Isolating the orange square from surrounding influences  will reveal that it is actually brown. The application to a real  environment is evident when processing visual information  that is influenced by surroundings. The ability to pick out an  airport in varied terrain or another aircraft in a light haze are  examples of problems with interpretation that make vigilance  all the more necessary. Figure 3-2  illustrates problems with perception. Both tables  are the same lengths. Objects are easily misinterpreted in  size to include both length and width. Being accustomed to  a 75-foot-wide runway on flat terrain is most likely going to  influence a pilot’s perception of a wider runway on uneven  terrain simply because of the inherent processing experience. Under conditions of dim illumination, aeronautical charts and  aircraft instruments can become unreadable unless adequate  flight deck lighting is available. In darkness, vision becomes  more sensitive to light. This process is called dark adaptation.  Although exposure to total darkness for at least 30 minutes is  required for complete dark adaptation, a pilot can achieve a  moderate degree of dark adaptation within 20 minutes under  dim red flight deck lighting. Red light distorts colors (filters the red spectrum), especially  on aeronautical charts, and makes it very difficult for the  eyes to focus on objects inside the aircraft. Pilots should  use it only where optimum outside night vision capability is  necessary. White flight deck lighting (dim lighting) should  be available when needed for map and instrument reading,  especially under IMC conditions. Since any degree of dark adaptation is lost within a few  seconds of viewing a bright light, pilots should close one eye  when using a light to preserve some degree of night vision.  During night flights in the vicinity of lightning, flight deck  lights should be turned up to help prevent loss of night vision  due to the bright flashes. Dark adaptation is also impaired by  exposure to cabin pressure altitudes above 5,000 feet, carbon  monoxide inhaled through smoking, deficiency of Vitamin  A in the diet, and prolonged exposure to bright sunlight. During flight in visual meteorological conditions (VMC),  the eyes are the major orientation source and usually  provide accurate and reliable information. Visual cues  usually prevail over false sensations from other sensory  systems. When these visual cues are taken away, as they  are in IMC, false sensations can cause the pilot to quickly  become disoriented. An effective way to counter these false sensations is to  recognize the problem, disregard the false sensations, rely  on the flight instruments, and use the eyes to determine the  aircraft attitude. The pilot must have an understanding of  the problem and the skill to control the aircraft using only  instrument indications. Vision Under Dim and Bright Illumination Figure 3-2.  Shepard’s tables illustrating problems with perception as both tables are the same length. 3-3