Materials List

Each group needs:

• 1 square of UV photo-sensitive paper, such as Sun Print UV paper, approximately 4" x 6", which is a special paper that changes color in sunlight depending on how much UV light to which it is exposed; it is sold in 8" x 12" sheets, so you can cut them in half; available at https://www.amazon.com/SunPrint-W330-Paper-Kit/dp/B001KOGY3M

• 1 piece of glass or transparent plastic that is at least as big as the UV paper; overhead transparencies and plastic wrap work well

• 1 strip of opaque paper that is 1" x 6"; 4" x 6" index cards work well

• 1 office file folder, to keep the photographic paper in before exposing it to sunlight

• 2-3 cotton balls

• 1 small strip of index card to evenly spread the sunscreen; a straw works also

• pan of water, big enough to hold the square of photo-sensitive paper

Materials that may be shared with the entire class:

• 4 (or more) different SPF value sunscreens of a broad range; ideally, the SPF values increase in equal increments to facilitate a quantitative analysis at the end (for example: 2, 4, 6, 8 or 5, 10, 15, 20); lower SPF values for sunscreens and tanning oils work best

Procedure 

Before the Activity

• In a dark room, prepare the materials by cutting the UV paper and the 1" strips down to size for each group. Place each paper in a file folder to keep the paper unexposed until the students are ready to collect their data.

• If possible, arrange to have the students complete this activity in the middle of the day, when the sun is at its highest point.

With the Students

1. Have each group collect its materials (except the UV paper). Direct students to use a cotton ball to deposit a 1-2" diameter circle of each of the various types of sunscreen or tanning oils onto the plastic. Use the small piece of index card to spread the sunscreen into an even layer. You can fit 4-5 different sunscreens on the same piece of plastic. Refer to the diagram on the worksheet.

2. Ask students to write down a hypothesis about which area (that is, which sunscreened spot) they expect will be the most protected.

3. Move the entire class outside into a sunny area. Give each group a folder containing one piece of UV paper. Remind students to keep the UV paper in the folder until you tell them to take it out. Then they should carry their plastic piece on top of the file folder, holding it level as they walk.

4. Explain this next step in advance, so that students can complete it correctly. It might be worthwhile to practice the steps with a blank sheet of paper, so that mistakes are minimized once the UV paper is exposed. Have students refer to the diagram on the worksheet.

• • When ready, remove the UV paper and place the plastic piece directly on top of it. Place them in direct sunlight. The dark side of the paper should be the side that makes contact with the plastic sheet. The paper should change color or intensity as it is exposed to light. Expose the paper for 5 minutes.

  • During these same 5 minutes, perform a control test. Take an opaque slip of paper that covers the top of the UV paper. Every minute, move the slip of paper about 1 inch to the right. This exposes the paper in a systematic way, giving students comparison sunscreen samples.

5. Once the exposure is complete, move the project back inside. To stop further exposure of the UV paper, place it in a pan of water (so that it is completely submerged). The image may completely disappear and then reappear. Depending on the type of paper, the image will be completely inverted after soaking in the water. Leave the image in the water for 3 to 5 minutes. Remove the UV paper from the water and let it dry.

6. Ask students to record observations as to the color differences between areas protected by the various lotions/oils. Then have them make a bar graph of the results. It may help to do make the first bar on the graph as a class. Have students look at their lowest SPF value. How does that exposed area compare to the control strip on top? Is it closest to the 1 min exposure, or somewhere else? Ask them to estimate about how long of an exposure to which it is equivalent. Once they have identified the equivalent exposure time, have them make a vertical bar on their graph to that point.

7. Ask students to evaluate the quality of their data, as the last step on the worksheet.