Night visual range: Difference between revisions

Latest revision as of 16:30, 25 April 2012

night visual range

(Also called nighttime visual range, transmission range.) The maximum distance at which a normal observer can see a particular point light source under given atmospheric conditions.

For a light source of luminous power P_v (in lumens), uniform atmospheric extinction coefficient σ along the viewing direction, and threshold illuminance E_thresh for the observer, the night visual range x is

Unlike the daytime visual range, the night visual range is determined by both the inverse-square law and atmospheric extinction. Note that for a light to be seen at a distance x > 0, its illuminance at the observer (P_v/x²) must exceed E_thresh. Even if σ is known, there is no unique night visual range because x also depends on P_v and the observer's dark adaptation.
See Allard's law

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-<div class="definition"><div class="short_definition">(<br/>''Also called'' nighttime visual range, transmission range.) The maximum distance  at which a normal observer can see a particular point light [[source]] under given atmospheric  conditions.</div><br/> <div class="paragraph">For a [[light]] source of [[luminous]] power ''P''<sub>''v''</sub> (in lumens), uniform atmospheric [[extinction coefficient]]  &#x003c3; along the viewing direction, and [[threshold illuminance]] ''E''<sub>''thresh''</sub> for the [[observer]], the night  visual range ''x'' is  <div class="display-formula"><blockquote>[[File:ams2001glos-Ne6.gif|link=|center|ams2001glos-Ne6]]</blockquote></div> Unlike the [[daytime visual range]], the night visual range is determined by both the [[inverse-square  law]] and atmospheric [[extinction]]. Note that for a light to be seen at a distance ''x'' &gt; 0, its [[illuminance]]  at the observer (''P''<sub>''v''</sub>/''x''<sup>2</sup>) must exceed ''E''<sub>''thresh''</sub>. Even if &#x003c3; is known, there is no unique night visual  range because ''x'' also depends on ''P''<sub>''v''</sub> and the observer's [[dark adaptation]]. <br/>''See'' [[Allard's law]]</div><br/> </div>
+<div class="definition"><div class="short_definition">(''Also called'' nighttime visual range, transmission range.) The maximum distance  at which a normal observer can see a particular point light [[source]] under given atmospheric  conditions.</div><br/> <div class="paragraph">For a [[light]] source of [[luminous]] power ''P''<sub>''v''</sub> (in lumens), uniform atmospheric [[extinction coefficient]]  &#x003c3; along the viewing direction, and [[threshold illuminance]] ''E''<sub>''thresh''</sub> for the [[observer]], the night  visual range ''x'' is  <div class="display-formula"><blockquote>[[File:ams2001glos-Ne6.gif|link=|center|ams2001glos-Ne6]]</blockquote></div> Unlike the [[daytime visual range]], the night visual range is determined by both the [[inverse-square law|inverse-square  law]] and atmospheric [[extinction]]. Note that for a light to be seen at a distance ''x'' &gt; 0, its [[illuminance]]  at the observer (''P''<sub>''v''</sub>/''x''<sup>2</sup>) must exceed ''E''<sub>''thresh''</sub>. Even if &#x003c3; is known, there is no unique night visual  range because ''x'' also depends on ''P''<sub>''v''</sub> and the observer's [[dark adaptation]]. <br/>''See'' [[Allard's law]]</div><br/> </div>
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