Why Things Look That Way Under a Blacklight

Why Things Look That Way Under a Blacklight

Have you ever been to a bowling alley or roller rink and noticed that your teeth glow under the blacklight? Or maybe your friend’s teeth glow and yours don’t, sending you running to buy some whitening toothpaste? That cool glowing phenomenon is called fluorescence, and it was discovered and named after a mineral called fluorite.

Fluorescence has far more sophisticated uses than just turning your shoelaces and white T-shirt neon purple. It’s a fundamental property of light that has opened up entire fields of science and engineering. Let’s dive into the crystal that started it all – fluorite – and explore the many ways fluorescence is used today.

What is Fluorescence?

Fluorescence is defined as the emission of light after an object has absorbed light of a different frequency. All light contains energy, and when fluorescent molecules get hit by that energy, their electrons become excited and start to move to a higher energy level, farther away from the nucleus of their atom.

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Everything in nature wants to be at rest whenever possible, so these excited electrons quickly dump their excess energy and sink back down to their normal energy level. When they do this, the energy gets released in the form of light. But here’s the key thing about fluorescence – the wavelength of the light that gets emitted is actually longer than the wavelength of the light that excited the electrons in the first place.

This wavelength shift is what gives fluorescent materials their characteristic glow. Blacklights, for example, emit ultraviolet (UV) light, which has a very short wavelength and high energy. When those UV rays hit a white T-shirt, they excite the electrons in the fabric. As the electrons relax and drop back down, they emit visible light – usually in the purple or blue range. That’s why the T-shirt glows under the blacklight.

The Difference Between Fluorescence and Phosphorescence

Fluorescence is different from another shiny phenomenon called phosphorescence. Both work on the same basic principle of excited electrons emitting light, but the key difference is how long the electrons stay excited.

In fluorescence, the electrons get excited, emit their light, and then immediately drop back down to their normal energy level. This is why the glow from a fluorescent material stops as soon as the light source is turned off.

Phosphorescence, on the other hand, involves electrons that generally stay excited for a bit longer and burn their energy over time. This is what gives glow-in-the-dark paints and plastics their ability to continue glowing even after the original light source is gone.

The History of Fluorescence

We’ve known about fluorescence for a long time, actually way longer than UV lights have been a thing. The Aztecs were the first to notice it, observing that a medicine they used to treat urinary disorders had an opalescent glow.

In the 1800s, European researchers started experimenting with fluorescent materials and came up with various hypotheses about what was happening. In 1852, the physicist George Gabriel Stokes wrote extensively about the phenomenon and was the first to name it “fluorescence”, after his main study material – the mineral fluorite.

Fluorite definitely isn’t the only fluorescent material out there, but it was the one that opened our eyes to this fascinating property of light. And we’ve come up with tons of ways to take advantage of fluorescence in the centuries since.

The Many Uses of Fluorescence

The biggest and most obvious use of fluorescence is in fluorescent lights. That’s why they call them that! Fluorescent lights work by using an electric current to excite mercury vapor inside the tube, which in turn excites a phosphor coating on the inside of the tube. This phosphor then emits visible light through fluorescence.

But fluorescent lights are just the tip of the iceberg when it comes to the applications of fluorescence. Here are some of the other ways this phenomenon is being used:

Fluorescence Spectroscopy

Fluorescence spectroscopy is a technique that uses fluorescence to learn more about the physical properties of chemicals. By measuring how a material emits light after being excited, scientists can gain insights into things like the material’s structure, composition, and interactions with other molecules.

Fluorescence Microscopy

Fluorescence is also a major tool in biological research and medical imaging. Fluorescent dyes can be used to track and label specific biological molecules, allowing scientists to see inside cells and tissues in incredible detail. Some dyes even react to specific wavelengths of light, enabling researchers to look at multiple molecules at once.

This technique, known as fluorescence microscopy, has revolutionized fields like cell biology and neuroscience. It allows scientists to observe living cells and tissues in real-time, shedding light on fundamental biological processes.

Medical Diagnostics

Fluorescence is also being used in various medical diagnostic tests. For example, there are genetic tests where fluorescent dyes are used to label specific DNA sequences. If that DNA is present in a sample, the dye will bind to it and emit light when exposed to the right wavelength. This allows doctors to quickly and accurately test for the presence of certain genetic markers or pathogens.

Fluorescent compounds are even being used in some cancer surgeries to help surgeons determine if they’ve removed the entire tumor. And there are clinical trials exploring the use of topical fluorescent dyes to help detect tumors in the first place.

Fluorescent Imaging Agents

One fluorescent compound in particular, indocyanine green, has even been approved by the FDA for medical imaging purposes. When injected into a patient, it can bind to certain proteins and tissues, allowing doctors to see things like blood flow, organ function, and even the location of tumors.

Fluorescent Probes and Sensors

Fluorescence is also being used to create highly sensitive probes and sensors for a variety of applications. Fluorescent dyes can be designed to react to specific chemical or biological signals, allowing them to be used for everything from environmental monitoring to medical diagnostics.

For example, there are fluorescent sensors that can detect the presence of certain toxins, pathogens, or other analytes in a sample. The dyes emit light only when they interact with their target, providing a clear visual indication of what’s present.

Fluorite: The Crystal that Started it All

While fluorescence has many sophisticated uses today, it all started with a humble mineral called fluorite. This crystal, with its striking fluorescent properties, was the key inspiration and tool that allowed scientists to first understand and harness this phenomenon.

Fluorite is transparent to ultraviolet light, making it useful in the lenses and optics of many fluorescence-based technologies. Fluorescence microscopes, cameras, and telescopes often use fluorite lenses to better transmit and work with the UV light that excites fluorescent materials.

So the same mineral that helped us understand fluorescence is also integral to the tools and equipment we use to study and apply it. Fluorite truly is the crystal that opened our eyes to a whole new field of science and engineering.

Exploring Fluorescence with SciShow

If you’re a SciShow Rocks Box subscriber, you can get your own piece of this fascinating fluorescent mineral. Each month, the SciShow Rocks Box delivers a new mineral sample along with an in-depth look at its properties and uses.

Visit SciShow.Rocks to learn more about the SciShow Rocks Box subscription and how you can get your hands on some fluorite!

Whether you’re a mineral collector, a science enthusiast, or just someone who loves learning about the world around you, the SciShow Rocks Box is a great way to explore the incredible diversity of the Earth’s natural wonders.

And of course, you can always find the latest SciShow videos on a wide range of scientific topics on the SciShow YouTube channel. Be sure to subscribe to stay up to date on all the fascinating science stories covered by host Hank Green and the rest of the SciShow team.

Conclusion Why Things Look That Way Under a Blacklight

Fluorescence may seem like just a fun party trick, turning your white clothes neon under a blacklight. But this property of light has opened up entire fields of science and engineering, from medical imaging to biological research.

And it all started with a single mineral – fluorite. This crystal not only inspired the name “fluorescence”, but it’s also a key component in many of the technologies that use this phenomenon. Fluorite’s transparency to UV light makes it essential for the lenses and optics used in fluorescence-based instruments and devices.

So the next time you see something glowing under a blacklight, remember the humble fluorite crystal that kickstarted our understanding of this amazing property of light. Fluorescence may seem simple, but it’s had a profound impact on the way we see and study the world around us.