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Torch Hunt: Find the Reflectors in the Dark

It’s dark in the garden. Sweep your torch around and look for the things that shine back at you. There are 8 to find, and one of them isn’t tape at all.

Hold the torch
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Move your mouse or finger over the garden. On a computer you can also click the garden and use the arrow keys.

The garden is an illustration, not a measurement. Real reflectors vary with the product, the angle, the distance and how clean they are.

What you’ve found

    Why the reflectors shine and the flowerpot doesn’t

    Most things, like a flowerpot or a football, scatter light in every direction, so only a little of your torchlight comes back to you. Reflectors are different. They send the light back towards where it came from. Hold the torch by your eyes and that returning light lands right in them, so reflectors look far brighter than anything around them.

    That’s why they fade when you switch to arm’s length. The light still heads back to the torch, but your eyes are now off to one side of it. The bigger the angle between the torch, the reflector and your eyes, the dimmer the reflector looks.

    Bike reflectors and prismatic tape do this with lots of tiny corner shaped prisms. Many reflective strips use tiny glass beads instead. To see the corner trick in action, and how scientists use the same idea to bounce lasers off the Moon, have a look at How Reflective Tape Works.

    Got a UV torch? Try UV Glow Hunt to see which things glow under ultraviolet light and which ones only shine back.

    Try it for real

    1. In a dark room, or outside at night with an adult, put something with a reflector on it a few steps away, like a bike, a school bag or a hi vis vest.
    2. Hold a torch right next to your eyes and shine it at the reflector. It should light up brightly.
    3. Keep looking from the same spot, but hold the torch out at arm’s length and point it at the reflector again. Watch it go dim.
    4. Ask a friend to stand beside you while you hold the torch by your eyes. You’ll see the reflector shine more brightly than they do.

    Never shine a torch into anyone’s eyes, and that includes pets.

    For teachers, clubs and parents

    Teachers, Scout and Guide leaders, clubs and bloggers are welcome to link to Torch 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.

    Torch Hunt is made by Flashback Tape, a UK supplier of reflective tape.

    Sources

    • Retroreflector, Wikipedia: the main types of reflector, how the viewing angle affects brightness, white reflectors and where reflectors are used.
    • Safety reflector, Wikipedia: where reflectors usually go on a bike.
    • What reflectors do, John S. Allen: dull and glossy surfaces compared with reflectors, and cube corner and glass bead designs.
    • Retroreflection, Photonics Dictionary: reflective tape on clothing, bikes and other objects.
    • Why do cat eyes glow in the dark?, Carnegie Museum of Natural History: the tapetum lucidum, and why human eyes don’t have one.
    • Cat’s eyes and the heiligenschein, University of British Columbia: why eyeshine heads back towards the light.