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UV Glow Hunt: What Glows Under a UV Torch?

The lights are off in a spooky room. Eight things are hiding in the dark. Some only show up under a UV torch, and some only shine back under a normal white torch. Switch between the two and see what you can find.

Torch
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Move your mouse or finger over the room. On a computer you can also click the room and use the arrow keys.

The room is an illustration. Real colours and brightness depend on the torch, the material and how dark it is.

What you’ve found

    Glow or reflect? Two different tricks

    Fluorescent things glow. A UV torch gives out mostly ultraviolet light, which your eyes can’t see, so the room looks dark and a bit purple. Some materials soak up that UV and give it straight back out as a colour you can see, so they seem to glow. This is called fluorescence. It stops the moment the UV goes away, unlike glow in the dark stars, which keep shining for a while after the light is switched off.

    Reflectors shine back. Reflective strips don’t glow on their own. They send the torch’s light straight back towards it, so they shine brightly when the light comes from near your eyes. You can explore that in Torch Hunt and How Reflective Tape Works.

    Hi vis does both. The bright yellow fabric is fluorescent, so it turns some of the invisible UV in daylight into light you can see. The silver stripes are reflective, so they shine in headlights at night.

    Try it for real

    You’ll need a UV torch and a dark room, and an adult to help.

    1. Pour a glass of tonic water and a glass of tap water. Under ordinary light they look the same. Shine the UV torch on them and see which one glows.
    2. Write a secret message in yellow highlighter on white paper and look at it under the UV torch.
    3. Check a ripe banana, a white T shirt and a sheet of printer paper. Which ones glow?
    4. Now switch off the UV torch and shine a normal torch, held by your eyes, at a reflective strip on a coat or bag. It doesn’t glow under UV, but it shines back under the normal torch.

    Never shine a UV torch into anyone’s eyes, including your own and your pets’. Point it at the things you’re testing, not at faces.

    For teachers, clubs and parents

    Teachers, Scout and Guide leaders, clubs and bloggers are welcome to link to UV Glow Hunt or use it in lessons. It runs in the browser on phones, tablets and computers with nothing to download, and it doesn’t ask for names or save any scores.

    UV Glow Hunt is made by Flashback Tape, a UK supplier of reflective and UV reactive tape.

    Sources