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## [TowerTalk] Acuity

 To: [TowerTalk] Acuity bhorn@hornucopia.com (Bruce Horn) Thu, 18 Mar 1999 08:47:42 -0800
 ```Visual acuity varies with light intensity. The retina of the eye is composed of two types of receptors: rods and cones. Cones function well in bright light and produce color vision, but are relatively blind at low light levels. Rods function well at low light levels, but are relatively insensitive to color. For daytime light conditions, the best visual acuity will occur for objects in the center of the field of view. For dim light conditions, the best acuity occurs for objects about 20 degrees off axis (high concentration of rods). For discerning a high contrast object from a uniform background in daytime, the average human could detect an object as small as 0.003 inch at 1 foot (or 3/16 inch at 62.5 feet). However, for objects of less contrast (maybe more like a guy line against sky), the average human would be limited to about 0.01 inch at 1 foot (or 3/16 inch guy line at 18.8 feet). However, under dim light conditions, visual acuity is reduced by about a factor of 10: 0.03 to 0.1 inch at 1 foot. I don't think this is the type of calculation where numbers to right of the decimal place have any meaning. In fact a range of values is probably more appropriate. For those who like formulas: D = diameter/acuity where D=distance (ft) at which object will be "invisible" diameter = diameter of guy line (inches) acuity = 0.003 to 0.01 for bright light 0.03 to 0.1 for dim light Remember, these values are for "average humans" before the aging process degraded their visual acuity. 73 de Bruce, WA7BNM (bhorn@hornucopia.com) Medical Physicist -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
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