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Shady business.

A simple experiment will tell you if your sunglasses block the sun's blinding ultraviolet (UV) rays.

We went out and bought ten of the coolest pairs of sunglasses we could find to try out this test. Some of them turned out to be great UV blockers, but some where real duds.

You can use the same test to see how your shades measure up. While you're at it, you can find out if sunglasses' labels really mean what they say. For example, does a label that reads "100 percent UV protection" mean that no harmful rays get through?

WHAT YOU NEED:

* sun-sensitive paper (available at craft stores)

* cardboard

* various pairs of sunglasses * a tub of water * hydrogen peroxide * a tablespoon * a sunny place (outside or on a windowsill)

WHAT TO DO:

1. Fill tub with water and 3 tablespoons hydrogen peroxide. Set aside.

2. Line up sunglasses to be tested. You can test about four pairs at a time.

3. Remove one piece of sun-sensitive paper from package. Keeping the colored side up, fold paper lengthwise and wrap sunglasses around it, as shown. (A piece of cardboard will help stiffen the paper.) For a 100-percent-UV-blocking control, cover a section of the paper with a small object that won't let any light through (e.g., a coin or a key).

4. Place the entire setup in direct sunlight. Leave for 1-5 minutes, until the paper fades to "white." (Use the same exposure time for each trial.)

5. Remove glasses and rinse paper in water and hydrogen peroxide bath for one minute. Dry flat.

6. Repeat Steps 3-5 for other sunglasses.

7. Compare prints left by test glasses to one another, to the control, and to the UV exposed background. The lighter the paper behind the shades, the better the UV protection. Record your observations in the data table.

Do you see any differences in UV-protection according to price level? Between plastic and glass lenses? Does lens color make any difference?

DON'T STOP NOW!

Try this experiment outside on an overcast day. Do clouds protect your eyes (and skin) from UV exposure? What would happen if you increased the exposure time?

Do non-tinted prescription glasses screen out UV rays? Try the experiment again to find out.

What other products could you test using UV-sensitive paper?
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Copyright 1993, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:experiment to see which sunglasses block out ultraviolet rays
Publication:Science World
Date:May 7, 1993
Words:383
Previous Article:Salt of the season.
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