Science Buddies: "Ask an Expert"

hi.
I'm doing a project to test Which brand of spf 30 sunscreen protects the skin from everyday sunshine.
i decided to test my aim by equally measuring each sunscreen and applying it on photo film and since photo film when in light changes from dark to light. I thought by placing the sunscreen on the film i would be able to see, after scrapping the sunscreen off the film, which one out of the ten different sunscreens keep the film the closet to the original colour it started with. But this didn't work
please can you help me find out what i must rather use to replace the film aspect in our science project.

Photographic film is going to respond to all visible light, so what you're saying isn't a big surprise. A number of other sites on the web talk about doing this with an electronic UV meter like you might take to the beach on a sunny day. I can't specifically recommend any, but they tend to look like this one: http://www.amazon.com/dp/B000EPYMDW

You would put it in a box, covered by a sheet of glass and put the sunscreen on the glass. Read the meter, clean the glass off completely and try another sunscreen. Don't forget to do trials with clean glass as a control.

Howard