Have you been wearing your sunscreen?  On a sunny day, see what kind of protection sunscreen offers with this easy experiment.

Materials

Black construction paper
Sunscreen (lotion, not spray – minimum SPF 30)

Procedure

1. Fold the paper in half.
2. Spread sunscreen on one side of the paper, but not the other.  Make a design if you like!
3. Leave the paper in a sunny spot for a few hours.
4. Observe the differences between the two sides of the paper.  Is the side with the sunscreen still dark?  What about the other side?

Keep the Experiment Going and Real World Application

If you have sunscreens of different SPF, test them out at the same time.

SPF stands for sun protection factor.  The sun emits ultraviolet (UV) light, which is invisible to our eyes and has higher energy than visible light.  Exposure to UV radiation causes sunburn, but sunscreen protects from UV rays.  The higher the SPF, the greater the protection.  The SPF is determined experimentally indoors by exposing human subjects, some wearing sunscreen and some not, to a light spectrum meant to mimic noontime sun.  The amount of light that induces redness in sunscreen-protected skin divided by the amount of light that induces redness in unprotected skin is the SPF.  For instance, SPF 15 sunscreen delays the onset of a sunburn in a person who would otherwise burn in 10 minutes to burn in 150 minutes.

Sources:
PBS
Sciencebuddies
Dermatology. About.com

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