluorescent properties will exhibit fluorescence slightly when exposed to daylight. It’s also important to take note that diamond will reflect its environment.

For example, a diamond with an H color grade observed in the sunlight can appear blue. But this doesn’t mean it’s exhibiting its fluorescence and is instead reflecting the clear blue sky. 

See Also: How Should A Diamond Look In Sunlight?

Will Diamond Glow At The Night Club Or Bowling Alley?

If the diamond has fluorescent properties of any level, there’s a chance that it will glow under UV lighting. The stronger the fluorescence intensity, the higher the chances your diamond will exhibit fluorescence and glow when exposed to UV light. 

And yes, that includes clubs, too. 

What Different Colors Of Diamond Fluorescence Exist?

Diamond fluorescence can come in many different colors – but the most common one is the blue color. Some diamonds are listed as strong blue fluorescence – this means that they have a strong fluorescence grade of the blue variety.

Other diamonds can exhibit colors like green, yellow, white, and purple when exposed to the blacklight.


Chances are you’ve noticed that your white shirt appears to be whiter and to glow when you enter a nightclub with UV lighting. 

But if you asked yourself, “Do diamonds glow under black light?” we’re here to explain it to you:

Black light is UV light that emits all of its light in the ultraviolet spectrum. It can’t be seen by the human eye, but certain materials will glow under this light.

Diamonds are one of those materials that glow under the blacklight – or at least some of them do. That is due to their fluorescent properties. 

Diamond fluorescence is graded in several intensities – none fluorescent, faint, medium, strong, and very strong. Diamond fluorescence can sometimes be good as it can help alter some of the discolorations in the diamond.

On the other hand, very strong diamond fluorescence can make a diamond appear oily and hazy, so you should avoid this grade of diamond fluorescence.

Learn More: Why Do Diamonds Turn Blue In Blacklight?