Food

The Science That Makes Some Food Glow Under A Blacklight

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If you're a night owl, you may have found yourself in a club or at a party some weekend, illuminated by the unearthly haze of a blacklight. You may have also found that the light made your gin and tonic glow a bright blue. That's no accident—that's just old fashioned fluorescence.

Related: Every Human Is Bioluminescent

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What Makes Things Glow?

No matter what it is that's glowing—tonic water, a white T-shirt, your own teeth—it all comes down to the interaction between UV light and substances called phosphors. A phosphor, by definition, is any chemical substance that can be energized by one type of light to emit visible light. If they only emit light while they're being energized, they're called fluorescent. The quinine in your cocktail's tonic water contains phosphors, for example. A blacklight emits most of its light in the ultraviolet (UV) part of the light spectrum, which is just beyond the range the human eye can see. Even though it's invisible to us, those UV light waves hit the phosphors in the tonic water and excite their electrons, making them stray farther from the atomic nucleus than normal. When they return, some energy is lost, so the light wave that returns to your eyes has a slightly shorter wavelength—one that you can see. Voila, the tonic water appears to glow.

Related: Scorpions Glow Under UV Light

Fresh, Tasty, And Glowing

Tonic water isn't the only edible thing that's fluorescent. Chlorophyll in plants is too, though it takes some doing to see it. You can see it breaking down in ripening bananas, which glow blue under UV light, or in pulverized greens like spinach and cilantro, which glow red.

Related: These Glasses Make Tumors Glow So Surgeons Can See Them

Another group of fluorescent chemicals are known as flavins, and appear in things like honey and liquid vitamin B12—a.k.a. riboflavin. Have a blacklight at home? Clear out your pantry and try it yourself—there are plenty of fluorescent foods and beverages to discover.

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Watch And Learn: Our Favorite Videos About Fluorescence

How Do Blacklights Make Things Glow?

It all comes down to phosphors.

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Key Facts In This Video

  1. Blacklights mostly emit only higher-frequency ultraviolet light, which is outside the visible light spectrum. 00:37

  2. Phosphors are substances that absorb electromagnetic energy coming from a light source then emit the light they've absorbed at a lower, visible frequency. 00:58

  3. Human teeth, fingernails, and certain bodily fluids contain natural phosphors, which is why forensic investigators use blacklights at crime scenes. 01:35

How Does Fluorescence Work?

Here's the science behind that glow.

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Fluorescent Hacks

Some of this you definitely shouldn't try at home.

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