MadSci Network: Physics

Re: How Can I Test Sunglasses for Their Effectiveness in Blocking UVA and UVB

Date: Sun Sep 19 21:48:11 2004
Posted By: Michael Richmond, Faculty, Physics, Rochester Institute of Technology
Area of science: Physics
ID: 1095467925.Ph

I guess the answer depends on what you mean by "a relatively simple way." Let me try to provide some options.

First, I noticed a similar question in the MadSci archives. If you look at

you'll see what I consider a pretty complicated -- but very precise -- way to measure UV radiation. If you are handy with electronics, and can afford to order some pieces from manufacturers, then you might try this route.

On the other hand, if you want to go a simpler route, you might consider using good old photographic film. Some common types of film -- Kodak Tri-X, for example -- are even more sensitive to UV than to visible light. If you could find a set of color filters which block specific wavelengths of light, you could try to block all visible light. That is, you might use a red plus a green plus a blue filter to block all visible light ... but if the filters do allow some UV light to pass, then you could detect it with the film. Then you could place samples of your test material in the path of the light, too, together with the color filters, and see how much the response of the film changes. But this requires that you have a set of color filters with well-measured spectral blocking curves....

Another simple possibility is to use the bleaching properties of UV light. Many colors will fade when exposured to UV light. You could do some experiments by placing samples of different materials -- clothing, or colored PostIt notes, or samples of magic marker writing, or bits of painted wood, or strips of plastic -- out in the sunshine on a nice day. Compare each item to a second sample which you kept inside in the dark, and a third sample you placed inside, away from a window, but exposed to ordinary artificial lights. Any item which fades strongly in the sunlight, but not in the dark or the artificial light, is a good indicator of UV. Of course, you won't really have a good quantitative feel for the amount of UV light striking the object, but this is very easy and cheap.

Yet another, rather exotic, possibility is to use some form of life as your UV sensor. Some plants and some sea creatures require UV light to provide them with energy. I believe that some sea anemones, for example, have symbiotic little one-celled creatures within them which need UV radiation; that's why people who keep salt-water reef aquaria use special lights over their fish tanks. If you have lots of time and patience, you might try to find some small form of life which requires UV light, and cultivate several colonies of it. The amount by which the colonies grow might tell you about the amount of UV light.

In fact, that has just given me a better idea: you can use critters which are killed by UV as your sensors. I remember now that some forms of bacteria and other single- celled organisms are very sensitive to UV radiation. In fact, I believe that some water-treatment and sewage plants expose water to UV lights in order to sterilize it. I'll bet that you could do a very nice project by growing samples of some sort of organism in Petri dishes, exposing them to different types of light, and using the health of the colonies as an indicator of UV.

Those are my ideas. Gosh, I think I'd like to try that last one .... Good luck with your project!

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