Sunscreen experiment suggestion?

Question

I'm looking for a simple basic experiment for my kids to test whether something blocks UV rays or not (whether it might be a sunscreen). Short of using human skin (and burning) is there anything else that can be tested? Just for response to UV light. I thought of using construction paper because it fades in the sun. Cover one section with a t-shirt, another with glass, put sunscreen lotion on another and see which fades first. Can anyone else come up with something better? It's OK if we'd need to purchase some items.

Answer 1

um UV is scattered by glass...so that won't work.

oh, opps. i mis-read your question (i thought you were going to put lotion ontop of the glass). well...how are you going to deal with the lotion wetting the paper? it seems like you'll have to run this experiment for a "long" time to see the effects.

check out these experiments:
http://www.stevespanglerscience.com/content/experiment/00000134

http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/how-does-sun-cream-work/

Answer 2

Why not human skin? On your left arm and fingers, keep sunscreen on some, wear a bracelet made from an old t-shirt, etc. Take before-and-after photos.

You'll need a little more research on how to test just the UV part of the spectrum. Just your luck, construction paper might not be sensitive to UV. See if you can cover your whole experiment box with a filter that transmits UV but blocks everything else.

For a faster response, try a pair of glasses with photochromic lenses.

Answer 3

There are some t-shirts that used to be sold, which were printed with a photo-active dye. The effect was any writing on it turned from yellow to red (or was it the other way around?) when exposed to sunlight. But this is not practical to be hunting for such a t-shirt.

Try instead to get the colorants from orange/red vegetables. They are usually carotenoids, which will isomerize (change shape) when exposed to UV light, and the color changes too (bleaches) when this happens. I suggest pureeing the vegetable in a blender (if you use tomatoes, don't put the seeds), then blotting the mash with paper kitchen towels to color the paper.

Cover the blotted paper with polyethylene (sandwich bag, clear and colorless) and apply the different sunscreens to the outside of the plastic. Have one piece of blotted paper in a a platic bag, but covered with foil, just as a "control" (other things, like heat or reaction with oxygen in the air, will also change the color of the carotenoids). Put all your samples in a sunny place (including the control).

I haven't tried this myself, so it may not work after all. Polyethylene itself blocks some UV, but I can't think of an inexpensive, everyday material that doesn't block UV. (Glass blocks UV. In the laboratory, we need quartz windows for such experiments.)

P.S. I _have_ observed the color of paprika in oil (sausage drippings) disappear within a day because of light exposure, so this experiment should be do-able within a day or two.

Answer 4

Perhaps you can use a plant: cover some leaves or a section with sunscreen and others without and compare the color of the leaves at the end of whatever period of time you wish. The differences in darkness of green of the leaf/chlorophyl production should be easily linked to the blockage/lack of blockage of sunlight. As the experiment calls for UV rays, using high intensity light should do the job. I hope this helps.