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<a accesskey="1" href="page.php?w=visibility&amp;p=6">1.Previous</a><br />
<a accesskey="3" href="page.php?w=visibility&amp;p=8">3.Next</a>
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<p>dangerous. The same can happen in a <a href="page.php?w=Dust_storm">sandstorm</a> or with <a href="page.php?w=forest_fire">forest fire</a>s.  </p>

<p><big>History</big></p>
<p><big>Derivation</big></p>
<p>To define visibility the case of a <a href="page.php?w=Black_body">perfectly black</a> object being viewed against a perfectly white background is examined. The <a href="page.php?w=Contrast_%28vision%29">visual contrast</a>, C<sub>V</sub>(x), at a distance x from the black object is defined as the relative difference between the light intensity of the background</p><p>
<a accesskey="1" href="page.php?w=visibility&amp;p=6">1.Previous</a><br />
<a accesskey="3" href="page.php?w=visibility&amp;p=8">3.Next</a>
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