Problem: What is the power flux of light whose intensity is 5.3 watts/m ^ 2 through a circular window with radius 5.6 meters, if the sunlight is perpendicular to the plane of the window?
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Solution: The area of the window is `pi ( 5.6 m) ^ 2 = 98.47 m ^ 2, so the flux of a perpendicular 5.3 watt/m ^ 2 beam will be ( 5.3 watts / m ^ 2)( 98.47 m ^ 2) = 521.8 watts.
Generalized Response: The power flux of an energy intensity `intensity (typically measured in Watts/square meter) intercepted at a perpendicular by an area A is just flux = `intensity * A (and will typically be a power intensity in Watts).
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