|UV or not UV?
That is the question for your sunglasses
Developing and Using Models
Team Members: ________________________________________________________________________________________________________________________________________________________________________________________________________________
Define the Problem: According to the U.S. Environmental Protection Agency, “Long-term exposure to UV radiation can lead to cataracts, skin cancer around the eyelids, and other eye disorders” (2010, p. 1). When light shines on an object, it is reflected, absorbed, or transmitted through the object, depending on the object’s material and the frequency (color) of the light. The engineering challenge is to
design a pair of sunglasses that will decrease the amount of UV light that enters the wearer’s eyes. UV-protective sunglasses are a spin- off of NASA research at the Jet Propulsion Laboratory from the 1980s, where scientists studying birds of prey discovered that the birds produced an oil that protected their eyes from UV light. This research was first applied to the design of equipment for shielding welders’ eyes and, ultimately, sunglasses (NASA 2011).
Criteria and Constraints: There are voluntary standards for sunglasses administrated by the American National Standards Institute (ANSI). The criteria in the ANSI standards require that sunglasses filter out essentially 99% of the UV light below wavelengths of 400 nm, allow colors to be perceived accurately, and are impact resistant.
Materials: Throughout this challenge, you will use UV beads—small plastic beads that have been treated so they change color when exposed to UV light; sunglass lenses; egg cartons; medicine vials; tape
What are some different ways that people protect themselves from the Sun? Share these ideas with your classmates. (Google docs)
Your teacher will provide you with a white plastic bead that is sensitive to certain types of light. Place your bead in a sunny window for about a minute, less if you notice a change in the bead’s color. Record your observations. (same Google doc)
Remove the bead from the window and hold it in your hand so that it is no longer exposed to any light for about two minutes. What happens to the bead after it has been removed from the sunlight near the window? Record your observations. These beads are sensitive to the ultraviolet (UV) light that is a part of sunlight. UV light, however, is invisible to your eyes. Therefore, the change in color of the beads serves as an indicator of the presence of UV light.
4. You need to construct a testing apparatus so that the only light that reaches the UV bead must pass through the lens. You also need to make sure that the beads do not get exposed to UV light until you are ready to conduct a test. One method is to place a UV bead in one of the single egg holders from an egg carton. Fold over a piece of tape to secure the bead to the center of the egg holder. Cover the opening with the lens from one of the sunglasses you wish to test and then use duct tape to seal around the lens.
5. Tape a second UV bead into an egg holder without a lens attached and then hold each in the Sun with both pointing directly at the Sun for one to two minutes. Do not look at the Sun directly while doing this part of the activity.
6. Return to your work area away from any direct sunlight and quickly unseal the egg holder and compare the color of the two beads. Record your observations in a table like the one shown below and repeat for two other lenses. Be sure to start each test with a fresh white UV bead. (re-create the table in your Google doc)
Analysis questions: (same Google doc)
Which lens resulted in the darkest color change of the bead? The least?
Share your results with your classmates.
What does the amount of color change mean? Would a darker or lighter bead indicate a better lens to protect your eyes from UV light? Explain.
How do the lenses compare? Explain.
You know that UV light is harmful to your eyes and that some sunglasses are able to filter most of the UV light that passes through them. How might UV light enter your eyes even if you are wearing sunglasses? Record your ideas. (same Google doc)
Test a lens in the same way as above but without sealing it to the egg holder with tape. You will need to hold the lens in place while pointing it at the Sun. After one or two minutes, return to your work area and observe the UV bead and record your observations. (same Google doc)
Compare these results with the tests when you sealed the lens to the egg holder. Which test better represents how people actually wear sunglasses? (same Google doc)
Your engineering challenge is to design a pair of sunglasses that will decrease the amount of UV light entering the wearer’s eyes.
Examine the glasses your teacher provided to determine their design weaknesses that allow UV light to enter the wearer’s eyes. Brainstorm ways the sunglasses could be modified to address these design weaknesses. Make a sketch of your improved sunglasses, labeling your changes. Explain (write a rationale – use data as support) how your design better protects the eyes from UV light. (same Google doc)
Extend the design challenge:
There are many other things besides your eyes that can be damaged by exposure to UV light. One example is medication that is often sold in small plastic bottles. Design a procedure to test if different types of small bottles filter UV light. After your teacher has approved your plan, carry out your testing. Record your results and explain your findings. (same Google doc)