Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. A half sheet of sun print paper is required by each student team. Cut the sun print paper sheets in half prior to class. Cut enough sheets for each team. It is best to carry out this step in very reduced light away from any UV light or sunlight.
2. Cut enough 1" x 2" acetate strips so that each student team will have three.
3. Cut a 1" x 2" black construction paper strip for each student team. The paper should be thick enough to block out all sunlight.
4. Obtain a variety of sunscreens with varying SPF ratings, or have students bring in their own samples from home. Try expensive brands and generic brands for comparisons.
5. Cut pieces of corrugated cardboard into 4" x 6" sheets. Use old boxes or have students bring some from home.

Safety Precautions

Warn students about the dangers of burning the retina of the eye if there is direct exposure to UV light from the Sun. Wash hands thoroughly after working with sunscreen lotions to avoid getting any in eyes. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The developed sun print papers can be kept in student notebooks indefinitely. The other materials can be disposed of in the trash following Flinn Suggested Disposal Method #26a.

Teacher Tips

• Enough materials are provided in this kit for 60 trials of the experiment. This ample supply of materials will allow for student errors and additional investigations as discussed on the SPF Worksheet. The lab can be completed in one 50-minute class period.

• Reduce classroom light to an absolute minimum during the setup phase of this laboratory. Do not complete the setup phase in sunlight or other bright lights.
• This lab should be completed on a sunny or near-sunny day. Sunlight is required to expose the sun print paper in step 5 of the Procedure.
• If supervision out-of-doors is an issue, organize the trip so that all can leave together and return together. The entire outdoor portion of the lab should take only 5–10 minutes.
• As an extension have students test the difference between sunscreen, sun block and suntan lotion.

Sample Data

Answers to Questions

1. Why was the strip of black construction paper included in this experiment?
   

   The black strip acts as a “control” to show the result of complete screening and to serve as a basis for comparison.
   

2. Use the results of the sun print paper above to discuss the relationship between the SPF number of a sunscreen and its ability to screen for UV radiation.
   

   The higher the SPF number the more UV light is screened out and thus the less exposure of the sun print paper. Student results might vary.
   

3. Describe an experiment using sun print paper that might demonstrate the relative effectiveness of different brands of sunscreen.
   

   Answers will vary but should include testing different brands all with the same SPF rating.
   

4. Describe an experiment using sun print paper that might prove or disprove the following statement: “Sunglasses are better filters of UV light than are sunscreens.”
   

   Answers will vary but might include exposing sun print paper through sunglasses and comparing it to the highest SPF sunscreen available.

Introduction

Do sunscreens really work? What does SPF mean? Are the ratings accurate? Do sun lotions without an SPF rating offer any protection?

Concepts

• Sun Protection Factor (SPF)

• UVB radiation
• UVA radiation

Background

Exposure to ultraviolet (UV) radiation has been linked to a number of human health problems, including sunburn, skin cancers, premature aging of the skin, cataracts and alteration of the immune system. UV radiation penetrates the Earth’s layer in two wavelength bands, UVB (290–320 nm) and UVA (320–400 nm). UVB rays are higher in energy and act directly on biological molecules causing skin cancer, aging and the familiar delayed sunburn. In contrast, the lower energy UVA rays act more indirectly, causing an “immediate” sunburn that diminishes within several hours after exposure. Concern about the adverse effects of UV radiation exposure has led to the development of sunscreens to block the UV radiation. These sunscreens work by absorbing the UV radiation and dissipating the absorbed energy as heat before it can damage biological molecules.

The rating system for sunscreen protectors was developed in the 1970s. SPF (Sun Protection Factor) is a rating developed for indicating the relative effectiveness of a product to provide protection from UVB radiation. Protected skin is compared to unprotected skin with controlled amounts of sunscreen applied and the derived ratio reflects the relative effectiveness of the product. The higher the SPF number the more effective it should be in blocking UVB radiation.

Sun print paper is a chemically impregnated paper that turns various shades of color depending upon the amount of exposure to UV radiation. Varying the amounts of exposure of the paper will result in varying color intensities of the developed paper. Sun print paper can be used, therefore, to test the ability of a sunscreen product to screen out UV radiation.

Materials

Safety Precautions

Ultraviolet rays are damaging to the eyes. Never look directly into the UV light or Sun. Follow all laboratory safety precautions.

Procedure

1. Indoor daylight or incandescent light will not damage the sun print paper if the exposure time is short. Read all of the directions for this laboratory. Become familiar with the entire procedure so that work can proceed quickly once the sun print paper is removed from its storage container.
2. Select the three sunscreen products to be tested. Record their brand names and SPF ratings on the SPF Worksheet. Use a clean glass stirring rod to smear a thin layer of one of the sunscreens evenly over the surface of an acetate strip. The side of the stirring rod works well for this. Clean the stirring rod with water, dry, and repeat the procedure with a different sunscreen and acetate strip. Repeat this procedure for a third product on a third acetate strip. Be sure to keep track of each strip and its SPF identity.
3. Use four pins to attach a piece of sun print paper to a piece of corrugated cardboard.
4. Use eight other pins to place and hold the three pieces of sunscreen-coated acetate onto the top of the sun print paper (sunscreen side up). Also pin a piece of thick black construction paper onto the top of the sun print paper (see Figure 1). Be sure to note the positions of the different samples so that the results can be correlated once the acetate sheets have been removed.

5. Fill a bowl with water.
6. When the preparation is complete, take the entire cardboard setup outside and place it in the sunlight. Expose the sun print paper for 1–2 minutes if the sunlight is bright and up to 5–6 minutes if the sky is overcast. Expose until the sun print paper around the pinned items turns a pale blue. Do not overexpose the paper.7. Quickly return to the classroom and remove all the pins and the sun print paper from the corrugated cardboard.
7. Immediately soak the sun print paper in the container of water for about one minute. This will develop the sun print paper and make the exposures permanent.
8. Remove the paper from the water. Let it drip dry for one minute. Lay the paper flat on the corrugated cardboard again and pin it in place and let it dry. The images will sharpen during the drying time.
9. Allow the paper to dry completely. (Overnight drying may be required.) When the paper is completely dry, remove it from the cardboard and tape it to the SPF Worksheet in the space provided.
10. Examine the results on the sun print paper and then answer the questions on the SPF Worksheet.
11. The developed sun prints can be attached and saved on the SPF Worksheet.

Student Worksheet PDF

10327_Student1.pdf