Spotting the Invisible
The Explorers spent a session in October 2012 investigating invisible light. Just because we can’t see it doesn’t mean it can’t affect us—and with some cleverness we can force the invisible to reveal itself. Indirectly, at least!
Everyone has seen a rainbow, and many are familiar with the “Roy G. Biv” nickname that helps us memorize the order of the colors (red, orange, yellow, green, blue, indigo, and violet). What many don’t realize is that those colors actually come from—and form—white light. A rainbow is nature’s way of splitting the white sunlight into all of its component colors. We can do the same thing with a prism, a triangular-shaped piece of glass that separates the white light into colors just like water droplets suspended in the sky do when we see a rainbow.
The scientific name for this band of color is the “visible light spectrum.” Each color is really a form of energy, with the color that we see being determined by the wavelength (literally, the distance from one wave peak to the next) of the energy. Visible light with the longest wavelengths appear red, while those with the shortest wavelengths look blue and purple.
The coolest part, though, is that what we see—the colors—are just a tiny part of the whole “electromagnetic spectrum.” There are far longer and shorter wavelengths of energy than what our eyes can perceive—our eyes have just developed to be most sensitive to the part of the spectrum that we “see” because those are the energies where our sun’s light is at its peak. There are lots of other types of “light” that are literally invisible to our eyes.
Energy with slightly longer wavelengths than our eyes can see (just to the side of the red on a rainbow) is known as infrared. Even longer wavelengths are known as microwaves and radio waves. At the other end, shorter and shorter wavelength energies go beyond the blue end of our rainbow—these are known as ultraviolet, x-rays, and gamma rays. One tricky thing to keep in mind is that the shorter the wavelength, the stronger the energy—so ultraviolet is more energetic than visible light, for example, while x-rays are even more so.
It is ultraviolet light that the Explorers focused on in this meeting. Being stronger, ultraviolet light is able to penetrate our skin more than visible light—which leads to the fact that it is ultraviolet light that causes sunburns (and even some types of skin cancers). How do you protect yourself from this energy that you can’t even see? By applying a protective coating of a substance known as a sunscreen. Sunscreens work by blocking these ultraviolet (or UV) rays, and different levels (“sun protection factors,” or SPF) of sunscreen block more or less of the rays.
Our question was, how can we detect UV light that we can’t actually see? (Short of lying out in the sun until we burn, that is!) The answer came in the form of small, nondescript-looking little white beads. These UV beads are actually sensitive to the ultraviolet rays, and when exposed to sunlight quickly turn a variety of colors. Very nifty.
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The Explorers performed an experiment (which could easily be adapted for a science fair project) using the beads, some Ziploc baggies, and different SPF levels of sunscreen. We smeared the different types of sunscreen on different baggies and then tossed in some beads. Taking them out into the sunlight, we then observed the variation in how much each bag of beads changed color. If the SPF numbers were on the up and up, we should have observed that beads inside a baggie smeared with a high number would stay fairly pale in color, while those inside a bag smeared with a low number would show much more intense colors. Happily this is what we saw, although Mr. Ramsey did say that in other years this has not always been the case—making us wonder if all brands of sunscreen are truly as effective as they claim. Hey, there’s that science fair project just begging to be done!
Finally, it was time to turn this experiment into some wearable works of art, as each student took a handful of beads and some string to make themselves either a bracelet or necklace. Who says science can’t be useful AND pretty at the same time?
Check out the photo gallery for some pictures of our UV beads activity (although not as many as we would have liked, since Mr. Ramsey’s camera bit the dust before we were finished), and click on the link below to see more information from a previous year’s meeting with these beads.