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Activity Number 21 - Made In The Shade
Purpose
To show the importance of reducing direct UV exposure, and to illustrate the degree of protection provided by various sources of shade.
Materials
- UV meter
- pencil and pad
- calculator
Method
- Take the UV meter outdoors near noon on a sunny day in April through September. Best results will be achieved in May or June.
- Record the UV reading obtained under a variety of conditions; for example:
- direct sunlight
- full shade, e.g. beside a building or under a group of trees
- partial shade, e.g. under a single, small tree
- portable shade, e.g. under a beach umbrella
- Calculate the percentage of UV transmitted through each type of shade, compared to the full sun reading.
- UV transmitted (%) = (shade reading ÷ full sun reading) x 100 percent
- UV reduction (%) = 100 percent - UV transmitted
Observations
UV reductions will vary with your particular circumstances, but for UV, all shade is not created equal. Different degrees of shade can reduce UV exposure by roughly 60 to 95 percent.
Conclusions
The more of the sky around you that is blocked by trees and other objects, the lower the amount of UV reaching you. Conversely, the more open sky visible around you, the higher the UV, because the atmosphere scatters UV rays so effectively. Therefore, UV under a group of trees, for example, is lower than under a single beach umbrella.
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