Talk It Over

You cant see ultraviolet (UV) light. Its wavelengths are shorter than the light you see. But it can hurt your eyes. Sunglasses prevent ultraviolet from getting to your eyes. Do some sunglasses block UV light better than others?

Note: Do not use good sunglasses that you want to keep for this project. Removing the lenses from the frames will bend the sunglasses beyond repair.

Get

• Pliers
• Inexpensive or recycled sunglasses or glasses with tinted lenses
• Old pair of glasses with untinted lenses
• Transparent tape
• Pen or marker
• Glass cleaner and cloth
• Tray
• Sunprint paper*, 1 piece for each lens you test
• Sunny spot
• Water
• Access to a black-and-white photocopier
• Your grayscale (See "How to Make a Grayscale" in Part III.)

Go

1. Work indoors, out of sunlight. Ask an adult to use pliers to bend the frames on the glasses and remove one of the lenses from each pair you want to test.
2. Put a piece of transparent tape on a corner of each lens. Bend the tape back onto itself so no sticky sides are exposed. Write a number on the tape—a different number for each lens you want to test.
3. Clean each lens with glass cleaner and a clean cloth.
4. Place sheets of Sunprint paper on the tray—one for each lens you want to test. Put a number in the corner of each sheet to match the number tags you put on the lenses. Put each lens with the curved side down on its labeled paper.



5. Carefully carry the tray outdoors to a sunny spot. Make sure all the sheets are fully exposed to sunlight. No shadows anywhere!
6. Leave in the sun until the papers turn white—between 1 and 5 minutes. Take the papers indoors to a sink and rinse them in water for 1 minute.
7. Allow the papers to dry completely before you go on.
8. Place the papers on the black-and-white photocopier and make a copy. Compare the spots on the papers to your grayscale. From your grayscale, pick the number of the gray value that best describes the spot on your Sunprint paper.

Stay Safe

Handle lens and broken frames carefully. Sharp edges can cut you.

Go Easy

The "Go" procedure will work for you.

Go Far

Ultraviolet light changes chemicals in Sunprint paper. It changes the paper from blue to white. Then the water reacts with the changed chemicals in the paper, causing the white (exposed) areas to turn dark blue. Where UV was totally blocked, the paper turns white. Partial exposure to UV results in a shade of blue. The darker the blue, the more UV got through a translucent object, such as a lens. Try to relate your observations to the UV information given (sometimes) on the labels attached to sunglasses.

You might like to extend your investigation using a UV intensity meter and lens tester card*. Follow the directions on the card to measure UV levels in sunlight and the blocking ability of your lenses.

Another project might be a comparison of sunscreen creams and lotions. Smear small amounts of sunscreens with different SPF values on clear plastic. (SPF stands for sun protection factor. The higher the factor number, the greater the UV protection is supposed to be.) Place the smeared sheets over Sunprint paper and proceed as you did in "Go". Do the sunscreens live up to their advertising?

Show Your Results

Put gray values in a data table like this for "Go" and "Go Easy":

For "Go Far", make a similar table for the sunscreens you test, adding a column for the SPF on the product's label.

For all projects, display your Sunprints and your photocopies. Make a bar graph showing how the gray values of the spots compare. State brief conclusions and try to explain any differences you see.

Tips and Tricks

• You may need to adjust the light-dark setting on the photocopier until you get a good image that shows shades of gray clearly.
• Interpreting Sunprints can get confusing. Remember, the darker the spot, the more UV that got to it. A lighter spot (a lower gray value) means less UV reached the paper.

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CliffsNotes Parent's Crash Course Elementary School Science Fair Projects
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