Glowing Water: The Science of Fluorescence at Home (update 2025)
Educational and Fun Activities
Written by Gregg Payne
28 August 2024
🕓 10 min
What if you could make water glow with just a few everyday items? In this exciting at-home science experiment, we explore the fascinating world of fluorescence — the magical process where certain substances absorb invisible ultraviolet (UV) light and emit it as brilliant, visible colours.
Fluorescence isn’t just for glow sticks and parties. It’s a real scientific phenomenon found in nature, art, forensic science, and even medicine! Through this hands-on activity, children can learn how light, energy, and chemical reactions connect — all while making their own dazzling glowing water.
This 2025 updated guide will show you step-by-step how to create fluorescent water at home using safe, simple materials. Along the way, we’ll uncover how fluorescence works, where it appears in the natural world, and fun ways to extend the learning.
Ready to dive into some bright and brilliant science? Let’s get started!
1. What You’ll Need + Instructions
Before you begin, gather these simple materials:
✅ A clear glass or plastic cup
✅ Tap water
✅ A highlighter (yellow or green works best)
✅ Scissors
✅ UV or blacklight torch (widely available online)
Instructions:
Carefully open your highlighter and remove the ink-soaked felt inside. (Adult supervision recommended.)
Place the felt in your cup of water and gently squeeze it until the ink disperses into the water.
Stir the water lightly to mix.
Turn off the lights or move to a darkened room.
Shine the UV torch onto your cup — watch it glow!
The fluorescent molecules from the highlighter ink absorb the UV light and re-emit it as visible, glowing colours.
Optional: Try different colours of highlighter ink to see if they glow differently. Some pinks and oranges can create surprisingly bright results!
2. How Does Fluorescence Work?
Fluorescence happens when certain substances absorb energy from invisible ultraviolet (UV) light and quickly release it as visible light that our eyes can see. It’s a bit like catching invisible energy and bouncing it back as glowing colours!
Here’s what happens:
✅ UV light hits the fluorescent molecules (like the ones in your highlighter ink).
✅ These molecules absorb the energy and get excited, jumping to a higher energy state.
✅ Almost instantly, they relax back down, releasing the extra energy as visible light — creating that glowing effect.
That’s why you can’t see fluorescence without UV light. Regular light doesn’t have enough energy to trigger the glowing effect. UV torches, however, provide just the right kind of invisible energy.
Many natural and man-made materials are fluorescent — from minerals and fish scales to highlighter pens and glow-in-the-dark toys. Fluorescence is not only beautiful but incredibly useful in science, art, and medicine!
For another fun experiment with chemical reactions, check out our post Homemade Slime: A Polymer Experiment.
3. Exploring Fluorescence in Nature
Fluorescence isn’t just something we create in science labs or with highlighter pens — it’s a natural phenomenon found all around us! Many animals, plants, and minerals have evolved to glow under UV light, often for fascinating reasons.
✅ Coral reefs: Certain corals glow in brilliant greens, reds, and blues under UV light. Scientists believe this helps protect them from harmful sunlight or attracts helpful symbiotic organisms.
✅ Scorpions: These ancient creatures have a natural fluorescence in their exoskeletons, making them glow a ghostly blue-green under UV light. Scientists are still uncovering the reasons why!
✅ Fluorescent fish: Some fish deep in the ocean use fluorescence to communicate or camouflage themselves in dark waters.
✅ Minerals: Rocks like fluorite, calcite, and willemite glow in amazing colours under blacklight — giving geologists clues about their composition.
- Nature’s glowing secrets inspire scientists, artists, and engineers to discover new materials and technologies!
4. Fun Fact About Fluorescence
Did you know that some human teeth and bones naturally fluoresce under UV light? That’s right — a tiny bit of fluorescence exists inside us too!
The proteins and minerals in teeth and bones can absorb ultraviolet light and release it as a faint blue or green glow. It’s very subtle compared to glowing minerals or coral reefs, but it’s there. This discovery has important applications in forensic science, helping experts locate hidden evidence or understand ancient human remains.
Here’s another cool fact: scientists sometimes use fluorescent dyes in biology and medicine to make invisible structures visible. Under the right lighting, blood vessels, nerve cells, or even cancer cells can glow brightly — helping doctors and researchers learn more about the human body.
- Fluorescence isn’t just about glowing water or neon signs — it’s a hidden superpower woven into science, health, and even our everyday lives!
5. Tips for Success
Want your glowing water experiment to shine its brightest? Here are some handy tips to make sure everything works perfectly!
✅ Use a fresh highlighter: Older markers may have dried out, making the ink less vibrant. Newer pens give stronger fluorescence.
✅ Choose yellow or green ink: These colours usually fluoresce best because of their specific chemical structures. Pink and orange can work too but may be fainter.
✅ Ensure a dark environment: The darker the room, the more dramatic the glowing effect will be. Try using blackout curtains or doing the experiment at night.
✅ Get a good UV torch: Not all UV lights are equally strong. A dedicated blacklight torch will produce a clearer, brighter glow than a small keychain version.
✅ Experiment with quantities: If the water isn’t glowing enough, try adding a bit more ink or using less water for a stronger concentration.
Enjoy tweaking your experiment for maximum glow power!
Final Thoughts
Fluorescence is one of the most magical and surprising branches of science — and now you’ve seen it up close! By exploring glowing water at home, children gain hands-on experience with light, energy, molecules, and real-world applications of science they might encounter in nature, art, medicine, and beyond.
Experiments like this are a fantastic way to nurture curiosity, creativity, and scientific thinking from an early age. They show that science isn’t just something that happens in labs — it’s happening all around us, all the time!
To continue sparking your child’s love of discovery, explore The Science of Sound’s hands-on science workshops, exciting after-school clubs, and action-packed holiday camps. We use sound, light, and sensory exploration to make STEM unforgettable.
🔬 Visit scienceofsound.co.uk to find upcoming events — and keep the wonder of science glowing in your home and beyond!
