Fun with UV

UV (ultra-violet) light is invisible, which means you need more than your naked eyeball to do experiments with it. Our sun gives off light in the UV. Too much exposure to the sun and you’ll get a sunburn from the UV rays.

There are many different experiments you can do with UV detecting materials, such as color-changing UV beads and UV nail polish.

Here are a few fun activities you can do with your UV detecting materials:

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Materials:

• UV beads
• sunblock
• sunglasses
• sunlight
• clear plastic bag

Testing Sunblock You can test how effective your sunblock is at stopping harmful rays by slapping a coat of the lotion (or SPF-rated lip balm) on the beads and leaving them out in the sun for a minute. Bring the bead indoors and wipe off… did it change color? If so, then UV rays made it through the sunblock to your bead, and chances are that your sunblock isn’t doing it’s job. Does it matter how thick of a coat you layer on?

You can alternatively place the beads inside a plastic bag and coat the outside of the bag with sunblock. And is the sunblock really waterproof? Meaning that they still are white after dunking the beads underwater while sunblocked…?!

Different Times of Day Stick the UV beads outside and take note how bright the colors are in the morning, noon, and afternoon.  You’ll notice a big difference depending on the sun’s spot in the sky. Does it matter whether it’s sunny or cloudy?

Absorption and Filtration Test out different lenses and filters to see which block UV light.  Lay a handful of beads on the sidewalk and set a pair of sunglasses in top (lenses sitting on the layer of beads).  Did any UV light make it through?  If it didn’t, your beads should stay white. What other things can you test? (Hint: how about inside your car?)

 
Download Student Worksheet & Exercises

Why does that work? UV sensitive materials have a pigment inside that changes color when exposed to UV light from either the sun or lights that emit in the 350nm – 300nm wavelength.  (UVA is high-energy: 400-320nm, and UVB is low energy: 320-280nm).  If you have fluorescent black lights, use them.  (Do regular incandescent bulbs work? If not, you know they emit light outside the range of the beads!)

When light hits the pigment molecule, it absorbs the energy and actually expands asymmetrically (one end of the molecule expands more than the other).  Different expansion amounts will give you a different color. Although it’s a bit more complicated that that, you now have the basic idea. Your beads will change colors thousands of times before they wear out, so enjoy these super-inexpensive UV detectors!

Exercises

1. What kinds of light sources didn’t work with the UV beads?
2. Did your sun block really block out the UV rays?
3. Which was the best protection against UV rays?

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