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am doing a science fair project that envolves testing weather or not the sunscreen in make-up works as well as regular sunscreen. I take some Photosensitive Paper (black paper that turns white when exposed to the sun), put regular sunscreen on one piece, and the liquid makeup foundation (with the same SPF as the regular sunscreen) on another different piece. I label both pieces, and then expose them both to the sun for exactly 2min 30sec. Since the Photosensitive Paper is black, and it turns white when it is exposed to the sun, the sunscreen or the foundation will (or should) block the sun from getting to the paper, leaving the part where the sunscreen or foundation was black, because the sun wasn't exposed to it. I am curious, since it is winter, and it is cloudy and cold where I live (Colorado) if the weather will effect this experiment. Will the clouds block the passing of UV rays?
So-
You think that it will be O.K. to do the project today? I live in Colorado, and it is Cloudy and 38 degrees farenheit today. I'm not sure if the weather is going to get any better. Would it really make any difference if I did it today, rather than some other time on Christmas Break?
In addition to my other question, I was wondering if higher SPF in a sunscreen just gives you longer sun protection, or better sun protection?
PLEASE!!!!! I NEED HELP! A S A P!!!!!!
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hzatz
- Former Expert
- Posts: 15
- Joined: Wed Nov 17, 2004 12:09 pm
A few answers to a few questions...
Comparing sunscreens is a clever idea. Unfortunately, there are a number of complications involved.
First of all, you need to be sure about what it is you're actually measuring. Light is made up of a spectrum of frequencies--not just the colors of the rainbow, but all sorts of different "colors" of infrared, ultraviolet, and other frequencies. Your photosensitive paper is likely to react to some combination of these frequencies--for example, it might change colors if exposed to red or green light, but not blue. Similarly, the various makeups and lotions will block some frequencies of light, but not others.
What you'll end up seeing with the paper is a combination of what colors of light are actually present, what colors of light are blocked by the makeup, and what colors of light the paper is sensitive to.
Given all of that... clouds will block some UV rays, just as they block the rest of the light coming from the sun. If you can spend the time to figure it out, probably the best thing to do is to expand your experiment a little bit. See how your photosensitive paper reacts differently under different light sources. Try different colors of light bulbs... or maybe even a black light bulb, which mostly emits UV rays.
SPF is a measure of what fraction of the UV light at a particular frequency range--more or less the UV frequency range that causes sunburn, if the manufacturers are doing their job right. SPF 2 means 1/2 of the light from that range gets through; SPF 40 means 1/40th of the light. So, if the lotion doesn't get wet or rub or wash off, the protection would be both better and longer.
If you try to do a google search on SPF lotion or UV-A vs. UV-B (different kinds of UV light for suntan and sunburn, more or less), you may find some useful background information. Try http://www.fda.gov/fdac/features/2000/400_sun.html, for example.
So, sure, go ahead and try the project today.
First of all, you need to be sure about what it is you're actually measuring. Light is made up of a spectrum of frequencies--not just the colors of the rainbow, but all sorts of different "colors" of infrared, ultraviolet, and other frequencies. Your photosensitive paper is likely to react to some combination of these frequencies--for example, it might change colors if exposed to red or green light, but not blue. Similarly, the various makeups and lotions will block some frequencies of light, but not others.
What you'll end up seeing with the paper is a combination of what colors of light are actually present, what colors of light are blocked by the makeup, and what colors of light the paper is sensitive to.
Given all of that... clouds will block some UV rays, just as they block the rest of the light coming from the sun. If you can spend the time to figure it out, probably the best thing to do is to expand your experiment a little bit. See how your photosensitive paper reacts differently under different light sources. Try different colors of light bulbs... or maybe even a black light bulb, which mostly emits UV rays.
SPF is a measure of what fraction of the UV light at a particular frequency range--more or less the UV frequency range that causes sunburn, if the manufacturers are doing their job right. SPF 2 means 1/2 of the light from that range gets through; SPF 40 means 1/40th of the light. So, if the lotion doesn't get wet or rub or wash off, the protection would be both better and longer.
If you try to do a google search on SPF lotion or UV-A vs. UV-B (different kinds of UV light for suntan and sunburn, more or less), you may find some useful background information. Try http://www.fda.gov/fdac/features/2000/400_sun.html, for example.
So, sure, go ahead and try the project today.
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Laura
Thanks for the info, but I tried the science fair project today, and I really don't think it worked. 
I think the sunscreen and the make-up seeped into the photosensitive paper, and when we tried to get it off so we could see which product worked better, the color of the photosensitive paper was the same color as the makeup or sunscreen. Do you think we might have gotten the wrong kind of paper?
I think the sunscreen and the make-up seeped into the photosensitive paper, and when we tried to get it off so we could see which product worked better, the color of the photosensitive paper was the same color as the makeup or sunscreen. Do you think we might have gotten the wrong kind of paper?
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hzatz
- Former Expert
- Posts: 15
- Joined: Wed Nov 17, 2004 12:09 pm
Let's see...
You could avoid gooping up your photosensitive paper by putting something transparent and water-tight between it and the makeup. For example, you could try putting the makeup on plastic wrap or a small piece of glass in front of the paper.
You probably also need a control for your experiment--for example, you could see what happens to a piece of photosensitive paper with no makeup.
But remember from my earlier comments--the paper might not be sensitive to whatever frequency is blocked by the makeup. If that's the case, the makeup won't make any difference...
You could avoid gooping up your photosensitive paper by putting something transparent and water-tight between it and the makeup. For example, you could try putting the makeup on plastic wrap or a small piece of glass in front of the paper.
You probably also need a control for your experiment--for example, you could see what happens to a piece of photosensitive paper with no makeup.
But remember from my earlier comments--the paper might not be sensitive to whatever frequency is blocked by the makeup. If that's the case, the makeup won't make any difference...
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Guest
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Laura