UV or Not UV?: That Is a Question for Your Sunglasses

By Moyer, Richard H.; Everett, Susan A. | Science Scope, March 2014 | Go to article overview

UV or Not UV?: That Is a Question for Your Sunglasses


Moyer, Richard H., Everett, Susan A., Science Scope


How many pairs of sunglasses do you own? How do you decide which type to purchase? Choices range from dollar-store basics to high-end designer shades costing hundreds of dollars. Some people buy sunglasses for special purposes--for example, skiing, boating, or other outdoor recreational activities. Others own many pairs of inexpensive sunglasses in order to have some on hand at all times. You might also purchase prescription sunglasses. In addition, more and more people consider the health benefits of sunglasses, namely, how well they filter damaging ultraviolet (UV) light. 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).

In this 5E-learning-cycle lesson, students use UV-sensitive beads to test different sunglasses' lenses to determine their ability to filter UV light. UV-sensitive beads are white but change color when exposed to UV light and return to white when the source of UV light is removed. In A Framework for K-12 Science Education, the grade 8 endpoint for physical science requires students to recognize that "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" (PS4.B; NRC 2012, p. 135). This is essentially what sunglasses, like virtually all filters, do. Some of the light (including the UV portion) that strikes the lenses of sunglasses is reflected, some is absorbed (most of the UV portion), and the rest is transmitted through to the wearer's eyes. Sunglasses that are effective in protecting the eyes from UV light do so mostly by absorbing these harmful rays. UV radiation is that portion of the spectrum with wavelengths shorter than visible light. The longest wavelength of visible light (red) is 700 nanometers (nm), and the shortest is violet at 400 nm. Most of the ultraviolet radiation that reaches the Earth has wavelengths between 290 and 400 nm. This range includes what is referred to as UVA (320-400 nm) and UVB (290-320 nm) radiation. Most of the shorter wave-lengths are filtered by the atmosphere and do not reach the Earth's surface (Skin Cancer Foundation 2013a).

As students test different lenses, they will "evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem" (MS-ETS1-2; NGSS Lead States 2013, p. 61). In the United States, 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.

History

As early as the 1200s, the Inuit of North America cut thin slits into walrus ivory to make a type of snow goggle in order to reduce the Sun's glare off of the snow and ice (Canadian Muse-um of Civilization). One of the earliest references to sunglasses appears in 1750, when Englishman James Ayscough noted that when glasses were "a little ting'd with Blue, it takes off the glaring Light from the Paper, and renders every Object so easy and pleasant" (1750, p. 13). Not until the 1920s, however, did sunglasses become popular with the general public. In 1929, Sam Foster sold inexpensive sunglasses on the boardwalk in Atlantic City, a popular tourist destination (Foster Grant 2013), and they quickly became a national fad (Life 1938). In the 1930s, Edwin Land (the same person who developed instant film cameras) invented sheets for polarizing light, an invention that was then used in sunglasses in order to reduce reflective glare (Rowland Institute at Harvard). 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. …

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